StarDate: Recent Episodes
Billy Henry
StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.
The number of confirmed planets in other star systems has reached about 6,000. But few of those planets are likely homes for life. Most are too hot, too cold, too “gassy,” or they’re zapped by too much radiation by their star.
A few planets are in the “well, maybe” category. They might be suitable for life, but the conditions aren’t perfect.
An example is a planet in the star system 82 Eridani. The system is about 20 light-years from Earth, and its star is similar to the Sun.
Astronomers have confirmed three planets in the system, with hints of more. Two of the planets are quite close to the star, so they’re too hot for life like that on Earth. But the third planet is more intriguing.
It’s about six times the mass of Earth, so it could be dense and rocky. Its average distance from the star is about a third farther than Earth’s distance from the Sun. At that range, the planet spends most of its time in the star’s habitable zone – the region where conditions are most comfortable for life.
But the planet’s orbit is so lopsided that the distance varies by more than a hundred million miles. So as the planet moves around 82 Eridani, surface temperatures range from hot enough to boil water to cold enough to freeze the entire surface. That makes it unlikely that anything lives on the planet. It is possible that life could exist below the surface – avoiding the extremes on this “yo-yoing” planet.
Script by Damond Benningfield
Astronomers have been searching for planets around one of our closest neighbor stars for decades. And they’ve reported the discovery of several. But the reports have come to naught – until now. Earlier this year, a team confirmed the presence of four planets – all of them smaller than Earth.
Barnard’s Star is six light-years away. Only the three stars of the Alpha Centauri system are closer. The star is much smaller and less massive than the Sun, and less than one percent as bright. In fact, it’s so faint that it wasn’t discovered until a little more than a century ago.
Barnard’s Star is ancient – probably twice the age of the Sun or older. So if it has planets, there’s been plenty of time for life to take hold. That’s made finding planets a high priority.
Last year, a team of astronomers confirmed one planet, and said there might be three more. All of those were confirmed in March. None of the planets is more than a third the mass of Earth. And they’re so close in that they orbit the star in a week or less. So even though Barnard’s Star is faint, the planets are all too hot to provide comfortable conditions for life.
Barnard’s Star is in Ophiuchus, the serpent-bearer. The constellation stretches across the east and southeast in early evening, and stands high in the south later on. But Barnard’s Star is too faint to see without a telescope.
We’ll have more about exoplanets tomorrow.
Script by Damond Benningfield
If you stare at one of the giant planets of the outer solar system long enough, with a big enough telescope, you’re likely to find some moons.
That was certainly the case a couple of years ago for Saturn. A research team scanned the space near Saturn with a large telescope in Hawaii. And earlier this year, the team reported its results: a haul of 128 previously unseen moons. That brought the planet’s total to 274. That’s three times the number of moons for second-place Jupiter – at least for now.
The newly found moons are small and faint – no more than a few miles in diameter. They follow odd orbits, including some that orbit backwards – in the opposite direction from Saturn’s rotation.
Some of the moons may be chunks of space rock that were captured by the giant planet’s gravity. Others may be the remains of larger moons that were blasted apart by collisions.
About a third of the moons may be the remnants of a single impact. They form a group named Mundilfari for a Norse god related to Saturn. It’s possible the impact took place within the past hundred million years – adding lots of little moons to Saturn’s family.
Look for Saturn near our own moon the next couple of mornings. The planet looks like a bright star. It’ll stand to the lower left of the Moon at dawn tomorrow, and closer to the right of the Moon on Thursday.
Tomorrow: a passel of planets for a nearby star.
Script by Damond Benningfield
If you sit on a big beachball, it gets mashed down. That makes it a little wider through the middle, and a little narrower from top to bottom. And that makes it look a lot like Alderamin, the brightest star of the constellation Cepheus the king. The star is about a third wider through the equator than through the poles. That’s not because some cosmic giant is sitting on it. Instead, it’s because the star spins like crazy.
Alderamin is about 50 light-years away, so it’s a fairly close neighbor. It’s nearing the end of the prime phase of life, even though it’s billions of years younger than the Sun. That’s because it’s twice as massive as the Sun. Heavier stars “burn” through their nuclear fuel much faster than lighter stars.
What really stands out about Alderamin, though, is its shape. The star’s equator rotates once every 12 hours, versus almost four weeks for the Sun. That forces gas outward around its middle, making the star look a bit more like a fat lozenge than a ball. As Alderamin continues to age, though, it will puff up to many times its current diameter. That will slow down its high-speed rotation, giving Alderamin a “rounder” appearance.
Cepheus is in the north and northeast at nightfall. Under fairly dark skies it’s easy to make out. It looks like a child’s drawing of a house. The peak of the roof is on the left during the evening, with Alderamin marking the top right corner of the sideways house.
Script by Damond Benningfield
Capricornus may be the most inventive constellation of the zodiac. For one thing, all of its stars are faint, so it takes some work to see any kind of pattern there. And for another, it represents the oddest creature in the heavens: a sea-goat – the front half of a goat plus the tail of a fish.
It’s easy to find the sea-goat’s location early tomorrow, because the Moon passes quite close to its brightest star. Unfortunately, the Moon will overpower most of the nearby stars, so you might want binoculars to help you see them.
The sea-goat’s leading light is known as Delta Capricorni or Deneb Algedi – the tail of the goat. It’s about 39 light-years away. It’s actually two stars locked in orbit around each other. The main star is twice the size and mass of the Sun, and about eight times the Sun’s brightness. The other star is smaller and fainter than the Sun.
Twice a day, Delta Cap fades a bit. That’s because its stars orbit each other once per day. And they’re aligned in such a way that they eclipse one other during each orbit. The system dims a bit more when the faint star passes in front of the bright one, and a bit less when it’s the other way around.
The stars of Capricornus form a wide triangle. Delta Cap is at the left point of the triangle. It climbs into good view by about 1 a.m. less than a degree from the bright Moon.
Script by Damond Benningfield
A perfect spiral galaxy would include a bright, round “bulge” of stars in the middle; glittering spiral arms wrapping around it; dark lanes of dust lacing through the arms; and bright star clusters sprinkled about like lights on a Christmas wreath.
In other words, it would look just like Messier 81, one of the best examples of a “grand design” spiral galaxy. It’s about 12 million light-years away, and appears close to the bowl of the Big Dipper. It’s a bit smaller and less massive than our own home galaxy, the Milky Way.
M81’s “bulge,” though, is much larger and brighter than the one in the center of the Milky Way. And the black hole in the galaxy’s heart is almost 20 times as massive as the Milky Way’s.
The spiral arms are outlined by the galaxy’s youngest, brightest stars. Over the past 600 million years or so, a major bout of starbirth has brightened the arms. That outburst is the result of gravitational interactions between M81 and two companion galaxies. The encounters compress big clouds of gas and dust. The clouds break into clumps, which then collapse to form stars – stars that make Messier 81 one of the most beautiful galaxies of all.
Under clear, dark skies, you can spot M81 with binoculars. Find the Big Dipper, which is high in the north at nightfall. M81 hangs below the bowl at that hour. It looks like an oval smudge of light that’s almost as wide as the Moon.
Script by Damond Benningfield
The stars look like they’re stuck in position – like fairy lights thumbtacked to a giant black canvas overhead. And over the course of a human lifetime – or many lifetimes – that’s true – there’s no way to see any motion without the help of sensitive instruments.
But that’s only because the stars are so far away. Every one of those little lights is moving – fast. They’re all orbiting the center of the Milky Way Galaxy, for example. And they’re moving either toward or away from Earth. So over millions of years, the configuration of the stars changes – constellations come and go. And the pattern of brightness changes as well – some stars fade, others grow brighter.
An example is Eltanin, the brightest star of Draco, the dragon. In fact, its name means “the great serpent.” It represents one of the dragon’s glowing eyes.
Today, Eltanin is a bit more than 150 light-years away. But it’s moving more or less toward us at more than 60,000 miles per hour. On the scale of the galaxy, that’s tiny – but it adds up. In about one and a half million years, it’ll be just 28 light-years away. If the star doesn’t change much over that period, it could be the brightest star in Earth’s night sky. And it could maintain that rating for hundreds of thousands of years.
Look for Eltanin high in the northeast at nightfall. It’s to the upper left of Vega, one of the brighter stars in the night sky – for now.
Script by Damond Benningfield
Two fairly bright lights are headed for an especially close meet-up: the planet Mars and the star Regulus, the heart of the lion. They’re a few degrees apart tonight, but they’ll draw even closer over the coming evenings.
Right now, Mars and Regulus are almost the same brightness. One way to tell them apart is their color – Mars looks pale orange, while Regulus is white with a hint of blue. Binoculars accentuate the colors.
Another way to tell them apart is to look for them to twinkle. Regulus does, but Mars doesn’t. That’s because Mars is a bigger target in our sky.
Regulus is thousands of times the size of Mars. But it’s so far away that we see it as nothing more than a pinpoint. That tiny beam of light is bent and twisted as it passes through the atmosphere. That causes the star to “twinkle.” It twinkles more when the air is more unsettled.
Mars, on the other hand, is close enough that it appears as a tiny disk, made up of many pinpoints. Each one twinkles, but they even out. So Mars appears to hold steady as it shines through even the most un-steady skies.
Look for Mars and Regulus about a third of the way up the western sky at nightfall. Regulus perches to the left or upper left of Mars. They’ll pass closest to one another on Monday and Tuesday. After that, they’ll move apart. At the same time, Mars will fade. A couple of weeks from now, Regulus will clearly outshine the Red Planet.
Script by Damond Benningfield
Anchorage, Alaska, isn’t quite the “land of the midnight Sun.” Tonight, there are about five hours between sunset and sunrise. But it is a land of midnight sunlight, because twilight never completely fades.
Twilight is the transition between day and night. Earth’s atmosphere scatters sunlight from the dayside to the fringes of the nightside.
But when, exactly, does twilight end? When is the sky really dark? As you might expect, astronomers have their own definition.
Astronomical twilight begins or ends when the Sun is 18 degrees below the horizon – about twice the width of your fist held at arm’s length. That’s when the sky’s as dark as it’s going to get.
Because of the Sun’s motion, astronomical twilight lasts a minimum of about an hour and 10 minutes. But because the Sun usually rises and sets at an angle, twilight can last a good deal longer.
During much of June and July, when the days are longest, twilight for much of the northern hemisphere lasts all night. The Sun never drops far below the horizon, so even though it’s out of sight, its light never disappears. So the people of Anchorage need some good blackout curtains to get a dark night’s sleep.
If you want a few hours of darkness, head south – someplace like Miami Beach. It gets a full seven hours between evening and morning twilight – hours that might be illuminated by the neon lights of South Beach, but not by the Sun.
Script by Damond Benningfield
Cold hands, warm heart. Still waters run deep. Feed a cold, starve a fever. The list of pithy old sayings goes on and on. But here’s a new one for you: long Sun, short Moon. It means that the full Moon does the opposite of what the Sun does. So when the Sun is in the sky for a long time, the full Moon makes itself scarce.
And that’s the case tonight. The full Moon of June has many names, including Flower, Strawberry, and Honey Moon. But it’s also known as the Short-Night Moon. That’s because it’s in view for less time than any other full Moon of the year.
From the northern hemisphere, the Sun passes highest across the sky at this time of year, and remains in view longest.
But because of the trail they follow, the Sun and the full Moon are like opposite ends of a seesaw. When one is up, the other is down. So right now, the full Moon passes low across the sky. And it rises around sunset and sets around sunrise.
The difference is greater as you go farther north. From Miami, the Sun will be above the horizon for almost 14 hours today, with the Moon popping into view for less than 10 and a half hours. From Duluth, Minnesota, it’s almost 16 hours versus less than eight hours. And from Anchorage, the Sun graces the sky for 19 hours, with the Moon showing up for a stingy hour and a half – an especially short appearance for the Short-Night Moon.
More about night and day tomorrow.
Script by Damond Benningfield
This might be Valentine’s Day, but some of the trappings of the day sound like they might be more suitable for Halloween. That’s because most of the gold in the universe – along with silver and platinum – may have been forged in collisions between dead stars.
Astronomers watched that process in action in 2017, when two neutron stars rammed together. That triggered a burst of gravitational waves – ripples in spacetime that were “heard” on Earth.
A neutron star is the tiny but ultra-dense corpse of a massive star. When two of them collide, they blast out huge amounts of matter. As the material cools, it builds up heavier elements – including gold.
Some of those elements are radioactive. As they decay, they glow, creating a kilonova – a fireball billions of times brighter than the Sun.
Telescopes saw the 2017 outburst less than two seconds after the gravitational waves arrived – the first time a source of the waves was seen in other forms. A recent study found that material from the blast was racing outward at almost half the speed of light.
Astronomers watched the formation of heavy elements almost minute by minute as the cloud of debris expanded. They couldn’t see the formation of gold itself, but they did see related elements. That allowed them to calculate the amount of gold that was created: enough to make 10 planets as heavy as Earth – perhaps providing the raw materials for future golden trinkets.
Script by Damond Benningfield
To nuke or not to nuke? That is the question: whether ’tis nobler to suffer the impacts of outrageous asteroids or to take arms against them, and by doing so end them. And a recent study says that, if necessary, nuke ’em.
When an asteroid a few miles wide hit Earth 66 million years ago, it wiped out the dinosaurs and most of the other life on our planet.
Such planet killers are rare, but they could still hit us. So scientists have studied ways to deflect them. With enough warning, we could pelt an asteroid with cannonballs – hunks of metal traveling at thousands of miles per hour. That could give the asteroid a big enough nudge to miss us.
If the asteroid is too big, or it’s discovered too late, the obvious solution seems to be nuclear weapons. But they have their own drawbacks – they might split an asteroid apart, pelting Earth with a bunch of big rocks instead of one giant one.
But a recent study by weapons experts found that an explosion in front of an asteroid might kick it away.
Researchers zapped some tiny simulated asteroids with X-rays in the Z Machine at Sandia National Laboratories – a device used to study nuclear weapons.The study found that X-rays from a one-megaton warhead, exploded above the surface, would vaporize some of the asteroid. The vaporized material would jet out into space like a rocket engine. That could push a two-and-a-half-mile asteroid off course – saving Earth from a cosmic catastrophe.
Script by Damond Benningfield
You don’t have to actually see something to know it’s there. You might feel it, hear it, or smell it. In other words, you use all your senses to suss it out.
Astronomers do that all the time. They may not see a star through their telescopes, for example, but they know it’s there because they use all their senses – special instruments that “see” what the eye cannot.
An example is Regulus, the brightest star of Leo. What we see as Regulus looks like a single point of light even through the largest telescopes. But instruments attached to those telescopes reveal a second star.
The instruments spread the light from the system into its individual wavelengths or colors – a spectrum. Each chemical element imprints a unique pattern in the spectrum. But Regulus shows two sets of those lines. And over time, the patterns move back and forth. That means Regulus has a companion just a few million miles away. The two objects orbit each other once every 40 days.
The companion is a white dwarf – the corpse of a once normal star. It’s much smaller and fainter than the system’s main star, and the two stars are quite close together. That makes it impossible to see the white dwarf through the glare. But we know it’s there – thanks to the extended senses of astronomy.
Regulus is quite close to the full Moon as night falls this evening. The Moon moves away from Regulus during the night, but they’re still close at dawn.
Script by Damond Benningfield
The weather can be a bit blustery at this time of year, with strong winds lofting dust into the sky. The dust can make the setting Sun look especially orange or red.
Astronomers see that same “redness” when they look at the stars beyond the Sun, and for the same reason: clouds of dust. In fact, the space between the stars is far from empty. It’s filled with gas and dust that form the “interstellar medium” – the ISM. This material accounts for about 15 percent of all the “normal” matter in our home galaxy, the Milky Way.
The interstellar medium is an extreme vacuum by any standard – it’s far emptier than any vacuum created in the laboratory. But there’s a lot of space between the stars, so the gas and dust add up.
Most of the ISM consists of hydrogen – atoms that were created in the Big Bang. But there’s also a smattering of other atoms and molecules, plus the tiny solid particles known as dust.
Many of the dust grains are about the size of the particles in cigarette smoke. That’s the right size to scatter blue wavelengths of light. The effect is similar to what makes the Sun look redder when it’s viewed through a thicker layer of air.
Interstellar dust makes far-away stars look redder than they really are, too. So to fully understand the stars, astronomers need to know how much dust they’re looking through – dust that reddens the view of the distant universe.
Script by Damond Benningfield
Outer space is one of those things you know when you see it. The sky is dark and quiet, with not enough air to sustain life. But just where space begins is hard to say – there’s no single definition that’s accepted by one and all.
In the last century, the National Advisory Committee for Aeronautics – the forerunner of NASA – said that space begins 50 miles up. At that altitude, the air pressure is only about a hundred-thousandth of the pressure at sea level. NASA and the Air Force have used that definition to award astronaut wings, beginning with the pilots of the X-15 rocketplane in the 1960s.
Later, engineer Theodore von Krmn devised a slightly higher boundary: 100 kilometers – about 62 miles. At that altitude, the air pressure is just one-millionth of the pressure at sea level. In such thin air, a craft must move at orbital velocity to stay aloft.
That altitude is known as the Krmn Line. Today, it’s the most commonly used definition for the edge of space. Anything that stays below that line is an aircraft, while anything that goes above it is a spacecraft. Hundreds of people have flown above that line – qualifying them as space travelers.
A smidgen of atmosphere extends above even the Karman Line – up to several thousand miles. It’s so thin, though, that it’s basically a vacuum – a region that certainly qualifies as “outer space.”
We’ll go deep into outer space tomorrow.
Script by Damond Benningfield
Things are changing on Mars. The Red Planet is about half way through spring in the northern hemisphere and autumn in the southern hemisphere. The switch triggers a kind of “see-saw” effect. As the north gets warmer, its polar ice cap gets smaller. And as the south gets colder, its ice cap gets bigger. That transition can cause the air pressure to vary by as much as a third across the entire planet.
The ice caps are made mainly of frozen water. They’re up to a couple of miles thick. They’re marked by spiral patterns of deep valleys – perhaps carved by strong winds.
A layer of dry ice forms atop each cap every autumn, and vanishes every spring. The carbon dioxide is pulled from the atmosphere, which is much thinner than Earth’s. So as the dry-ice cap moves from pole to pole, the atmospheric pressure changes by quite a bit.
There’s disagreement about what lies below the southern ice cap. A few studies have suggested there could be liquid water – perhaps in a thin layer, or mixed with the dust and rock in the ground. But other studies say that liquid water couldn’t survive in the conditions below the ice at the south pole of Mars.
Mars is in a crowded region of the sky tonight. It’s close to the upper right of the Moon at nightfall, and looks like a bright orange star. The true star Pollux is closer to the lower left of the Moon, with Castor, the other twin of Gemini, to their upper left.
Script by Damond Benningfield
The Big Bear is more than just the Big Dipper. The dipper outlines the body and tail of Ursa Major, the big bear. But the constellation covers much more territory. Some fainter stars outline the bear’s legs and head. But it’s the stars of the dipper that we most notice – not only because they’re fairly bright, but because they form an easy-to-see pattern.
The dipper is an “asterism” – a group of stars that forms a discernible pattern, but that doesn’t form a whole constellation. An asterism can be part of a constellation, as the dipper is, or it can incorporate stars from two or more constellations.
A couple of examples are in good view this evening. A small one is the Circlet of Pisces – five stars that outline the head of one of the fish of Pisces. The stars aren’t that bright, but they form a compact pattern, making the circlet easier to pick out. And it has a bright pointer: It’s close to the lower right of Venus, the “evening star.”
On the other end of the spectrum is the Winter Hexagon or Winter Circle. It is outlined by seven stars – most of them among the brightest in the night sky. The pattern spans more than six times the width of your fist held at arm’s length. It ranges from Sirius, the brightest star in the night sky, which is low in the southeast at nightfall, to yellow-orange Capella high in the east. It incorporates stars from six constellations – the largest of all the well-known asterisms.
Script by Damond Benningfield
The gibbous Moon passes across a special spot tonight. It lines up opposite the center of the Milky Way Galaxy – the galactic anti-center. In that direction, we’re looking toward the rim of the galaxy’s disk. The rim is about 25,000 light-years away, with intergalactic space beyond.
The center of the galaxy is in Sagittarius. When we look in that direction we stare into thick clouds of stars, along with dark clouds of dust – places where more stars are being born.
But when we look in the opposite direction the view is much less impressive. There aren’t as many stars or dust clouds. And the stars thin out as you get closer to the rim.
Beyond that, we’re looking into the galaxy’s “halo” – a region that extends hundreds of thousands of light-years into space. It contains a few giant star clusters, and a smattering of individual stars. Almost all of them are ancient – dating to the earliest days of the Milky Way itself.
And beyond the halo, there’s not much at all – some wisps of gas, and an occasional star or free-ranging planet. It’s millions of light-years to the next galaxy – through the vastness of intergalactic space.
The closest star to the anticenter is Elnath, the second-brightest star of Taurus. It marks the tip of one of the bull’s horns. It’s just above the Moon at nightfall. The brilliant planet Jupiter and the star Aldebaran – the bull’s eye – stand farther to the right or upper right of the Moon.
Script by Damond Benningfield
The Moon probably was born when the young Earth was hit by another planet. That blasted a lot of debris into space. Much of it came together to form the Moon.
But Earth wasn’t the only world to get smacked around in the early solar system. One of the others might have been Ganymede, the largest moon of Jupiter. A recent study suggested that a giant asteroid slammed into it, making it wobble for a thousand years.
Ganymede is the largest moon in the solar system – bigger than the planet Mercury. It probably has an ocean of liquid water below its icy crust. The ocean might be 60 miles deep, and hold more water than all of Earth’s oceans combined.
The new study looked at some long ripples on the surface, the way Ganymede spins, and other evidence. Researchers then used computer models to simulate Ganymede’s history. Their work suggested that Ganymede was hit by an asteroid about four billion years ago. The asteroid was almost 200 miles in diameter, and hit near the north pole. That caused Ganymede to wobble. Eventually, it flipped over on its side. What had been the equator became the poles as Ganymede settled down after a massive impact.
Jupiter is close to our moon at nightfall. It looks like a brilliant star. Aldebaran, the brightest star of Taurus, is to the lower right of Jupiter. Binoculars reveal Jupiter’s four big moons, including Ganymede – a world that might have suffered a “big whack” billions of years ago.
Script by Damond Benningfield
An odd “zombie” star has grabbed its companion in a magnetic embrace. It keeps the two stars synchronized, and it pulls gas from the companion.
The system is A-M Herculis. It’s almost 300 light-years away, in the constellation Hercules.
The main star in the system is a white dwarf — the corpse of a once-normal star. It’s about two-thirds as massive as the Sun, but only about as big as Earth. That means it’s extremely dense, so its gravity is strong.
The star’s magnetic field is millions of times stronger than the Sun’s. And that’s bad for the companion – a cool, faint ember known as a red dwarf. The stars are so close that they orbit each other every three hours. At that range, the magnetic field of the white dwarf exerts a powerful pull. It’s made the two stars rotate in such a way that the same hemisphere of each star always faces the other – just as the same hemisphere of the Moon always faces Earth.
The field also pulls gas from the companion. In most systems like this, the infalling gas forms a wide, spinning disk. But in the case of A-M Herculis, it plunges directly onto the white dwarf, guided by the magnetic field. The streamer varies – thicker at some times, thinner at others. But it piles onto the poles of the white dwarf, making the star hotter and brighter – renewed vigor for a stellar zombie.
Hercules is high in the sky at dawn. But A-M Herc is much too faint to see without a telescope.
Script by Damond Benningfield
The bright Moon has some bright companions tonight: the planet Jupiter and the stars Aldebaran and Elnath. But the Moon washes out some fainter lights: the Leonid meteor shower.
The shower is expected to reach its peak late tonight – perhaps 15 or 20 meteors per hour. But only the brightest of them will shine through the glare of the just-past-full Moon.
The nearby planet and stars will be much easier to see – especially Jupiter, which will stand below the Moon as they climb into good view. It’s the brightest pinpoint of light in the sky for most of the night.
Jupiter is so bright for several reasons. For one, it’s the largest planet in the solar system – 11 times the diameter of Earth. For another, it’s blanketed by clouds that reflect most of the sunlight that strikes them. And finally, the planet is especially close now – less than 400 million miles away. It’ll be at its closest early next month.
Aldebaran is to the lower right of the Moon. It’s Taurus’s brightest star. It represents the bull’s eye. It shines bright orange, but the color might be muted by the nearby Moon.
Elnath is the second-brightest star of Taurus. It’s at the tip of one of the bull’s horns. It, too, is washed out by the moonlight. Even so, it should still be pretty easy to pick out – part of a beautiful arc around the gibbous Moon.
Jupiter and Elnath will be even closer to the Moon tomorrow night. More about that tomorrow.
Script by Damond Benningfield
The first intentional message to other civilizations was beamed into the galaxy 50 years ago tomorrow. There wasn’t much to it – just 1,679 bits of data. When properly decoded, the message yields a picture – stick-figure outlines of a person and the message’s planet of origin, for example. The image also features the facility that beamed it into space: the giant Arecibo radio telescope, which collapsed a few years ago.
The Arecibo message was conceived by Frank Drake. He was a pioneer in SETI – the search for extraterrestrial intelligence. He’d conducted the first search for radio signals just 15 years earlier. One of his collaborators was celebrity astronomer Carl Sagan.
The message was intended primarily as a publicity stunt. Arecibo had just received a major upgrade, and astronomers wanted to show it off. So the message was transmitted just once – it wasn’t repeated.
Other messages have followed, from radio telescopes around the world. Today, though, scientists and others are debating the wisdom of alerting the rest of the galaxy to our presence. They wonder whether messages to the stars might bring an unpleasant response.
The target for the Arecibo message was M13, a giant star cluster in Hercules. It’s in the west-northwest at nightfall, and it’s an easy target for binoculars or a small telescope. But it’s so far away that the message won’t get there for another 25,000 years.
Script by Damond Benningfield
Half of the planets discovered in other star systems are about the same size and mass as Uranus and Neptune, two of the giants of our own solar system. But we don’t know much about these exoplanets – in part because we don’t know much about Uranus and Neptune themselves. They’re billions of miles away, and only one mission has visited either planet.
But scientists hope to learn more around the middle of the century. A panel of scientists recommended a “flagship” mission to Uranus as NASA’s next big project for planetary exploration. An orbiter would loop around Uranus and its moons for years, while a probe would parachute into the planet’s atmosphere.
Uranus is an oddball. It lies on its side – probably the result of a collision with another planet when it was young. Scientists would like to know more about the impact and how it affected the planet’s interior. The sideways orientation also gives Uranus a cycle of seasons unlike that of any other planet. And some of the planet’s moons could have oceans of liquid water below their icy crusts.
NASA hasn’t yet started on the mission – in part because it’s working on a lot of other big-ticket items. So it’ll be a while before we get a close look at this common type of giant planet.
Right now, Uranus is low in the east as darkness falls. Tonight, it’s not too far to the lower left of the Moon. But it’s so faint that you need binoculars or a telescope to see it.
Script by Damond Benningfield
It’s cold in the outer solar system. The planet Uranus, for example, is 20 times farther from the Sun than Earth is. As a result, its 28 known moons all shiver at hundreds of degrees below zero. Yet several of the planet’s bigger moons might have active volcanoes. Instead of molten rock, they’d belch out molten ice – a slushy brew from buried oceans of liquid water.
We don’t know for sure if any of the moons have ice volcanoes, but there’s evidence that they do. The surfaces of the moons are fairly young, for example. That suggests that something is renewing them – like material from the interior. And a couple of the moons appear to be pumping material into the space around Uranus.
Recent observations by Webb Space Telescope found additional evidence for an ocean on the moon Ariel. It’s coated with frozen carbon dioxide. Webb found the layer of C-O-2 is especially thick. And it’s mixed with carbon monoxide. Both compounds should quickly vaporize and drift off into space. Their presence suggests the supply is being renewed – perhaps by volcanoes belching ice from a hidden ocean.
Uranus is putting in its best appearance of the year. The giant planet rises around sunset and is in view all night. It’s brightest for the year, too, although you still need binoculars to pick it out. Tonight, it lines up about half way between the almost-full Moon and the bright planet Jupiter.
We’ll have more about Uranus tomorrow.
Script by Damond Benningfield
Polar vortex has entered the American lexicon with a fury in recent years. It’s used to describe especially bitter outbreaks of winter weather. The northern hemisphere actually has two polar vortexes. The one that gives us the extreme cold is fairly low in the atmosphere. It’s formed by jet streams that encircle the pole that sometimes plunge southward. The other is much higher in the atmosphere.
The higher vortexes are seen on every planet and moon in the solar system with much of an atmosphere. That includes Uranus, the third-largest planet. Scientists found evidence to confirm the vortex last year.
Hints of a vortex around the north pole were seen in 2015. More recently, scientists looked at the pole with a giant radio telescope in New Mexico. They saw an especially bright area at the pole itself, with a dark ring around it. The bright region was warmer than the surrounding atmosphere. The combination provides strong evidence of a polar vortex.
Air in the upper atmosphere moves toward the poles. It’s deflected by the planet’s high-speed rotation – forming a “vortex” around the north pole.
Uranus is putting in its best appearance of the year. It’s lining up opposite the Sun, so it rises around sunset and is in view all night. It’s brightest for the year as well. But you still need binoculars or a telescope to see it, along the border between Taurus and Aries.
We’ll have more about Uranus tomorrow.
Script by Damond Benningfield
It’s springtime – on Mars, anyway – because today is the spring equinox for the Red Planet’s northern hemisphere.
Like the seasons on Earth, the seasons on Mars are the result of the planet’s tilt on its axis. In fact, the two planets are tilted at almost the same angle. So the north pole dips toward the Sun at the start of northern summer, while the south pole dips sunward at the start of northern winter. The equinoxes are half way between those points.
But there are some differences between the seasons on Earth and Mars. Mars’s orbit is more stretched out than Earth’s orbit, so there’s a bigger difference in the planet’s distance from the Sun. Mars’s distance varies by about 26 million miles.
That has a couple of effects. For one thing, it creates a big disparity between the seasons in the northern and southern hemispheres. Mars is farthest from the Sun during southern winter, and closest during summer. That means southern winters are colder than northern winters, while summers are warmer.
And second, Mars moves fastest when it’s close to the Sun, and slowest when it’s far away. That causes a big difference in the length of the seasons. Northern spring is the longest – it lasts 194 Mars days. Northern fall is the shortest – just 142 days.
Look for bright orange Mars climbing into good view in late evening, and high in the southwest at first light – a world that’s springing into a new season.
Script by Damond Benningfield
The Moon will stage a pair of cover-ups over the next couple of nights. The first happens tonight, when the Moon covers up the planet Saturn. And the second happens just 24 hours later, when it covers the planet Neptune.
The cover-ups are known as occultations. They occur because the Moon and planets all stay close to the ecliptic – the Sun’s path across the sky. But they all stray a few degrees to either side of the ecliptic. So most months, the alignment is off by a bit, so the Moon just misses the planets.
At times, though, the geometry is just right, as it is now – at least for parts of the world. Tonight, for example, the occultation of Saturn will be visible from a bit of South America, most of Central America, and the southern half of Florida. There, Saturn will disappear at about 9:20 p.m. It’ll remain out of sight for about 45 minutes. Because Saturn forms a tiny disk in our sky, it’ll take a few seconds for the planet to disappear and reappear – it won’t instantly blink off and back on.
The rest of the United States will see an especially close encounter between Saturn and the Moon. Saturn looks like a bright star, and will pass just a fraction of a degree from the Moon.
Tomorrow night, it’s Neptune’s turn. The path of the occultation will cross most of the United States. But Neptune is so faint that you need a telescope to watch the giant planet vanish – another cover-up for the gibbous Moon.
Script by Damond Benningfield
The bright Moon washes out the fainter stars tonight. One that shines through is Hamal, the leading light of Aries, the ram. It’s in the east at nightfall. It’s about 65 light-years away. And it’s a giant – bigger, heavier, and brighter than the Sun.
The other stars of Aries are tougher to see. And some stars that once formed separate constellations around it are impossible to see. In fact, they were tough to spot even when they were first outlined.
To the left of Hamal is Triangulum Minus, the little triangle. It was created by German astronomer Johannes Hevelius, in 1687. Its three stars are all quite faint. So even without the moonlight, they’re visible only under dark skies, away from city lights.
Below Hamal is Musca Borealis, the northern fly. It consists of four faint stars. The constellation was created by Petrus Plancius, in 1612. His original name for it was Apes, the bees. Later, another astronomer called it Vespa, the wasp. Hevelius then took over. He kept the buzzy theme, but he went with Musca, the fly. But there was already a fly in the southern hemisphere, so astronomers clarified matters by adding “northern” to the name.
In 1930, the International Astronomical Union adopted 88 official constellations, all with well-defined borders. The little triangle was incorporated into Triangulum. And the stars of the northern fly became part of Aries – buzzing around the rump of the ram.
Script by Damond Benningfield
Capella is a big mismatch. It’s a system of four stars, divided into two widely separated pairs. The members of one pair are both about two and a half times the mass of the Sun. But the members of the other pair are only about half the Sun’s mass. As a result, the two pairs face quite different futures.
Capella is the brightest star of Auriga, the charioteer, and the sixth-brightest star in the entire night sky. It climbs into good view in the northeast in early evening and soars high overhead during the night.
The system appears to be about 600 million years old – four billion years younger than the Sun. Yet the stars in the heavier pair are both at the end of life. They’ve burned through the original hydrogen fuel in their cores. That’s made them puff up to giant proportions.
Before long, both stars will shed their outer layers. The stars are close enough together that the expelled gas should act like a brake, causing the stars to spiral close together. But as the gas disperses, the stars will be much lighter. That will loosen their grip on each other, causing them to move farther apart. So no one is quite sure what the system’s final configuration will look like.
The smaller stars, on the other hand, will remain in the prime phase of life for tens of billions of years longer. But as the heavier stars trim down, the two pairs are likely to drift apart – splitting up a stellar quartet.
Script by Damond Benningfield
Scientists don’t have a crystal ball to help them foretell the future of the universe. But they can devise ideas about the future based on their understanding of the history of the universe and the laws of nature.
Based on that, perhaps the leading idea about the fate of the universe is the Big Freeze: The universe will get colder and darker, and eventually disintegrate into a soup of particles.
The key ingredient of the Big Freeze is dark energy. Scientists don’t yet understand its nature. But it causes the universe to expand faster as it ages. And if it keeps its foot on the accelerator, the universe faces a bleak future.
Hundreds of billions of years from now, the expansion rate will outpace the speed of light. Galaxies will disappear from each other – their light won’t move fast enough to reach most of the other galaxies.
The final stars will be born in a few trillion years. By then, most stars will have expired. Galaxies will consist mainly of the corpses of stars, plus some faint stars and smaller objects.
Over the eons, all the stars will die, and the stellar corpses will evaporate. And after trillions upon trillions of years, even black holes will vanish. Only ghostly particles will remain.
This future is far from certain. Scientists have many questions about dark energy and more. They’ll need to peer deeper into their crystal balls – the laws of nature – to tell us whether the universe will die in a Big Freeze.
Script by Damond Benningfield
A faint glow fills the entire universe – the “afterglow” of the Big Bang. The glow was created when the first atoms formed – 380,000 years after the Big Bang. But the glow isn’t smooth – it has tiny ripples and bumps. That’s because the universe itself wasn’t smooth – there were slight differences in the density of matter. Without those differences, we wouldn’t exist.
The denser regions had a slightly stronger gravitational pull, so they drew in the material to make the first stars and galaxies.
The first stars were born in as little as a hundred million years. They were made almost entirely of hydrogen and helium, which were created in the Big Bang.
The stars probably were quite heavy, so they burned out in a hurry. They forged heavier elements in their cores, then blasted them into space when they died. Some of those elements were incorporated into later generations of stars. Those stars created more heavy elements and flung them into space as well, and so on. The heavier elements are the ingredients for planets and everything on them – including us.
Galaxies began to form about four hundred million years after the Big Bang, as stars and gas clouds clumped together. More stars and galaxies are being born today, but not as many. In fact, most of the stars and galaxies that will ever be born have already taken shape. So the universe may face a cold, dark fate, and we’ll talk about that tomorrow.
Script by Damond Benningfield
Our universe has a long and complicated history. And scientists are still trying to understand it all.
The general picture says the universe was born 13.8 billion years ago, in the Big Bang. For the first tiny fraction of a second, the universe expanded at many times the speed of light – an epoch known as cosmic inflation. When inflation ended, the expansion slowed dramatically. But a lot happened over the following few minutes.
During the first second, the basic forces of nature took shape: gravity, electromagnetism, and the forces that bind matter together. These forces made it possible to forge protons and neutrons.
By about three minutes, the universe had expanded and cooled enough for these particles to stick together. They formed the nuclei of the first elements – mainly hydrogen and helium.
The universe was still extremely hot and dense. And it was “foggy,” so we can’t see anything from that era. By about 380,000 years, though, the fog began to clear. Electrons latched on to the nuclei to form complete atoms. That process left a faint “afterglow” that we see across the entire universe.
There are lots of questions about the details of this picture. And some scientists aren’t convinced about the overall outline – they have different views about the age of the universe, whether inflation ever happened, and more.
There’s a little more agreement about what came next, and we’ll talk about that tomorrow.
Script by Damond Benningfield
It’s hard to imagine a less comfortable place for life than the clouds of Venus. They’re made mainly of sulfuric acid – something you wouldn’t want to dip your fingers into. Yet studies in the past few years are raising at least the possibility that microscopic life could inhabit those clouds.
There’s almost no way for anything to live on the surface of the planet. The atmosphere is too hot, dense, and toxic. But the clouds are about 30 miles high, where the conditions are more like those on Earth.
A few years ago, scientists reported finding phosphine in the clouds. On Earth, it’s a compound that’s almost always produced by living organisms. Other studies have found no trace of it. But earlier this year, astronomers reported finding new evidence of the compound.
Another study this year reported finding ammonia. On Earth, it’s produced mainly by living organisms and industrial processes. And yet another study said that some of the key building blocks in amino acids could survive in a high concentration of sulfuric acid.
None of that means that anything actually lives in the clouds. But it does mean that scientists will be taking a much closer look at Venus’s clouds in the years ahead.
Venus is the brilliant “evening star.” It’s quite low in the southwest as night falls. Tonight, it’s close to the upper right of the crescent Moon. It’ll be a little farther to the lower right of the Moon tomorrow night.
Script by Damond Benningfield
Star clusters line up in the evening sky at this time of year like pearls on a necklace. As the sky gets nice and dark, they climb straight up the northeastern sky. They stretch from the bright star Capella, which is quite low; up through the “W” of Cassiopeia; then to Cygnus, the tail of the swan, high overhead.
There’s a good line of clusters because that path outlines the Milky Way – the subtle glow of the disk of our home galaxy. Most of the clusters are classified as “open.” All of the stars in such a cluster were born together, from a giant cloud of gas and dust. But as the clusters orbit the center of the Milky Way, they’re slowly pulled apart. So over time, all the stars in such a cluster go their own way.
Perhaps the highlight of this path is the Double Cluster – two clusters in Perseus, just below Cassiopeia. Under dark skies, they’re visible to the unaided eye as a faint cloud of light.
Individually, the clusters are known as NGC 869 and 884. They’re about 7500 light-years away. Combined, their stars and gas add up to about 20 thousand times the mass of the Sun. And they’re quite young as stars go – about 14 million years. At that tender age, the clusters haven’t had time to fall apart. And with their great mass, they’re likely to hold together longer than most clusters – perhaps several hundred million years.
Tomorrow: the crescent Moon and the “evening star.”
Script by Damond Benningfield
Our home galaxy, the Milky Way, doesn’t have enough satellites – smaller galaxies in orbit around it. Unless it has too many. That’s the conundrum facing the scientists who study how galaxies are born.
So far, astronomers have discovered about 60 galaxies orbiting the Milky Way. Most of them are much smaller than the Milky Way. That makes them faint and hard to find. But models of galaxy formation say the Milky Way should have more than 200 satellites. The difference has been called the “missing satellite problem.”
The models are based on ideas about dark matter. It appears to make up about 85 percent of all the matter in the universe. But it doesn’t produce any energy that we can see. It reveals its presence only through its gravitational pull on the visible matter around it.
In the early universe, dark matter should have congregated in big clumps. They pulled in normal matter, which formed stars and galaxies. Smaller clumps should have given birth to smaller galaxies around the big ones. But the number of smaller galaxies hasn’t matched those predictions.
A recent search of a small patch of sky discovered several new small galaxies. Based on that, researchers suggested the Milky Way could have about 500 satellites.
Many of these little guys could have been absorbed by the Milky Way over the eons. Or perhaps hundreds of them still await discovery – tiny galaxies orbiting the giant Milky Way.
Script by Damond Benningfield
Scientists have been playing a game of hide-and-seek for decades. They’re looking for most of the mass of the universe, which is hidden from view. So far, they haven’t found it. So they keep widening the search – coming up with new explanations for what the missing mass might be, and how they might find it.
Their quarry is dark matter, which appears to account for about 85 percent of all the matter in the universe. It doesn’t produce any energy of its own, and it almost never interacts with “normal” matter. But astronomers “see” its presence through its gravitational pull on the visible matter around it.
For a long time, the best explanation seemed to be some type of especially heavy particle. But experiments that look for it have come up empty.
So scientists have devised other possible explanations. One is an especially lightweight particle – as little as a billion billionth of the mass of the lightest bit of normal matter. Another is primordial black holes – tiny but heavy objects created in the Big Bang. And one of the wildest explanations is “tachyons” – hypothetical particles that would move faster than light.
Some scientists argue that dark matter doesn’t exist at all. One team, for example, suggests the universe is much older than the currently accepted 13.8 billion years. If so, then dark matter wouldn’t be needed – and neither would the game of hide-and-seek.
More about dark matter tomorrow.
Script by Damond Benningfield
Sometimes, nature is kind and generous. In April, for example, it produced a total solar eclipse that was seen by tens of millions.
At other times, though, nature is more impish. An example of that comes up tomorrow. There’s another solar eclipse. But this time, the Moon will be farthest from Earth for the entire year. So the Sun will encircle the Moon with a wide ring of fire – an annular eclipse. And not many people will see it – almost its entire path is over the Pacific Ocean.
During an annular eclipse, the Moon lines up directly in front of the Sun, as it does during a total eclipse. But the Moon is farther from Earth than average, so it can’t completely cover the Sun. Tomorrow’s eclipse peaks less than an hour before the Moon reaches its greatest distance from Earth for the entire year – more than 252,500 miles – almost 14,000 miles farther than the average distance. So the Moon will block no more than 87 percent of the Sun’s disk.
Even so, it should be a great sight for anyone along the path – as long as they have the proper eye protection.
The eclipse begins south of Hawaii, then sweeps toward the southeast. It nicks the tip of South America, then ends over the South Atlantic. Hawaii will see a partial eclipse, beginning at sunrise. And North America? Well, nature’s not as generous this time. None of the eclipse will be visible from anywhere on the continent.
Script by Damond Benningfield
This is the time of year when we start thinking about cold snaps – frontal systems that cause sudden drops in temperature, and often bring clouds.
A recent study suggests that our entire planet went through a major cold snap a few million years ago. It was caused by a giant cloud – a dense clump of material between the stars.
The space between stars contains many clouds of gas and dust. In fact, we’re inside one right now – the Local Interstellar Cloud. But it’s quite thin, so it doesn’t have much impact on the solar system.
The study says we might have passed through a much thicker cloud two million to three million years ago. Its material could have been 15 thousand times denser than the current cloud.
That could have drastically squeezed the magnetic “bubble” generated by the Sun. Today, the bubble extends more than a hundred times the distance from Earth to the Sun. But in the denser cloud, it could have been squeezed to just a quarter of the Earth-Sun distance.
Since Earth would have been outside the Sun’s protective bubble, it would have been bombarded by more cosmic rays. And dust from the interstellar cloud might have settled into our atmosphere.
The researchers say that could have had an impact on Earth’s climate – perhaps making it much cooler. That could have killed off some life, and perhaps altered the development of human ancestors – possible impacts of an interstellar cold snap.
Script by Damond Benningfield
Royalty creeps across the southern sky on autumn nights: Fomalhaut, the brightest star of Piscis Austrinus, the southern fish. To the people of ancient Persia, it was one of four “royal” stars, along with Aldebaran, Regulus, and Antares. Each star ruled the sky during a different season. For Fomalhaut, it was the autumn sky.
Fomalhaut probably was a pretty easy choice. It’s the only bright star in a large region of the sky. And at this time of year, it’s in view pretty much all night.
Fomalhaut also was considered the protector of the winter solstice. About 5,000 years ago, the star aligned in the same direction as the Sun at noon on the solstice.
The Fomalhaut system appears to consist of at least three stars. The brightest is Fomalhaut A – the one that’s visible to the unaided eye. The star is about twice as big and heavy as the Sun, and quite a bit brighter. It’s about 25 light-years away.
A giant disk of dust encircles the star. For a few years, it looked like there might be a planet inside the disk. Astronomers even gave it a name: Dagon. But it turned out to be just a big clump of dust – the likely debris from a collision between two big asteroids.
Fomalhaut stands quite low in the southeast as the sky gets good and dark, and due south around midnight. Don’t confuse it with brighter Saturn, well to its upper left. Fomalhaut is in view all night – a royal star for autumn nights.
Script by Damond Benningfield
The Moon is a thin crescent in the dawn sky tomorrow. The Sun lights up only about one-tenth of the lunar hemisphere that faces our way. That’s the part of the Moon where it’s daylight. It’s nighttime across the rest of the disk.
But that doesn’t mean you can’t see that part of the Moon. It forms a ghostly presence, illuminated by earthshine – sunlight reflecting off of Earth. And the earthshine is pretty bright now, because Earth would appear 90 percent “full.” Because our planet is much bigger and more reflective than the Moon, it shines many times brighter than a full Moon appears from Earth. Tomorrow, the earthshine will be so intense that you can easily make out lunar features through a pair of binoculars.
And because the same side of the Moon always faces Earth, our planet sticks around in the same spot in the lunar sky, day and night. So future Earthwatchers will see it go through an entire cycle of phases every 29 and a half days, just as the Moon does. But from any given spot on the Moon, Earth won’t move – it’ll be “locked” at the same point in the sky.
Look for the crescent Moon in the east beginning an hour or two before dawn. It has a bright companion: Regulus, the star that marks the heart of the lion. It stands close to the right or upper right of the Moon. The Moon will be an even thinner crescent on Monday, but still easy to make out – thanks to the light of the silvery Earth.
Script by Damond Benningfield
If you’re a super-advanced civilization and you’re running out of energy, there’s a simple solution: Dismantle part of your planetary system to build “megastructures” around your star. Known as Dyson Spheres, they’d gather most of the star’s energy, giving you an almost limitless supply.
A recent study has found possible evidence of them. Most or all of the candidate objects are likely to have a natural origin: distant galaxies, or clouds of debris around a star. But astronomers are following up just in case.
The “spheres” wouldn’t completely surround a star. Instead, they’d consist of many huge panels in separate orbits around the star. They’d emit heat, so they’d glow in the infrared. So astronomers have been looking for the right kind of infrared glow for years.
In the recent study, a team scoured observations of about five million stars within a thousand light-years of Earth. They used many filters to narrow the list. And they came up with seven candidates. All of them are red dwarfs – stars that are much smaller, cooler, and fainter than the Sun. Such stars live a long time – long enough for a civilization to develop and grow – and surround the star with a Dyson Sphere.
Two of the candidate stars are near the “head” of one of the fish of Pisces. The figure is low in the east at nightfall, to the left of the bright planet Saturn. The candidates are much too faint to see without a telescope.
Script by Damond Benningfield
The Milky Way Galaxy is like a big blender filled with many ingredients. But it hasn’t been blended enough for all the ingredients to completely stir in. So it’s possible to make some of them out – to see some of the raw ingredients that created the galaxy.
Astronomers recently reported the discovery of what could be two of the earliest ingredients – ribbons of stars that could be the remnants of two small galaxies. If so, they were stirred into the Milky Way about 12 billion years ago, when the galaxy was just taking shape.
The possible remnants were named Shiva and Shakti, after a Hindu god and goddess. They were discovered by Gaia, a space telescope that’s measuring the composition and motion of more than a billion stars.
Each remnant consists of a ribbon of stars that spans thousands of light-years. The stars in each ribbon appear to move through the galaxy together. And they all have a similar make-up. That suggests they were born together – as members of small galaxies.
The larger Milky Way pulled those galaxies in, then ripped them apart. Today, most of their stars have been stirred in with the rest of the Milky Way. But a few may hold on to some of their original identity – some of the earliest building blocks of the Milky Way.
If you have dark skies, look for the glowing band of the Milky Way arching high overhead as night falls – a giant blender that’s not completely stirred up.
Script by Damond Benningfield
You can tell whether a train or a police car is moving toward or away from you just by listening. Its horn or siren changes pitch – higher if it’s moving toward you, lower if it’s moving away.
The same principle applies to the stars. Their light is shifted to longer or shorter wavelengths. Measuring that shift reveals the star’s motion – its “radial velocity.”
An example is Pollux, the brightest star of Gemini. It’s close to the Moon at first light tomorrow. Its radial velocity tells us that the star is moving toward us at more than 7,000 miles per hour. That sounds fast. But at the star’s distance of almost 34 light-years, it would take millions of years to reach us. Pollux’s orbit is also carrying it sideways, so the star will never even get close.
By measuring its radial velocity, astronomers at McDonald Observatory discovered a planet orbiting Pollux. As it orbits, the planet tugs at the star, changing its motion toward us by a few miles per hour.
Precise measurements of that change revealed some details. The planet is a bit more than twice as massive as Jupiter, the giant of our own solar system. It’s a little farther from Pollux than Mars is from the Sun. And it orbits the star once every 19 months.
Astronomers named the planet Thestias – a version of Leda, the mother of Pollux – a planet discovered by measuring a tiny shift in the star’s light.
Script by Damond Benningfield
When Mars was young, the planet was much warmer and wetter than it is today, with a fairly thick atmosphere. Most of that atmosphere leaked away into space. And scientists are still trying to understand how that happened.
They should learn more from twin spacecraft that are scheduled to launch soon. The mission is called Escapade, while the individual craft are designated Blue and Gold. If they launch on time, they’ll enter orbit around Mars a year from now.
The probes will study the weak Martian magnetic field and how it interacts with the solar wind – a “breeze” of charged particles from the Sun.
Because Martian gravity is much weaker than Earth’s gravity, molecules in its early atmosphere drifted to the top of the atmosphere. There, radiation from the Sun split the molecules apart. The solar wind then carried off some of the residue. Over the eons, that depleted the atmosphere. Today, it’s less than one percent as thick as Earth’s.
Many of the details of that process are unclear. The Escapade probes will monitor that process from different perspectives, offering a 3-D view of what’s going on. That should help scientists fill in the blanks – providing a much better understanding of how Mars lost its air.
Mars perches close to the Moon early tomorrow. They climb into view by 1 or 1:30 a.m., and stand high in the sky at first light. Mars looks like a bright orange star to the lower right of the Moon.
Script by Damond Benningfield
NOTE: Since this program was recorded NASA has delayed the launch of Escapade until at least 2025.
Jupiter might have “blinked” for more than a century. A storm in its southern hemisphere might have winked out, with another eventually taking its place – today’s Great Red Spot.
Scientists first reported a spot in Jupiter’s southern hemisphere as early as 1632, and definitely by 1665. But there were no records of it from the early 1700s to the early 1800s. So there’s been a debate about whether the spot disappeared, or astronomers simply missed it.
A recent study argues that the original spot vanished. Researchers combed through all the records of Jupiter they could find – including those by some of the most accomplished observers of the time. And there were no reports of a big, dark spot. That suggests the original storm fizzled out, and a new one fired up in the same location.
The current version was first reported in 1831. Since then, it’s changed dramatically. At first, it was an oval about three times as wide as Earth. Today, it’s rounder, and about the same size as Earth.
The new study says the Great Red Spot probably sprang from the interplay of two powerful jet streams. Today, winds at its perimeter reach almost 300 miles per hour. And they’re getting faster as the spot shrinks – perhaps to once again blink out.
Jupiter stands to the right of the Moon as they climb into good view, around midnight. It looks like a brilliant star. A small telescope will reveal the Great Red Spot.
Script by Damond Benningfield
Three bright companions cradle the Moon early tomorrow: the planet Jupiter and the brightest stars of Taurus. The whole group climbs into good view by midnight, and stands high in the sky at dawn. The star Elnath is to the left of the Moon at that hour, with brilliant Jupiter to the lower left of the Moon, and Aldebaran a little farther below the Moon.
There’s a big gap in the distances to the four bodies. Yet they’re all among our closest neighbors.
On average, the Moon is the closest of all. Tonight, it’s just 230,000 miles away. Small asteroids occasionally pass closer than that. But most of the time, those bodies are much farther.
Jupiter is the next-closest member of the group. Right now, the Sun’s largest planet is 445 million miles away. At that distance, it takes years to get there. Even so, nine spacecraft have traveled to Jupiter. Another mission is en route, with one more scheduled for launch next month.
Aldebaran is about 65 light-years away – more than 850,000 times farther than Jupiter. And Elnath is double that distance. That puts them far beyond our ability to reach them. Even so, they’re quite close as stars go. Our home galaxy, the Milky Way, spans a hundred thousand light-years. And all the other major galaxies are millions or billions of light-years away. So the Moon and tomorrow’s companions are all close neighbors – just down the cosmic block.
Script by Damond Benningfield
In many ways, fall has already arrived. The fall term has started for schools. Football season is underway. And September 1st marks the beginning of the fall weather season. Astronomical fall catches up to them tomorrow. Autumn officially arrives at 7:44 a.m. Central Daylight Time – the moment of the fall equinox.
The change in seasons occurs as the Sun crosses the equator from north to south. The Sun rises due east and sets due west as seen from the entire planet. And the length of day and night are about equal.
That balance won’t last long. In the northern hemisphere, the days will grow shorter and the nights longer until we reach the winter solstice, in December. As that happens, the sunrise and sunset points will slide southward.
As the season changes, so do the stars. At nightfall, Arcturus, the brightest star of summer nights, is dropping lower in the west. The signature star pattern of the season, the Summer Triangle, is moving to the western side of the sky. And the scorpion is getting ready to disappear in the southwest.
In the meantime, the Great Square of Pegasus is in the east at nightfall, ready to climb high across the sky during the night. Constellations associated with the flying horse are moving into view as well. And so are the constellations of the Celestial Sea – water-related constellations like the fish, the sea goat, and the water boy – stellar sights for the longer nights of autumn.
Script by Damond Benningfield
When Voyager 2 flew past Neptune, 35 years ago, its list of discoveries included six moons, a set of rings, a giant storm, and an odd magnetic field. Mission scientists converted some of its observations of the field to sound. And scientists are still trying to understand the magnetic field today.
Neptune is the Sun’s most remote major planet. It’s about four times Earth’s diameter. Methane in its upper atmosphere absorbs red light, giving the planet a blue-green color.
Neptune is tilted on its axis at about the same angle that Earth is. Also like Earth, its magnetic poles don’t line up with its geographic ones. But on Neptune, there’s a much bigger angle between the two – about 47 degrees, versus about 11 degrees for Earth.
And while Earth’s magnetic field is generated near the center of the planet, Neptune’s is generated closer to its cloud tops than its core.
Scientists haven’t settled on an explanation for how Neptune’s field is generated. It may be powered by “bubbling” motions inside a hot, slushy layer of ammonia, methane, and water. However it’s generated, Neptune’s magnetic field is powerful and complicated – befitting one of the giants of the solar system.
Neptune is at its best this week. It rises at sunset and remains in view all night, in Pisces. It’s brightest for the year as well. But it’s so far away that you need strong binoculars or a telescope to see it.
Script by Damond Benningfield
The giant planets of the outer solar system are like mini-solar systems on their own, because each has a large entourage of moons. Consider Neptune, the solar system’s fourth-largest major planet, which is putting in its best showing of the year. It rises at sunset and remains in the sky all night. It’s also at its brightest for the year. But it’s still so faint that you need a telescope to see it, in the constellation Pisces.
Until 1989, astronomers knew of only two moons orbiting Neptune. But 35 years ago, the Voyager 2 spacecraft discovered a half-dozen more moons as it flew past the planet. And since then, astronomers have used telescopes on the ground to find even more, bringing the total to 16.
Some of the moons probably formed with Neptune, four and a half billion years ago. But some of the more recently discovered moons may have been asteroids that were captured by Neptune’s gravity. And others may be fractured remains of a larger moon that split apart when it was hit by an asteroid or comet.
Neptune’s biggest moon may be a newcomer as well. Triton orbits in the opposite direction from most of Neptune’s moons, suggesting that the planet captured it in the distant past. And billions of years in the future, Triton will move so close to Neptune that the planet’s gravity will rip it apart. That will create a giant but short-lived ring around this giant planet.
More about Neptune tomorrow.
Script by Damond Benningfield
A hidden giant lurks between the Moon and the bright planet Saturn tonight. Neptune is the fourth-largest planet in the solar system, and it’s putting in its best showing of the year this week. But it’s so far away that you need help to see it.
Neptune is about four times the diameter of Earth. But it’s the Sun’s most-remote major planet – 30 times farther from the Sun than Earth is. As a result, it looks faint. It’s so faint, in fact, that it wasn’t discovered until September of 1846. And it was found because astronomers calculated that another planet was pulling on Uranus, the most-distant planet known at the time.
This week, Neptune is at opposition – it lines up opposite the Sun in our sky. That means it rises around sunset and is in view all night. The planet’s also closest to us for the year, so it shines at its brightest.
It peaks at a magnitude of about 7.7. That sounds bright. But in the magnitude scale, brighter objects have lower numbers. So Neptune would have to be several times brighter to be visible to the unaided eye even under the absolute best viewing conditions. Under moonlight or city lights, it would have to be even brighter.
Tonight, Neptune is to the upper right of the Moon at nightfall. It’s about half way along toward Saturn, which looks like a bright star. Neptune is a big but faint target for good binoculars or a small telescope.More about Neptune tomorrow.
Script by Damond Benningfield
The Moon has a lot going on tonight. For one thing, it’s full. And it’s the best-known full Moon of the year – the Harvest Moon. It’ll stage a minor eclipse that’ll be visible across almost all of the United States. And a couple of giant planets lurk near by – one of them especially close.
The Harvest Moon honor goes to the full Moon that’s closest to the fall equinox. The equinox is coming up on Sunday – just five days after the full Moon.
The lunar eclipse begins at 7:41 p.m. Central Daylight Time. That’s when the Moon makes contact with Earth’s outer shadow. But that part of the shadow is so faint that it’s hard to tell much difference.
A couple of hours later, the Moon will barely dip into the darker inner shadow. It’ll cover only a tiny fraction of the Moon, so it’ll look like something took a nibble from the disk. At least part of the eclipse will be visible from the entire United States except western Alaska.
Not long after the eclipse ends, the Moon will stage its own eclipse: It’ll pass directly in front of Neptune, briefly blocking the planet from view for most American skywatchers. Neptune’s too faint to see without binoculars or a telescope, so most of us won’t even notice it. We’ll have more about Neptune tomorrow.
And if all that lunar activity isn’t enough, the planet Saturn stands close to the Moon all night. It looks like a bright star – leading the Harvest Moon across the night sky.
Script by Damond Benningfield
On March 2nd of the year 1105, the Moon barely dipped its toe into Earth’s outer shadow, the penumbra. The eclipse was so faint and short that it probably went unnoticed. But it marked the start of a cycle that will last 1300 years and feature 73 eclipses. And the next one takes place tomorrow night. The full Moon – the Harvest Moon – will pass through the penumbra, and barely touch the darker inner shadow, the umbra.
Eclipses occur in cycles known as Saros. This eclipse is part of Saros 118.
The Moon starts a cycle at the far north or south of our planet’s shadow. Over the centuries, it moves through the shadow, until it exits at the opposite pole. So a Saros begins with penumbral eclipses, then moves through partial eclipses, total eclipses, then back again. The next eclipse in this Saros will take place in September of 2042.
This eclipse is number 52 in the series. It’ll begin at 7:41 p.m. Central Time, when the Moon first touches the penumbra. Later, the Moon will barely dip into the umbra, so it’ll look like a celestial dragon took a tiny nibble from the Moon. At least part of the eclipse will be visible from the entire United States except western Alaska.
So look for the almost-full Moon tonight, with the bright planet Saturn close by. Then tomorrow night, see if you can follow the subtle shading of a faint lunar eclipse.
Script by Damond Benningfield
If Planet Nine exists, it’s taunting astronomers. Several studies of the orbits of small bodies far from the Sun hint at the presence of a massive planet in the outer solar system. Yet the possible world has remained hidden.
Planet Nine was suggested in 2014, based on the orbits of some big chunks of rock and ice beyond the orbit of Neptune, the Sun’s most-distant major planet. The orbits appear to be influenced by the gravity of a body many times as massive as Earth.
The most recent evidence of Planet Nine comes from a study that modeled the orbits of 29 objects beyond Neptune. All of the orbits are tilted and stretched out. At their closest, these objects pass just inside the orbit of Neptune, which is 30 times farther from the Sun than Earth is. But they average more than a hundred times the Earth-Sun distance, so it takes many centuries for them to orbit the Sun.
Astronomers calculated the likelihood of so many objects following similar paths under two scenarios. In one, they modeled the gravitational effects of the Sun’s known planets, plus the pull of the rest of the galaxy’s stars and gas clouds. In the other, they added the effects of a possible Planet Nine. The model with Planet Nine produced a far better match to the orbits.
So far, a search of observations made along the planet’s possible path has come up empty. So if Planet Nine exists, it’s playing a game of hide-and-seek far from the Sun.
Script by Damond Benningfield
Comets are some of the most beautiful objects in the cosmos – balls of ice and rock with tails that can stretch for millions of miles. But they’re also some of the most fickle objects in the cosmos – they don’t always meet expectations. And some fall apart – vaporized by the Sun.
All of that is a preamble to the story of Comet C/2023 A3 Tsuchinshan-Atlas. Over the next few days, it might be visible through binoculars in the dawn sky, mainly from more southerly latitudes. And it could shine even brighter in the evening sky next month. Because we record our programs in advance, though, we can’t tell you how closely it’s matching the forecasts.
The comet was discovered last year. And early predictions called for it eventually to shine as brightly as Venus, which is climbing into view as the “evening star.” It’s no longer expected to get that bright. But it still could become bright enough to see with the eye alone.
The comet will pass closest to the Sun late this month, and closest to Earth next month – about 44 million miles away.
Now, the comet is passing through the constellation Sextans. That makes it a better target for skywatchers in the southern hemisphere. It’ll be easier to see from the northern hemisphere in the latter half of October, when it’ll climb fairly high at nightfall. So keep your eyes open – and your fingers crossed – for a good showing from a comet.
Script by Damond Benningfield
Two important sky paths intersect on the eastern and western horizons as night falls now: the ecliptic and the celestial equator.
The ecliptic is much easier to trace. It marks the Sun’s path across the sky. That path held great significance for many cultures, so they gave extra weight to the constellations it crossed – the constellations of the zodiac.
As night falls, the ecliptic arcs near a couple of the zodiac’s more prominent star patterns. It passes close above the “teapot” outlined by the stars of Sagittarius. And it nicks the “head” of Scorpius, with most of the scorpion’s body below it.
The Moon and planets all stay close to the ecliptic as well. As twilight fades this evening, for example, brilliant Venus is quite low in the west, with fainter Saturn about the same height in the east.
The equator is harder to see. It’s the projection of Earth’s equator on the sky, so it divides the sky into northern and southern hemispheres. Its closest bright star in early evening is Altair, which is high in the southeast. It’s in the northern half of the sky.
The equator maintains the same angle across the sky every hour of every day. But the ecliptic changes position as the night rolls on. It also shifts position from day to day. The two paths intersect along the horizon at some time during every day of the year. But they come together at nightfall only a couple of times a year – near the fall and spring equinoxes.
Script by Damond Benningfield
One popular sci-fi trope is invasion by alien “bugs” – microscopic organisms from other worlds that could harm life on Earth. But scientists also are concerned about things working the other way around: Earth bugs contaminating other planets. So landers are sterilized to prevent them from carrying any hitchhikers. And when the life of an orbiter ends, it’s targeted to crash into a place where it won’t cause any harm.
One world where that’s not a concern is Mercury. The Sun’s closest planet has no air – only a few atoms captured from the solar wind, or knocked off the surface of Mercury by the solar wind. And even that is a hard vacuum by Earth standards.
Mercury is zapped by solar energy. That heats the dayside to as high as 800 degrees Fahrenheit. And ultraviolet energy would destroy any Earth-like microbes.
So when the only Mercury orbiter to date wrapped up its mission, in 2015, it was allowed to crash into the planet.
The next Mercury mission is scheduled to fly past the planet next week, and enter orbit late next year. It may crash into Mercury when its mission is through as well – gouging a new crater, but leaving the planet uncontaminated.
Mercury is just creeping into the dawn sky. It looks like a fairly bright star. But it’s so low that you need a clear horizon to spot it. It’ll be a bit easier to see tomorrow because it’ll perch close to the right of the “fingernail” crescent Moon.
Script by Damond Benningfield
Star clusters are packed with stars, but not with planets. So far, only a few dozen of the more than 5600 confirmed exoplanets have been found in clusters. And two of those orbit a single star, in the Beehive Cluster.
The dearth of planets could simply mean that planets are hard to find. Only a small fraction of the stars in the Milky Way Galaxy reside in clusters, and not many clusters are close to us. And clusters can be tightly packed, making it hard to study their individual stars.
But because the stars are so tightly packed, it might be hard to make planets. As stars fly past each other, their gravity could stir up the raw materials for making planets, blocking their birth. And even when a planet is born, a close encounter could kick it away from its star. So maybe there really aren’t many planets in clusters.
The star in the two-planet system in the Beehive is a little smaller and cooler than the Sun, and four billion years younger. One of its planets is about twice the mass of Jupiter, the giant of our own solar system. And it’s so close to the star that it’s extremely hot. The other planet is even bigger, but much farther from the star, so it’s quite cold. So neither planet is a likely home for life.
The system is too faint to see without a telescope. But the Beehive is visible. Under dark skies, it looks like a hazy patch of light. At dawn tomorrow, it’s close to the right or upper right of the Moon.
Script by Damond Benningfield
No matter which system you go by, the names of the two brightest stars of Gemini aren’t quite right.
In mythology, the stars are named Pollux and Castor. They represent a pair of twin half-brothers. They had the same mother, but one had a mortal father, while the other was the son of Zeus, the king of the gods of Olympus. But the stars don’t look like twins. Pollux is almost twice as bright as Castor, and it looks orange, versus Castor’s pure white. They were called the twins mainly because they’re both bright, and they appear close together.
The stars themselves aren’t physically related. And they’re nothing alike. Pollux consists of a single giant star, while Castor is a system of six stars.
A second naming system is also off. In this system, Castor is Alpha Geminorum, while Pollux is Beta Geminorum.
The naming system was devised by Johann Bayer. In a star atlas published in 1603, he assigned each star to a constellation. And he named the stars using the letters of the Greek alphabet. “Alpha” usually was applied to a constellation’s brightest light, and “Beta” to the second-brightest. But in Gemini, they’re reversed. No one is quite sure why that’s the case. No matter the reason, though, the names of the bright “twins” of Gemini are a bit off.
The stars appear near the Moon early tomorrow. Pollux stands above the Moon at first light, with Castor a little farther to the upper left of the Moon.
Script by Damond Benningfield
When a delivery truck drops off its final package of the day, it isn’t abandoned – it’s prepped for more deliveries the next day. And it’s the same thing with several spacecraft. After delivering their main cargo, they’ve been given new missions – new addresses to check out.
The list has included three craft that delivered samples to Earth – bits of two asteroids, and some dust from a comet. The craft dropped capsules containing the samples into Earth’s atmosphere as they flew by. And another craft fired a cannonball into a comet.
After finishing their main missions, the spacecraft were still working. So they were given new missions. One of them is headed for a rendezvous with the asteroid Apophis, which will skim just above Earth in 2029. Another is headed for a comet.
Along the way, some of the missions have turned their cameras toward star systems with known planets. The craft can stare at a system for days or weeks. That allows them to measure tiny dips in a star’s light as a planet passes in front of it. Astronomers piece that together with information from other sources to refine a planet’s dossier – its size, mass, distance from its star, and more. One craft even found evidence of a second planet in a system, although it hasn’t been confirmed.
So even though some of these missions have long since dropped off their packages, they’re still delivering important discoveries about the universe.
Script by Damond Benningfield
Giant spiders crawl around the walls of an ancient city on Mars. And if that doesn’t sound like the plot of a bad movie, then what does? It turns out, though, that this plot is true – in a way. The “city” consists of walls of volcanic rock or hardened sand. And the “spiders” are explosions of dark dust from below the surface.
The region is called Inca City. It was discovered in 1972, in pictures from a Mars orbiter. It’s a grid of intersecting lines that resembles the outline of an ancient Incan city. The walls are miles long and hundreds of feet tall.
Scientists aren’t sure what created the lines. They could be hardened sand dunes. The most recent idea says they’re volcanic rock. Inca City may lie inside an old impact crater. Molten rock could have bubbled up through cracks in the crater floor. The floor was covered up, but the Martian winds have swept it clean, exposing the ridges.
Inca City is near the edge of the southern polar ice cap. Frozen carbon dioxide covers the region in winter. In spring, it vaporizes. Carbon dioxide a few feet below the surface can vaporize first, blowing holes in the ice above it. Dark dust in the plumes then settles to the surface – forming “spiders” around the walls of Inca City.
Look for Mars before and during dawn now. It looks like a bright orange star. Tomorrow, it’s to the upper right of the crescent Moon. The brilliant planet Jupiter stands above them.
Script by Damond Benningfield
The Moon and three other bright lights form a beautiful diamond in tomorrow’s dawn sky. Going clockwise from the Moon, the points of the diamond are the planet Jupiter, which is the brightest of the three; the planet Mars; and the star Elnath, the tip of one of the horns of Taurus.
The Sun illuminates about a third of the side of the Moon that’s facing our way. The most prominent feature in the sunlight is a giant dark patch known as the Ocean of Storms. It’s one of the largest features on the Moon. It covers one and a half million square miles – about one-tenth of the Moon’s entire surface.
A half dozen probes have landed in that vast region, including the Apollo 12 mission in 1969.
The most recent lander was Chang’e 5. The Chinese mission brought about four pounds of rocks and dirt back to Earth, in 2020. The samples indicated that the “ocean” formed about two billion years ago, when the Moon was about half of its current age. That makes the Ocean of Storms the youngest of the Moon’s big volcanic plains.
The feature may have formed when molten rock pushed its way to the surface through long, wide cracks. But the origin is still being debated. Some scientists say it formed after a massive asteroid slammed into the Moon. The impact gouged a wide crater that later filled with lava – forming a giant “ocean” on the Moon.
The Moon will stand close to Mars on Wednesday; more about that tomorrow.
Script by Damond Benningfield
The Sun has been feisty this year. It’s produced some monster storms that have pelted Earth with radiation and charged particles. That’s disrupted some communications, air travel, and other daily activities.
There’s evidence that the Sun has been much feistier in centuries past. If such major outbursts happened today, they could be really bad for modern technology. But the big ones in the past are good for archaeology. They’re helping scientists nail down the dates of some ancient human activities.
The Sun is especially active every 11 years or so. It blasts out giant clouds of charged particles. When the particles hit the atmosphere, they create cascades of other particles. That includes a radioactive form of carbon. Trees take up some of this carbon. The more active the Sun is, the more they absorb.
By analyzing the ratio of different forms of carbon in tree rings, scientists can determine which years were especially “stormy.” And that gives them a way to date human settlements.
Earlier this year, for example, a team studied rings in logs that were used to make houses and other structures at a site in Greece. The scientists found rings that recorded a busy year for solar activity. It corresponded to a previously discovered peak, in 5259 BC. Counting all of the tree rings showed the site had been inhabited for at least a couple of hundred years – including a time with an especially feisty Sun.
Script by Damond Benningfield
Stars aren’t always what they seem. Consider the two brightest stars of Lyra. The constellation’s leading light is Vega. It looks 20 times brighter than the second-ranked star, Sulafat. But that’s only because Vega’s much closer. If you lined them up at the same distance, Sulafat would look 60 times brighter than Vega.
The difference is caused by their stage in life. Vega’s in the prime of life. It’s “fusing” the hydrogen atoms in its core to make helium, releasing energy in the process. Vega is more massive than the Sun, so those reactions happen at a much faster rate – making Vega about 40 times brighter than the Sun.
Sulafat has moved into the next stage of life. It’s converted the hydrogen in its core to helium. Now, it’s fusing hydrogen in a thin layer around the core. That’s caused its outer layers to puff up, helping the star shine about 2400 times brighter than the Sun.
Eventually, Sulafat will start fusing the helium in its core. That’ll make it even bigger and brighter. Then it’ll shed its outer layers, leaving only its dead core. Vega will experience the same fate – more than a billion years from now.
Lyra is high overhead at nightfall. It’s easy to spot because Vega’s one of the brighter stars in the night sky. Four stars outline a tilted, flat box to the lower right of Vega. Sulafat is at the corner of the box that’s farthest from Vega.
Script by Damond Benningfield
In the early 20th century, much of the world had “Mars fever.” Percival Lowell had mapped what he called “canals” on Mars, built by a dying civilization. H.G. Wells published “War of the Worlds,” about a Martian invasion. Inventor Nicola Tesla reported hearing possible signals from Mars. So there was a lot of interest in the Red Planet. In 1901, Richard Taylor wrote this march to capture the enthusiasm – “A Signal From Mars.”
People listened for signals 100 years ago this week. Mars was passing especially close to Earth. Astronomer David Todd thought Martians might try to contact us. So he organized a campaign to listen for radio transmissions.
Among others, he worked with Charles F. Jenkins, who’d built a device that could transmit photographs via radio. Jenkins later developed early forms of television.
Starting on August 21st, 1924, Jenkins recorded radio waves on a roll of photographic paper whenever Mars was in the sky – more than 20 hours in all. Todd said he saw faces in the squiggles on the paper. But Jenkins thought it was nothing but noise.
Technicians at some radio stations reported hearing odd sounds during the hunt. Most of the sounds came from Earth, although some might have been natural radio waves from astronomical objects.
But none of them came from the Red Planet. There were no signals from Mars.
Script by Damond Benningfield
Jupiter stands high in the east at daybreak. It’s the brightest point of light in the sky at that hour, so you can’t miss it.
Jupiter’s moon Io is the most volcanic world in the solar system. But some planets in other star systems could give Io some competition. Their daysides could feature hundreds of giant volcanoes, and be paved with molten rock.
One example is LP 791-18d. It’s about the same size and mass as Earth. It orbits a small, cool star. But it’s so close to the star that its surface is extremely hot. And it’s made even hotter by the gravitational tug of two other worlds. They squeeze and stretch the planet’s interior, heating it enough to create volcanoes.
A recent study says that volcanic gases could form an atmosphere. As the air circulates to the nightside, water could condense and fall to the surface – perhaps making that side an abode for life.
Webb Space Telescope recently found evidence of a thick atmosphere around another volcanic world, HD 104067d. The planet is bigger and heavier than Earth. Like the other volcanic planet, it’s quite close to its star. And it’s tugged by the gravity of other planets in the system, heating its interior and forming volcanoes.
Its atmosphere appears to carry a lot of heat from the dayside to the nightside. So the planet isn’t a likely home for life – a hellish world of giant volcanoes.
Tomorrow: helping hands.
Script by Damond Benningfield
The stars of the Summer Triangle look a lot alike. Vega, Deneb, and Altair are among the 20 brightest stars in the night sky, and they all shine almost pure white. Vega and Altair really are alike. But except for the way it looks to our eyes, Deneb is nothing like the other two.
The triangle is high in the eastern sky at nightfall. It’s easy to see even through the glare of the almost-full Moon. Vega is the highest and brightest of the three stars. Deneb stands to the lower left of Vega, with Altair farther to the lower right.
Vega and Altair are both about twice the size and mass of the Sun, and a good bit brighter. And both of them spin rapidly – so fast that they bulge outward at the equator. Vega is farther along in its evolution than Altair is. Because of their mass, both stars will spend about a billion years in the “prime” phase of life. That’s compared to about 10 billion years for the Sun.
Deneb is a supergiant – one of the bigger and heavier stars in the galaxy. Some of its details are unclear because its distance is uncertain. It could be about 1500 light-years away, or about 2600. Either way, we know that it’s about 20 times the mass of the Sun, and up to 200 thousand times the Sun’s brightness. It’s no more than 10 million years old, with almost no time left. Before long, it’ll explode as a supernova, then fade away – and the Summer Triangle will disappear.
Script by Damond Benningfield
As far as we know, there are no giant ants at IRAS 2A, an embryonic star system almost a thousand light-years away. But the system does contain the compound that makes an ant sting hurt: formic acid.
It’s one of dozens of complex molecules found in young star systems across the galaxy. The list includes such well-known molecules as ozone, cyanide, formaldehyde, methane, and ethanol. Many of the compounds are key ingredients for life, such as tryptophan – an amino acid that’s essential for making proteins in the human body.
Scientists aren’t sure just how these molecules take shape. One suggestion says they form through chemical reactions on small ice grains found in the cloud of material that encircles a young star. And recent observations of IRAS 2A and other young stars by Webb Space Telescope seem to support that idea.
IRAS 2A consists of two “protostars” – objects that are becoming stars but aren’t quite there yet. Each of them appears to be about half as massive as the Sun. They’re surrounded by a disk of debris – gas, dust, and ice, with a dollop of complex organic molecules. If the system gives birth to any planets, those molecules could help make the worlds habitable – and perhaps provide ingredients for life itself.
IRAS 2A is in a star cluster in Perseus. The cluster climbs into view, in the northeast, by midnight. But it’s too faint to see without a telescope.
Script by Damond Benningfield
50 years ago this summer, astronomers Russell Hulse and Joseph Taylor went pulsar hunting. And they bagged a real trophy – a binary system that contained a pulsar and another dead star. The discovery, and their later analysis of the system, earned Hulse and Taylor the 1993 Nobel Prize in Physics.
Both members of the binary are neutron stars – the crushed cores of once-mighty stars. Each is about 1.4 times the mass of the Sun, but only about as big as Earth. One of the stars rotates rapidly, sending out “pulses” of energy at each turn like a cosmic lighthouse. That makes the star a pulsar.
It spins about 17 times per second. But the timing changes ever so slightly as the stars orbit each other. The changes have revealed that the stars are spiraling closer together – by about three millimeters per orbit.
The stars are getting closer because they’re losing energy – by producing ripples in space and time known as gravitational waves. They were predicted by Albert Einstein’s theory of gravity. But the binary star system provided the first evidence that the waves actually exist.
The two stars should slam together in a few hundred million years, producing a torrent of gravitational waves. In August of 2017, in fact, a gravitational-wave observatory “heard” the merger of another pair of neutron stars – more confirmation that Einstein’s theory of gravity was right.
Script by Damond Benningfield
Our Sun has been doing the same thing for the past four and a half billion years – converting the hydrogen in its core to helium, producing huge amounts of energy in the process. And it’ll keep on doing that for billions of years more.
Over the eons, that slow, steady change produces major consequences: The Sun gets bigger and brighter as it ages. That trend has important consequences for Earth and the other planets.
As a star converts more and more hydrogen into helium, the core shrinks. That squeezes the core, which makes it hotter. That revs up the rate of nuclear reactions, which increases the amount of energy produced in the core. That energy pushes outward on the surrounding layers of gas, making the star expand. It also increases the total amount of energy the star radiates into space, making it brighter.
Models of how stars evolve say the newborn Sun probably was only about 70 percent as bright as it is now. But that creates some problems. Studies show that Mars was much warmer in the distant past, for example. But if the Sun was fainter, that shouldn’t be the case – the young planet should have been a desolate iceball.
In the future, the Sun will continue to get brighter, which is bad news for Earth. In a billion years or so, our star will be about 10 percent brighter than it is now. That extra energy may be enough to vaporize the oceans – turning our planet into a burned-out cosmic cinder.
Script by Damond Benningfield
The Moon creeps up on the bright star Antares this evening. Depending on your location, you might see them pass less than a degree from each other – less than the width of your finger held at arm’s length. Because the Moon will be so close to Antares, it’ll wash out the star’s reddish orange color.
Astronomers have been tracking that color for thousands of years. And they haven’t seen much change.
Antares is a red supergiant – it’s many times bigger and heavier than the Sun, and tens of thousands of times brighter. Its surface is thousands of degrees cooler than the Sun’s, which is why it looks red.
On the inside, supergiant stars are changing in a hurry – fusing lighter elements to make heavier ones. But the change isn’t always reflected at the surface. In a study a couple of years ago, a team of scientists found that the color of Antares has remained pretty steady for at least 3300 years.
The team analyzed observations from Europe, the Middle East, and China. In China, the star was known as “Great Fire.” In Egypt, it was “red one of the plow.” And many records compared the star to Mars, which is known for its reddish color. In fact, the name “Antares” means “rival of Mars” – a comment on their similar appearance.
The study said the star’s unchanging color could mean that Antares has a good run left before it explodes as a supernova – another million years or longer.
Script by Damond Benningfield
The Moon “shines” by reflecting sunlight. But it’s not a great mirror – it reflects only about one-tenth of the sunlight that strikes it. So it’s actually quite dark.
Even so, it reflects enough radio waves that it served as the first communication satellite. In the late 1950s and early ’60s, the United States Navy used the Moon to relay signals between bases, and to some ships at sea.
That developed from an earlier project that listened for radar transmitted from inside the Soviet Union. Originally called Project Joe, it started in 1947, after the Army successfully bounced its own radar waves off the Moon. It began regular operations 75 years ago this month.
Early results were better than expected, so the Navy began studying how to use the Moon to send signals, not just receive them.
At the time, it maintained long-range contact by bouncing radio waves off the ionosphere – an electrically charged layer of the atmosphere. But storms on the Sun could interrupt transmissions. The Moon would be more reliable. In 1954, project leader James Trexler beamed his own voice to the Moon and back. And by late 1960, the system was in regular use – bouncing radio waves off the Moon.
The Moon is just past first quarter tonight, so the Sun lights up a bit more than half of the lunar disk. The bright star Antares is well to the upper left of the Moon. More about the Moon and Antares tomorrow.
Script by Damond Benningfield
Mars and Jupiter are staging an especially close encounter in the early morning sky. They climb into good view by 2 or 2:30, and stand high in the east at dawn, so you shouldn’t have any trouble finding them.
Jupiter is by far the brighter of the two. In fact, it’s the brightest object in the early morning sky now other than the Moon. It shines almost 20 times brighter than Mars. But the Red Planet is pretty bright on its own. And it’ll only get brighter as the year progresses.
That’s because Mars and Earth are moving closer to each other. Earth is the third planet from the Sun, while Mars is the fourth. Since we’re closer to the Sun, we move faster than Mars does. So every 26 months, we catch the Red Planet, then move past it.
Right now, we’re in chase mode, closing the gap by a little bit each day. As we get closer, Mars gets brighter. By the end of the year, it’ll shine about eight times as brightly as it does now. It’ll reach its peak in mid-January, when Earth passes Mars and the two planets are at their closest.
For now, watch for Mars as it slips past Jupiter the next few mornings. It stands a little above Jupiter tomorrow. They’ll be closest on Wednesday and Thursday, separated by a fraction of a degree – less than the width of a pencil held at arm’s length. After that, they’ll move apart, with Mars lagging behind its brighter sibling.
Tomorrow: messages from the Moon.
Script by Damond Benningfield
Starlight sprinkles down on Earth like raindrops in a summer shower. And like raindrops, the sprinkles of starlight can appear to change direction.
This effect is known as aberration of starlight. It was discovered three centuries ago by an astronomer who was trying to measure the distance to Eltanin, the brightest star of Draco, the dragon.
James Bradley was looking for the star’s parallax. The idea is to observe a star when Earth is at opposite sides of its orbit. That causes stars that are close to us to shift position relative to stars that are farther away. Measuring the size of that shift reveals the star’s distance.
Bradley did see a shift in Eltanin’s position. But it wasn’t related to the star’s distance. Instead, it was caused by Earth’s orbital speed. The effect is like watching raindrops fall from inside a car. If you’re sitting still, the raindrops might appear to fall straight down. But if you’re cruising down the highway, they appear to come toward you at an angle. The raindrops aren’t moving any differently – you are.
The same thing happens with starlight. Thanks to Earth’s motion around the Sun, the “drops” of light appear to come in from different angles at different times of year. That causes a star to appear to shift position – the result of the aberration of starlight.
Eltanin is high in the north-northeast at nightfall. The moderately bright star stands to the left of brilliant Vega.
Script by Damond Benningfield
Different stars face different fates. The smallest will shine feebly for trillions of years – many times longer than the current age of the universe – then simply fade away. The heaviest, on the other hand, will blast themselves to bits, briefly shining brighter than billions of normal stars.
A bright star that faces such a violent end is in good view tonight. Spica stands to the upper left of the Moon as night falls.
Spica actually consists of two stars.
The heavier star, Spica A, is about 10 times the mass of the Sun. Such stars burn through their nuclear fuel in a hurry. That makes them extremely bright. But it also means they won’t live long. For Spica A, the prime of life will last for less than 30 million years, compared to about 10 billion years for the Sun. When the star can no longer produce nuclear reactions in its core, the core will collapse. The star’s outer layers will fall inward, then rebound at a few percent of the speed of light. That’ll blast the star apart as a supernova.
Its companion, Spica B, is about six times the Sun’s mass. If it survives the supernova, it’ll live more than a hundred million years. At the end of its lifetime, it’ll swell up to many times its current size, just as Spica A will. But it’s not massive enough to explode. Instead, it’ll lose its outer layers in a less-violent process. That’ll leave only its dead core, shining faintly through the long cosmic night.
Script by Damond Benningfield
Today, it’s hard not to know the time. Your phone, your TV, your car, and scads of other devices give you the time, accurate to a tiny fraction of a second. But in ages past, telling time wasn’t that easy – especially at night. Fortunately, nature provided a decent nighttime “clock”: the stars. The location of certain stars at different times of year told skywatchers the time of night.
A prime example of how that worked comes from ancient Egypt.
The Egyptian day was divided into 24 hours – a system passed along into modern times. Daytime and nighttime each consisted of 12 hours, regardless of the time of year. So the length of an “hour” varied between night and day, and from season to season.
The nighttime hours were marked by prominent stars. The gap between either the setting times or rising times of two of these stars marked an hour. And each star “reigned” for about 10 days before the next one took its place. So the Egyptian year was divided into 10-day “weeks,” known as decans – 36 in all. An extra five days were added to the end of the year, bringing the calendar to 365 days.
The year began with the first dawn appearance of the star Sirius, the brightest star in all the night sky. It marked the start of the annual flooding of the Nile River, which brought renewed life to the fields – an event marked by the “ticking” of the starry clock.
Script by Damond Benningfield
The Milky Way has played a key role in the lore of many cultures. Among other things, it’s represented a road, a river, and the path of the dead into the afterlife – and their home in the afterlife.
The role of the Milky Way in ancient Egypt is still a bit – well, milky – it’s just not clear. But some studies have suggested that it represented the sky goddess Nut. And some recent work says the summer Milky Way represented her backbone, while the winter Milky Way represented her arms.
Nut was depicted as a star-covered woman arched across the sky. She protected the earth – her brother and consort, Geb. And she was supported by the air – their father, Suh.
During the day, the Sun-god Re sailed across her back. At sunset, Nut ate the Sun as it disappeared in the west. At dawn, she gave birth to the Sun, allowing it to return to view in the east. She played a similar role in the motions of bright stars that were used to track time; more about that tomorrow.
The recent study says that Nut represented the entire sky, not just the day. So she arched over the nighttime as well – helping protect the Sun and stars during their trip through the underworld. But the Milky Way changes orientation during the night and during the year. So it doesn’t always align with the rising and setting Sun. The alignment is best during parts of summer and winter – the Sun and Milky Way in harmony – connected by the sky goddess.
Script by Damond Benningfield
Sirius is the brightest star in the night sky. And it’s just starting to peek into view in the dawn twilight. It’s easier to pick out as you go farther south.
It’s especially easy to see from Cairo and southward along the Nile River. In ancient times, the star played a big role in Egypt’s religion and its daily life.
Egyptians called the star Sopdet – a name that means “skilled woman” – after a goddess of life and fertility. She was the sister and wife of the god Sah, who was represented by the stars of Orion. Eventually, she became identified with the goddess Isis.
The star Sopdet was an important calendar marker. Its first appearance in the dawn indicated that the annual flooding of the Nile was about to begin. The flood brought water and fresh soil to the fields, making them fertile for another year. So Sopdet’s return to view was so important that it marked the beginning of the year. The occasion was celebrated with a festival – “the Coming of Sopdet.”
At first, that all happened in June, around the beginning of summer. Today, though, Sirius doesn’t climb into view until August. That’s because Earth wobbles on its axis, causing the stars to move across the seasons – shifting Sopdet away from its honored position.
Look for Sirius quite low in the southeast as twilight brightens. If you can’t see it quite yet, be patient – it’ll be in view from the entire country by the end of the month.
Script by Damond Benningfield
Venus is just beginning a slow climb to prominence as the “evening star.” It’s quite low in the west at sunset and sets not long afterward, so it’s hard to spot. Tonight, it’s close to a slightly easier target – the crescent Moon. Even so, you need a clear horizon and good timing to see either one.
Venus and the Moon may have something in common: Both of them might have been involved in “big whacks” when the solar system was young.
There’s a pretty good chance that the young Earth was hit by a body as big as Mars. That blasted out a huge amount of material. Much of it coalesced to form one or more moons – including the one we see today.
It’s possible that Venus got a big whack as well. The impact made Venus spin in the opposite direction from most of the other planets in the solar system. As seen from above, Earth and most of the other planets rotate counterclockwise – the same direction in which they orbit the Sun. Venus also orbits counterclockwise, but it rotates clockwise.
When Venus was born, it probably spun in the same direction as the other planets. So something might have hit the young planet. The impact either flipped it upside down or caused it to reverse direction. The blast might also have created a moon. But unlike our moon, it didn’t survive.
Look for Venus and the Moon shortly after sunset, quite low in the west. The view is better as you go farther south.
Script by Damond Benningfield
A giant stellar nursery lies just 4500 light-years away. But the complex of brilliant stars and star-making materials is hidden – veiled by clouds of dust.
Cygnus X spans more than 600 light-years. It contains enough material to give birth to millions of stars as massive as the Sun. And it’s already spawned several thousand stars that are many times as massive as the Sun, and thousands of times brighter.
Astronomers study the region at wavelengths that shine through the dust. They reveal a complex web of ribbons, bubbles, rings, and pillars. They form several interlinked regions of starbirth.
A cluster of massive newborn stars is near the middle of the complex. They produce radiation and powerful “winds” that push and erode the surrounding gas and dust. That can stop the process of star formation. But it can also trigger the birth of new stars as it squeezes the gas and dust.
Especially heavy stars blow big bubbles in the gas. They also shape dense regions into pillars that can span dozens of light-years.
Cygnus X probably has been forming stars for the past 10 million years or so. But it’s just getting started – it’s likely to form tens of thousands more stars.
Cygnus X is in Cygnus, the swan, which is high in the east at nightfall. The complex is hidden behind dark clouds that run from the bright star Deneb, the swan’s tail, to Sadr, at the intersection of its long body and graceful wings.
Script by Damond Benningfield
Under a dark sky, the Milky Way is impressive – a milky band of light that outlines the disk of our home galaxy. But the band isn’t smooth. It’s lumpy, with some parts much wider and brighter than others. And a dark lane runs down its middle, bisecting the Milky Way into two bands. It, too, is lumpy.
That dark lane is known as the Great Rift, and it looks almost empty – as though a cosmic dragon has swallowed most of the stars. Instead, the darkness has simply swallowed the light of the stars behind it. That’s because the dark lane is made of giant clouds of dust. They block the visible light of the stars inside and behind them, just as a dark cloud here on Earth can block the Sun from view.
Perhaps the most famous cloud is the Coalsack, an especially big “hole” in the Milky Way. It’s in the Southern Cross, which is too far south to see from the continental United States. The Coalsack is about 600 light-years from Earth, and spans about 60 or 70 light-years.
There’s also the Northern Coalsack. It’s just about as big as the southern version, although it’s not quite as dark or well-defined. Still, there’s a definite gap in the stars there. It’s in Cygnus. As night falls now, it’s to the right of Deneb, the bright star that marks the swan’s tail.
The Northern Coalsack veils an especially bright region behind it – one of the biggest stellar nurseries in our part of the galaxy. More about that tomorrow.
Script by Damond Benningfield
For most Americans, the Milky Way is more of an idea than a reality. Light pollution blocks the view of the Milky Way and much more. So for most, the only way to see the Milky Way is to get out of town – to visit dark locations far from city lights.
Fortunately, there are still quite a few places where the skies are dark enough for the Milky Way to shine through. The International Dark Sky Association certifies many “dark-sky” locations – parks, towns, and even entire regions.
Such locations have taken steps to ensure that their skies remain dark. They use streetlamps that have a redder glow, which is less troublesome than blue light, for example. They ban certain types of outdoor lighting, and require that other types be shielded so their light goes down, not up.
There are about 140 certified sites in the United States. This year alone, the association has certified towns in Texas and Utah, a wildlife area in Michigan, and a large chunk of Oregon. The list includes many national parks, such as the Grand Canyon. And McDonald Observatory is inside one of the world’s largest dark-sky sanctuaries, in West Texas.
If you have nice, dark skies, tonight is a great time to look for the Milky Way. At nightfall, it arcs from the “teapot” of Sagittarius, in the south; through the swan, high in the east; and down to W-shaped Cassiopeia, low in the northeast – the magnificent glow of our home galaxy.
Script by Damond Benningfield
The hazy band of the Milky Way arches high across the sky on these mid-summer nights. At nightfall, it stretches from almost due north, high across the east, to almost due south. And it arcs high overhead by midnight. But you need to get away from city lights to see it.
The Milky Way is the combined light of millions of stars in the disk of our home galaxy. The galaxy’s busy core is in the teapot-shaped constellation Sagittarius, which is low in the southern sky at nightfall. We can’t actually see the core because it’s hidden behind clouds of dust, which form dark lanes within the Milky Way.
Astronomers use special instruments to peer through this dust. The instruments reveal some remarkable sights, including clusters of some of the hottest, brightest stars in the entire galaxy.
Two of the clusters are the Arches and the Quintuplet. Their stars probably formed just a few million years ago. Big clouds of gas and dust rammed together, triggering an intense bout of starbirth.
Many of the stars in these clusters are among the most massive in the galaxy. The heaviest is the Pistol Star. It’s probably more than a hundred times the mass of the Sun.
The cores of these massive stars are extremely hot, so the stars burn through their nuclear fuel in a hurry. Within a few million years, they’ll blast themselves to bits in titanic explosions. Even then, they’ll likely remain hidden from human eyes behind the cosmic haze.
Script by Damond Benningfield
Astronomers are about to need a really big photo album to store their new snapshots of the universe. That’s because their newest digital camera is ready to look skyward. Each image will consist of 3.2 gigapixels – almost a hundred times the size of the highest-resolution pictures on most smartphone cameras. It’s the largest camera ever for astronomy.
The camera was built for the Legacy Survey of Space and Time, which will use a giant telescope under construction in Chile. It will image the entire sky roughly once every two and a half nights.
Astronomers will use those observations to study dark energy and dark matter. They’ll find new asteroids and comets in the solar system – including some that might someday threaten Earth. They’ll look for stars that grow dimmer as their own planets pass in front of them. And they’ll look for exploding stars and other rapidly changing objects and events.
The new camera was built by a national laboratory in the United States. It’s as big as a small SUV and weighs about three tons. Its field of view will cover 40 times the area of the full Moon. The project will capture about 15 terabytes of data every night – the equivalent of more than a year of high-definition video or a couple of decades of music.
The project is set to begin sometime next year – compiling a huge album of pictures of the universe.
Tomorrow: the glory of the summer Milky Way.
Script by Damond Benningfield
On modern maps of the universe, every star belongs to a single constellation. But in ages past, some stars were known as connecting stars – they belonged to two constellations. And one of those stars is close to the Moon early tomorrow.
The star is Elnath. Its name means “the butting one” – a reference to its position at the tip of one of the horns of Taurus, the bull. In fact, a second name for the star is Beta Tauri – an indication that it’s the second-brightest star in the constellation.
But until almost a century ago, Elnath was also known as Gamma Aurigae. That name indicated that it was one of the brighter stars of Auriga the charioteer. And in many older star atlases, it’s depicted as part of the charioteer’s outline.
Until the early 20th century, there were no rules about where a star might belong – it could be a member of more than one constellation with no problem. In the 1920s, though, the International Astronomical Union tidied up the geography of the heavens. It designated 88 official constellations. And it defined precise boundaries for each one. So every star was given its own home in the cosmos – including Elnath, the horn of the bull.
Elnath stands close to the Moon at dawn. Three other bright lights form a triangle to the upper right of the Moon: Mars, at the top of the triangle; brilliant Jupiter, at the lower left; and Aldebaran, the bull’s eye, at the lower right.
Script by Damond Benningfield
The Moon and three bright companions form a figure that resembles the outline of a sail early tomorrow. Mars is close to the lower right of the Moon, and looks like a bright orange star. Much brighter Jupiter is farther below the Moon. And the star Aldebaran is to the right of Jupiter. It looks like a near-twin of Mars – almost exactly the same brightness and color.
Robotic ambassadors from Earth are studying three of the four bodies from close range – all but Aldebaran, which is 65 light-years away.
Several spacecraft are studying the Moon, with quite a few more scheduled for arrival over the coming year or two. The longest-lived current mission is Lunar Reconnaissance Orbiter. It’s been mapping the Moon for 15 years.
Only one mission is active at Jupiter. Juno entered orbit around the giant planet eight years ago. It’s studied Jupiter itself, plus several of the planet’s large moons.
And a whole bunch of missions are operating at Mars – orbiters and rovers launched and controlled by the United States, China, Europe, India, and the United Arab Emirates. Two of the orbiters have been operating for more than two decades. And the Curiosity rover has been trundling along the surface for 12 years.
The pace of Mars missions has slowed down. But several missions are in the planning stages – including some that would bring Martian samples back to Earth.
More about the Moon and its companions tomorrow.
Script by Damond Benningfield
The Moon dashes through a region packed with bright stars and planets the next few mornings. It’ll pass especially close to Mars, Jupiter, and Elnath, the tip of one of the bull’s horns. Aldebaran, the bull’s eye, will remain a little farther from the Moon.
The meetings occur near the ecliptic – the Sun’s path across the sky. The planets all stay close to the ecliptic as they move through the starry background. The stars are in fixed positions relative to the ecliptic, with Elnath and Aldebaran especially close to it. Finally, the Moon’s orbit around Earth is tilted a bit relative to the ecliptic, so the Moon stays close to that path as well.
The Moon sometimes occults Elnath or Aldebaran, passing in front of the star and blocking it from view. Aldebaran is about five degrees south of the ecliptic, while Elnath is about five degrees north. That puts the stars at the limits of the Moon’s path.
The Moon moves north and south of the ecliptic in cycles, so occultations come in groups. The next set of Aldebaran occultations won’t start until 2033. But for Elnath, the next cycle starts in September and continues into 2027. The Moon won’t occult either star this month, although it’ll come close to Elnath on Wednesday.
Tomorrow, look for these four bright objects aligning to the lower left of the Moon at first light. Jupiter is the brightest member of the quartet, with Mars ranking second. More tomorrow.
Script by Damond Benningfield
The center of the Milky Way Galaxy is already packed with stars. But in a few million years, tens of thousands more could flare to life in a region known as the Brick. It’s a vast cloud of cold, dark gas and dust that’s shaped like a brick.
It may be the biggest future star cluster in the entire galaxy. It’s more than a hundred thousand times the mass of the Sun. And observations in recent years have shown that it contains dozens of dense blobs of material – “cocoons” that could be giving birth to stars even now.
Stars are born when such blobs collapse under their own weight. As a blob collapses, it gets hotter. If it gets hot enough, nuclear fusion ignites in its core – giving birth to a star.
There are indications that a few small stars have already formed in the Brick. But such giant clouds are also where big, heavy stars are born – stars that shine tens of thousands of times brighter than the Sun.
It’s not certain that the Brick will give birth to many stars at all. While it has the right ingredients, it’s in the most crowded region of the galaxy. The gravity of the stars and clouds around it could keep it too stirred up to form stars. Powerful magnetic fields could hinder star formation as well.
Astronomers will study the Brick in more detail in the coming years to determine whether it’s the site of future fireworks – or a galactic dud.Tomorrow: dawn encounters for the Moon.
Script by Damond Benningfield
You’ll find lots of visitors in the downtown of any major city. That may also be the case with the “downtown” of our home galaxy, the Milky Way. A recent study found that one of the stars in the galaxy’s core probably was born far outside that region.
The core contains a supermassive black hole that’s more than four million times the mass of the Sun. Swarms of stars encircle the black hole – some of them quite close. But the black hole’s gravity is so powerful it would stir up any star-forming gas and dust around it, preventing the birth of stars. So the stars that are close to the black hole must have been born elsewhere, then migrated in toward the black hole.
One of those stars is cataloged as SO-6. The new study found that it’s no more than two-thirds of a light-year from the black hole, and perhaps a good bit closer.
The star is probably about 10 billion years old – twice as old as the Sun. And it’s nearing the end of its life – it’s gotten bigger and cooler, forming a red giant. That suggests it’s about the same mass as the Sun.
But its chemical composition doesn’t match that of most of the stars in the core. Instead, it’s a closer match for the stars in many of the small galaxies that surround the Milky Way. So SO-6 could have started 50,000 light-years or more from its current location, then migrated into the core – a visitor to “downtown” Milky Way.
Script by Damond Benningfield
The black hole at the center of the Milky Way Galaxy is a light eater – at least it is today. But 200 years ago, it could’ve had a feast. That would have made it shine hundreds or thousands of times brighter than it is today.
The black hole is called Sagittarius A-star. It’s more than four million times the mass of the Sun. That’s actually pretty small for a black hole in a galaxy as big as the Milky Way.
Like all supermassive black holes, it’s encircled by a disk of gas. Some of that material funnels into the black hole. As it does, it gets hot enough to shine at many wavelengths, including X-rays. How bright it gets depends on the mass of the disk – how much stuff the black hole is eating.
Today, the X-ray glow is fairly steady, but faint. But a space telescope has detected some X-ray-bright areas a couple of hundred light-years from the black hole. Those areas could have been illuminated when the black hole flared up about 200 years ago. The black hole might have wolfed down an unlucky asteroid or a small cloud of gas and dust – a feast for the black hole, accompanied by a short but bright flare-up.
The black hole is in Sagittarius, which is in the southern sky on summer evenings. Its brightest stars form the outline of a teapot. The black hole is above the spout of the teapot, but it’s hidden behind clouds of dust – 27,000 light-years away.
More about Sagittarius tomorrow.
Script by Damond Benningfield
Sagittarius has a bit of an identity crisis. It’s easy to see – just not as what it’s supposed to be. In mythology, Sagittarius was known as the archer. But that title doesn’t tell the whole story. He was actually a centaur – a creature with the head and torso of a man, but the body and legs of a horse. He was holding a bow, however – aimed at the nearby scorpion.
To modern eyes, though, the constellation looks like something a little less fearsome: a teapot. It’s low in the south-southeast at nightfall, with the handle to the left and the spout to the right. If you have even moderately dark skies, it’s not hard to find.
Sagittarius lies along the glowing band of the Milky Way – millions of stars that outline the disk of the Milky Way Galaxy. And the constellation contains the brightest part of the Milky Way – the Large Sagittarius Star Cloud. It appears to rise from the spout of the teapot like a cloud of steam. It’s so bright because it’s toward the center of the galaxy, so we’re looking through a thick layer of stars.
The center itself is concealed behind clouds of light-absorbing dust. So we don’t see the full glory of the Milky Way’s core. Astronomers use instruments that are sensitive to infrared and other wavelengths to see through the dust.
The core also contains a supermassive black hole – a monster that’s more than four million times the mass of the Sun. We’ll have more about that tomorrow.
Script by Damond Benningfield
The fat gibbous Moon creeps up on the planet Saturn tonight. Saturn is to the lower left of the Moon as they climb into good view, before midnight, and looks like a bright star.
If you remove its beautiful rings, Saturn itself looks a bit bland – like a slightly flattened beachball colored in bands of yellow, tan, and white. The bands are formed by clouds. Saturn is a big ball of gas that spins rapidly, so the clouds are stretched into bands that completely encircle the planet.
If you look at those bands closely, though, Saturn takes on a more artistic appearance, like the works of a great Impressionist. Waves form at the boundaries between bands, spinning off whorls and eddies that are as big as continents.
Giant storms sometimes bubble up from deep within the planet. These blobs are quickly sheared apart by Saturn’s rotation. As they spread, they form waves and gyres that resemble cream swirling into a cup of hot coffee.
Saturn’s poles are among the most amazing views of all. The cloud bands around them form hexagons – the result of standing waves that constantly slosh around the planet. And there are vortexes at the poles themselves, with splashes of white clouds floating atop them – brilliant accents that crown Saturn’s beauty.
Again, look for the bright planet Saturn close to the Moon tonight, beginning before midnight.
Tomorrow: an arrow-wielding centaur transforms into a teapot.
Script by Damond Benningfield
[Launch Control: 25 seconds…]
When space shuttle Columbia headed for orbit 25 years ago tomorrow, it made history. It was the first mission commanded by a woman – Air Force pilot Eileen Collins. And it was carrying the heaviest payload ever lofted by a shuttle: Chandra X-Ray Observatory – the largest X-ray telescope ever flown.
[Launch Control: 5, 4, 3, we have a go for engine start, zero. We have booster ignition and liftoff of Columbia! Reaching new heights for women and X-ray astronomy.]
And Chandra is maintaining those heights – it’s still working.
The telescope studies some of the hottest and most energetic objects and events in the universe – exploding stars, outbursts from normal stars, gas around black holes, and much more. Such objects produce much of their energy in the form of X-rays. But Earth’s atmosphere blocks most X-rays, so the only way to study them is from space.
Chandra’s orbit carries it more than a third of the way to the Moon. That puts it outside most of Earth’s radiation belts, which can “fog” X-ray images.
X-rays go right through a normal telescope mirror. So Chandra uses a set of mirrors along the sides of the telescope tube. X-rays graze off those mirrors and come to a focus at the telescope’s instruments.
Chandra is still making history today – by keeping a sharp “eye” on the X-ray sky.
Script by Damond Benningfield
Pluto is at its best now. It’s lining up opposite the Sun. It rises around sunset and is in the sky all night. It’s brightest for the year as well. Don’t bother looking for it, though, unless you have a good-sized telescope.
Clyde Tombaugh was using a good-sized telescope when he discovered Pluto, in 1930. He’d been searching for a possible planet beyond Neptune for about a year, from Lowell Observatory in Arizona. When he found it, the little world was moving through Gemini.
Almost a century later, Pluto has advanced only a third of the way around the sky. That’s because Pluto is so remote that it takes 248 years to orbit the Sun – and to complete a single loop through the constellations. Today, it’s in the southwestern corner of Capricornus.
Pluto doesn’t move evenly across the sky. Its distance from the Sun varies from about 30 to almost 50 times Earth’s distance – a difference of 1.8 billion miles. It moves a lot faster when it’s closest to the Sun, so it crosses more of the starry background.
Pluto won’t complete its first orbit since its discovery until the year 2178 – when it will once again appear in Gemini.
For now, although you can’t see it, you can at least see its location. It’s between the handle of the “teapot” formed by the constellation Sagittarius, and the wide triangle that marks Capricornus. Tonight, that puts it not far to the upper right of the Moon.
Script by Damond Benningfield
Black holes are everywhere. There could be a hundred million black holes that are the remnants of dead stars in the Milky Way Galaxy alone. But because they’re completely dark, they’re hard to find. That applies even to the biggest member of the class yet discovered. It’s 33 times the mass of the Sun – more than half again the mass of the galaxy’s previous record holder.
The black hole is in a system known as BH3. It was discovered by the Gaia space telescope, which is mapping more than a billion stars in the galaxy. The system is almost 2,000 light-years from Earth.
The black hole revealed its presence only because it has a “normal” companion star. The companion is nearing the end of its life, so it’s becoming a giant – bigger and brighter than the Sun.
Gaia measured a wobble in the star’s motion. Astronomers analyzed the wobble, and decided that it was caused by the gravitational pull of a black hole.
The black hole probably formed when a supergiant star collapsed at the end of its life. That happened billions of years ago, when the galaxy was young – a conclusion supported by the age of the companion. The composition of the supergiant allowed it to form an especially heavy black hole – the biggest remnant black hole in the galaxy.
BH3 is to the left of the bright star Altair, the breast of the eagle, which is in the east at nightfall. But the system is much too faint to see without a big telescope.
Script by Damond Benningfield
The human eye is tuned to a narrow band of wavelengths: visible light. But the electromagnetic spectrum extends far beyond our ability to see – from radio waves to gamma rays. Each slice of the spectrum tells us different things about the universe.
Consider X-rays. We’re most familiar with them in medical settings. But many astronomical objects produce their own X-rays, allowing astronomers to diagnose their details.
The list includes many types of stars. Many stars have hot, X-ray-producing outer atmospheres. Stars also generate big eruptions, known as flares. Studying these events tells us more about how stars age, and how they interact with the universe around them.
X-rays are especially common in some of the most violent objects and events in the universe. Exploding stars heat their environment to millions of degrees – producing X-rays galore. And disks of hot gas around black holes are also X-ray sources. The X-rays can reveal the amount of gas, the size of the disk, and how fast the gas is moving.
There’s one problem, though: Earth’s atmosphere absorbs X-rays. So astronomers loft their telescopes as high as possible. They’ve used rockets, balloons, and a rocket-balloon combination called a rockoon. But most of what we know about the X-ray sky came from space telescopes. The largest and most powerful X-ray telescope to date was launched 25 years ago next week, and we’ll talk about that on Monday.
Script by Damond Benningfield
If you ever visit the planet Mercury, take along your old eclipse glasses. They’re not for looking at the Sun – you might need something even darker for that. Instead, you might want them just to see your way across the planet itself. Mercury is so close to the Sun that sunlight is more than 10 times more intense than on Earth.
Mercury is the closest planet to the Sun – an average of about 40 percent of Earth’s distance. But Mercury’s orbit is the most lopsided of any of the Sun’s major planets. So when Mercury is closest to the Sun, sunlight is almost two-and-a-half times as intense as when the planet is farthest.
All of that solar energy makes Mercury the second-hottest planet – only Venus is hotter. At the equator, temperatures hit about 800 degrees Fahrenheit.
But that doesn’t mean you couldn’t beat the heat. Mercury doesn’t have an atmosphere to circulate heat around the planet. So nighttime temperatures drop to almost 300 below zero. And the bottoms of some craters at the poles never see the Sun at all. They stay cold enough to preserve big deposits of ice – perfect places to beat the heat on a scorching planet.
Mercury is just peeking into view in the evening twilight. It looks like a fairly bright star, quite low in the west as night falls. The view is better from southern locations. So while you might not see it at all from Minneapolis, you shouldn’t have any trouble from San Antonio or Miami.
Script by Damond Benningfield
You don’t have to be an astronaut to see the far side of the Moon – at least some of it. A little bit of that hemisphere wobbles into view every month – an effect known as “libration.” So we can actually see 59 percent of the lunar surface.
The Moon is “locked” in such a way that the same hemisphere always faces Earth. That means we see the same features all the time – the same dark volcanic plains, and the same lighter-colored jumbles of mountains, valleys, and craters. Almost.
As the Moon orbits Earth, we get some peeks at the other hemisphere – the far side. The Moon is tilted a bit on its axis, for example. So as it orbits Earth, it appears to “nod” up and down a bit – just as Earth appears to nod as seen from the Sun. That allows us to see just beyond the north and south poles.
Also, the Moon’s distance from Earth isn’t constant – it varies by almost 30,000 miles. As a result, the Moon’s orbital speed goes up and down. But the rate at which the Moon spins on its axis remains constant. That allows us to see a little bit around the eastern and western edges – glimpses of a little bit of the lunar farside.
As darkness falls this evening, we’ll see a little bit beyond the north pole. We’ll also see a little bit beyond the western limb – or would if that part of the lunar disk weren’t in darkness. As a bonus, the Moon has a close companion: Antares, the bright heart of the scorpion.
Script by Damond Benningfield
The stars that represent the head of the scorpion are impressive families within an even more impressive clan. Each of them looks like a bright point of light. But each one consists of two or more stars, all of which are much bigger, heavier, and brighter than the Sun.
The stars align near the Moon this evening. From the top, the stars are known as Pi, Delta, and Beta Scorpii.
Pi Scorpii consists of three stars. The most massive of the trio is destined to blast itself to bits as a supernova sometime in the next few million years. And another member appears to be just massive enough to become a supernova as well.
Delta is a binary. One of its stars is also a future supernova, while the other is along the dividing line – it might be heavy enough to become a supernova, but it might not.
Beta is the brightest of the three stars. It’s also the most complicated. It consists of six stars that orbit each other in a complex gravitational dance. At least two of the stars will become supernovas, and perhaps as many as four.
All three systems were born from the same giant complex of gas and dust. And all of their stars are quite young – no more than about 15 million years old, compared to four and a half billion years for the Sun.
Another sibling is Antares, the bright orange star that marks the scorpion’s heart. The Moon will snuggle up to it tomorrow night, and we’ll have more about that tomorrow.
Script by Damond Benningfield
Scorpius is immersed in the Milky Way – the hazy band of light that outlines the disk of the Milky Way Galaxy. Because of that, the constellation is home to a dense variety of star clusters. Some of them are young, so they hold some especially bright stars.
Two examples are Messier 6 and 7.
M7 is the brighter of the two. Under dark skies, it’s fairly easy to see with the unaided eye. It’s about a thousand light-years away, and it contains hundreds of stars.
M7 appears to be about 200 million years old. At that age, all of its most-massive stars have long since blasted themselves to bits. That’s because heavy stars use up their nuclear fuel in a hurry. But the cluster still contains some stars that are a good bit bigger, brighter, and heavier than the Sun.
M6 may be just half as old as M7, so some of its stars are more impressive than any in M7. But astronomers have cataloged fewer stars there. And the cluster is hundreds of light-years farther than M7, so it’s harder to see – a faint family of stars in the Milky Way.
Look for the clusters quite low in the southern sky at nightfall. They’re to the upper left of the stars that form the “stinger” of the scorpion. M7 is about half way between the stinger and the “spout” of the teapot formed by the next-door constellation Sagittarius. Fainter M6 is a little higher in the sky. Both clusters are good targets for binoculars.
Script by Damond Benningfield
A few star patterns are easy to pick out. There’s Orion, with his prominent “belt.” There’s the Big Dipper. And on summer evenings, there’s Scorpius. It really does look like a scorpion skittering along the horizon.
Some of the stars that outline the scorpion are related – they were born from the same giant complex of gas and dust. That includes Antares, the scorpion’s bright orange heart.
Antares and the other family members we can see with our eyes alone are all supergiants – many times the size and mass of the Sun. And all of them are quite young – no more than 10 million to 15 million years old. None of these showoffs will stick around much longer, though. Such heavy stars “burn” through their nuclear fuel in a hurry. At the end of their short lives, they explode – briefly outshining the combined light of most of the galaxy’s other stars.
But the supergiants aren’t the only stars in this impressive family. Thousands of smaller and fainter stars have been born in the same complex. And thousands more are taking shape today – less-flashy stars that will outlive their brilliant siblings.
Scorpius is in the south at nightfall, quite low above the horizon. It has a curving body with a prominent “stinger” at the end, like a big letter “J.” Some cultures have seen it as a fishhook. Either way, it’s one of the easiest star patterns to pick out in all the night sky.
More about Scorpius tomorrow.
Script by Damond Benningfield
The Moon gets especially cozy with the star Spica this evening. From much of the United States, in fact, the Moon will pass in front of the bright star, blocking it from view for a while. Astronomers will keep an eye on the event – called an occultation – to learn more about Spica.
In earlier days, occultations also helped scientists map the Moon. The way a star disappeared and reappeared could reveal the contours of lunar mountains, valleys, and craters. We still see those features during occultations, but they’ve been well mapped.
Scientists have been making maps of the Moon for centuries. Perhaps the earliest known map – a truly accurate chart of lunar features – was created by William Gilbert, a British scientist and a physician to Queen Elizabeth I. He drew it no later than 1603, before the invention of the telescope, using his eyes alone. But it wasn’t published until 1651.
By then, Polish astronomer Johannes Hevelius had published a whole atlas of the Moon, made with a telescope. He named many of the lunar features. Eventually, though, the names were superseded by those created just a few years later by Giovanni Riccioli, a scientist and Jesuit priest. And most of his names are still in use today.
Many more names have been added in recent decades, thanks to the detailed pictures taken by orbiting spacecraft. All of those names are found on modern maps of the Moon.
Script by Damond Benningfield
It would take a couple of hours to fly from Chesapeake Bay, on the coast of Virginia, to the forests and swamps of eastern Texas. But about 35 million years ago, some brownish-green bits of glass made the trip in just minutes – the result of a massive collision between Earth and a space rock.
The rock was an asteroid or comet, and was perhaps two or three miles in diameter. It slammed into the coastline at tens of thousands of miles per hour. The impact gouged a crater about 50 miles across and a mile deep, which later became Chesapeake Bay.
The collision vaporized the space rock and some of the ground it hit. It also blasted millions of tons of water, mud, and granite high into the sky.
The heat of the impact melted sand and some of the other debris. Molten droplets blasted through the air at thousands of miles per hour. Many of them were sculpted into aerodynamic shapes, like teardrops or spheres. As they cooled, they fell to Earth as pieces of glass known as tektites.
A major field of them has been found in Georgia. Another is in Texas. Its tektites are known as Bediasites. They’re named for a small town, which took the name from a native tribe that inhabited the region long ago.
The first Bediasites were discovered in 1936. The largest is nicknamed the “Star of Sabine” for the location where it was found. It weighs about seven ounces – a large chunk of colored glass that crossed half a continent in a hurry.
Script by Damond Benningfield
A dwarf planet far from the Sun may spend most of its time outside the Sun’s influence. In fact, it might have come from interstellar space – from another star.
Sedna takes more than 11,000 years to orbit the Sun. It’s passing through the Kuiper Belt – a wide “doughnut” far beyond the orbit of Neptune, the Sun’s most distant major planet. Right now, Sedna’s almost eight billion miles from the Sun – about as close as it ever gets. At its most distant, it’s more than 10 times farther. That places it far beyond the Kuiper Belt – and well outside the “bubble” produced by the Sun’s magnetic field.
Scientists have speculated that Sedna started in the Oort Cloud – a big “shell” of rocky, icy bodies that surrounds the Sun. It could have been pushed into its elongated orbit by the gravity of a passing star. Or it could have been a member of another star system that was pulled away by the Sun.
There’s one other oddity about Sedna’s orbit: It seems to be influenced by the gravity of a much larger but unseen body far from the Sun – a possible “Planet Nine.”
Because Sedna’s so far away, we don’t know a lot about it. It’s probably about 600 miles in diameter. And it’s quite red – an indication that radiation has been zapping its surface for a long, long time. No one has found a moon yet, so it’s hard to measure Sedna’s mass. So we still have a lot to learn about this remote little world far, far from the Sun.
Script by Damond Benningfield
Pluto is the largest known member of the Kuiper Belt – a wide zone beyond the orbit of Neptune, the Sun’s most remote major planet. But Pluto isn’t the most massive member of the belt. That distinction goes to Eris – a fellow dwarf planet that may be a lot like Pluto.
Eris was discovered almost 20 years ago. It wasn’t noticed earlier because it’s a long way from the Sun – almost three times Pluto’s distance. At that range, it looks quite faint. And it creeps along against the background of stars, so it took a while to realize that it’s a member of the solar system.
Eris is a tiny bit smaller than Pluto. But it’s a good bit more massive. That means it’s denser than Pluto – it has a higher ratio of rock to ice. But like Pluto, it’s probably still geologically active.
One indication of that is that the surface of Eris is almost pure white – it reflects almost all of the sunlight that strikes it. That suggests that fresh ice is erupting from its interior, repaving the surface.
Another indication is the chemistry of methane ice at the surface. Observations by Webb Space Telescope showed that the methane probably formed from chemical reactions between water and carbon inside the little world. Such material must be constantly renewed – oozing to the surface through cracks or holes in the icy surface of Eris – the heaviest of the Sun’s dwarf planets.
We’ll talk about another dwarf planet tomorrow.
Script by Damond Benningfield
The planets of the solar system come in three varieties: the rocky planets, like Earth; the giant planets, like Jupiter; and dwarf planets, like Pluto. The first two groups are well known. Except for Pluto, though, the third group is pretty much anonymous to everyone except scientists who study them.
Astronomers created the dwarf-planet category in 2006, after they began finding bodies similar to Pluto in the outer system. A dwarf planet must orbit the Sun and not some other object, and it must be mostly round. Today, the count varies. But most lists include at least eight members. And some say that scores of known objects could fit the category, with hundreds more awaiting discovery.
One definite dwarf planet is Ceres, in the asteroid belt, between the orbits of Mars and Jupiter. All the others are beyond Neptune, the most remote major planet. Most of them are in the Kuiper Belt – a doughnut that extends billions of miles beyond Neptune.
Pluto is the largest dwarf planet, and the closest to the Sun. The second largest is Eris. It’s actually a little heavier than Pluto, which means it’s also a little denser. We’ll have more about Eris tomorrow.
Most of these distant little worlds have icy surfaces. But a few could have active interiors, with possible oceans of liquid water. That means at least some of them are possible habitats for life – in the deep freeze of the outer solar system.
Script by Damond Benningfield
If astronomers at the star Regulus could pick up radio broadcasts from Earth, right about now they’d be hearing something like this: [1945 audio clips]
They’d just now be hearing about the final days of World War II because Regulus is a bit more than 79 light-years away. That means it takes more than 79 years for light – including radio waves – to travel from Earth to Regulus, or from Regulus to Earth. So the light we see from Regulus tonight actually left the star in 1945. And if anything dramatic were to happen to the star tonight, we wouldn’t know about it until 2103.
79 light-years is a huge distance. Light travels at 670 million miles per hour. That means Regulus is almost 500 trillion miles away – a five followed by 14 zeroes.
Such vast distances make many people skeptical that we could ever have a chat with another civilization. It might take generations from the time one side said “hello” until the other could respond. So some day we might hear a broadcast from another civilization. But we’ll probably never become best buds.
Look for Regulus to the upper left of the Moon in the evening twilight – a close neighbor that’s not close enough for a neighborly chat.
Script by Damond Benningfield
About 10,000 years ago, a massive star in Cygnus, the swan, blew itself to bits. For a few days or weeks, it blazed as the brightest object in the night sky other than the Moon – bright enough to see even during the day. Today, its glowing remains are still visible – a colorful bubble that’s more than a hundred light-years across and growing.
The bubble is known as the Cygnus Loop. It’s a supernova remnant – the debris from a star that was about 20 times the mass of the Sun. After a short but brilliant life, the star could no longer produce nuclear energy in its core. The core collapsed, and the star’s outer layers exploded at a few percent of the speed of light.
As the bubble expands, it rams into surrounding clouds of gas and dust. That causes parts of the bubble to glow, forming the Veil Nebula and some other structures. Images reveal ribbons of gas and dust that intertwine like the strands of a rope. They shine in shades of red, blue, green, and other colors – the result of the elements they contain. Other parts of the Loop shine in wavelengths that are invisible to the human eye.
The Cygnus Loop is in the east-northeast at nightfall, to the lower right of Deneb, the bright star at the swan’s tail. The loop spans about six times the width of the full Moon. Small telescopes equipped with the right filters reveal some of the glowing filaments – the fading remnants of a stellar spectacle.
Script by Damond Benningfield
Three tiny constellations are stacked up in the eastern evening sky this month: the arrow, the dolphin, and the little horse. There’s not a single bright star among them. But under moderately dark skies, at least one of them is pretty easy to make out.
The arrow is at the top of the stack. It’s the third-smallest of the 88 modern constellations. In ancient times, it represented a weapon used by Hercules, but there were different takes on his target. All of its stars are faint, but under especially dark skies, it does look like an arrow, aiming toward the left. It’s between two bright stars: Altair, to its lower right, and Deneb, to the upper left.
The most prominent of the three figures is the dolphin, which is below the arrow. Its five brightest stars outline the dolphin’s form. It, too, has more than one myth. One of them said the dolphin rescued a rich poet and musician. The man had jumped into the sea after he was threatened by the crew of the ship in which he was sailing.
Finally, there’s the little horse. It’s the second-smallest constellation, and it’s quite faint. And it’s not even a complete horse – it’s depicted only as a horse’s head. One of its Greek stories said it was the brother or son of the winged horse Pegasus, which rises below it.
If your skies are nice and dark, look for these tiny constellations beginning at nightfall, and rolling across the south during the night.
Script by Damond Benningfield
The Sun and the planet Jupiter are the heaviest objects in the solar system. But there’s a huge gap in their masses – the Sun is more than a thousand times heavier.
There’s a class of objects between those masses. Known as brown dwarfs, they’re much heavier than Jupiter, but no more than seven or eight percent of the Sun’s mass.
A brown dwarf probably forms in the same way as a star – from the collapse of a cloud of gas and dust. The heat of that collapse makes the brown dwarf shine. But a brown dwarf isn’t massive enough to “fuse” hydrogen atoms in its core to make helium – the power source of most true stars. It may briefly fuse a heavy form of hydrogen, but that doesn’t produce nearly as much energy. So brown dwarfs are also known as “failed stars.”
The surface of a brown dwarf can be so cool that clouds can form in its upper layers, making it look like a giant planet, such as Jupiter. And despite the name, brown dwarfs aren’t really brown. Their color can range from dull orange or red to dark purple to black – a result of the surface temperature and chemistry.
The closest brown dwarfs form a binary known as Luhman 16. The system is six and a half light-years away – closer than only two star systems. Even so, it took a special space telescope to discover the pair – faint “missing links” between true stars and giant planets.
Script by Damond Benningfield
It may sound strange to hear during the heat of the summer, but Earth is farthest from the Sun for the entire year right now. Our planet is receiving almost seven percent less energy from the Sun than it did when it was closest to the Sun, in January.
The average distance to the Sun is 93 million miles. But the distance varies by about one and a half million miles in either direction – a result of the eccentricity of Earth’s orbit. It defines how lopsided the orbit is. And it varies over cycles of hundreds of thousands of years.
The change is caused by the gravitational pull of the other planets. The biggest impact comes from Venus and Jupiter. Venus passes closer to us than any other planet. And Jupiter is the solar system’s heaviest planet. So even though it’s a long way off, it has a big influence on Earth’s orbit.
Today, the eccentricity is less than two percent, so Earth’s orbit is almost circular. And it’s getting even more circular. When the eccentricity is lowest, the distance to the Sun will vary by only about 300,000 miles.
After that, the orbit will get much more eccentric. It’ll peak at almost six percent. That may not sound like a lot, but it’s enough to change the amount of sunlight Earth receives over the course of a year by 23 percent. That difference will have a major impact on Earth’s climate – thanks to the influence of the other worlds of the solar system.
Script by Damond Benningfield
Betelgeuse grew dramatically fainter a couple of years ago. The supergiant star blasted out a giant blob of gas, which cooled to form a dust cloud that blocked part of the star from view. And a similar star might recently have gone through the same process.
RW Cephei is at least 900 times the diameter of the Sun, making it one of the larger stars in the galaxy. It’s also hundreds of thousands of times brighter than the Sun. In late 2022, though, it dropped to a third of its usual brightness. By last summer, it was recovering.
Astronomers analyzed some especially sharp images of the star. The pictures showed that it was blobby, with bright and dark regions many times larger than the Sun.
The astronomers later found that RW Ceph had grown brighter than usual in 2019. It may have blown out a huge blob of hot gas not long after that. The gas cooled and condensed to form a cloud of dust grains. The cloud moved in front of the star, causing it to fade. As the cloud dispersed, RW Ceph returned to its usual brilliance.
The hypergiant star is near the end of its life. It’s expected to explode as a supernova sometime in the next million years or so – just like Betelgeuse.
RW Cephei is low in the northeast at nightfall. It’s about halfway between Deneb, the star at the tail of the swan, and W-shaped Cassiopeia. Even at its best, though, you need binoculars or a telescope to see it.
Script by Damond Benningfield
The four big moons of Jupiter probably are all about four and a half billion years old. But two of them look much younger. That’s because their surfaces are constantly repaved – one by fire, the other by ice.
The fire moon is Io. It’s the most volcanically active body in the solar system, with more than 400 volcanoes on its surface. Some of them release gas or lava, while others produce big explosions. That activity covers up any impact craters – the scars of collisions with big space rocks. Scientists have reported only one possible crater on Io – a good indication that the surface is young.
The ice moon is Europa. It has more craters than Io, but not a lot. That’s because it appears to have an ocean of liquid water below its icy crust. Water may ooze from the ocean, coating parts of the crust.
Some impacts by big space rocks may punch through the crust, allowing more water to reach the surface. And a recent study by scientists at the University of Texas found that an impact doesn’t have to go all the way through the ice. If it rams halfway through, it can melt enough ice for the warm water to melt the rest of the way to the ocean. That may allow some of the ocean water to reach the surface – helping Europa keep its “youthful” appearance.
Look for Jupiter near our own moon at dawn tomorrow. The planet looks like a brilliant star. Through binoculars, its big moons look like tiny stars arrayed near the planet.
Script by Damond Benningfield
Mars and Jupiter are siblings. They were born at the same time, from the same cloud of material that encircled the embryonic Sun. Yet there’s absolutely no family resemblance – they could hardly be more different.
Both planets appear near the Moon at dawn tomorrow. Mars looks like a bright orange star to the upper right of the Moon. Jupiter is even brighter, and crouches below the Moon, low above the horizon.
Mars is small – about half the diameter of Earth. It’s made of rock and metal. Jupiter, on the other hand, is the largest planet in the solar system – a giant ball of gas that’s 20 times wider than Mars, and about 3,000 times as massive. In fact, Jupiter is more massive than all the other planets and moons in the solar system combined.
Mars and Jupiter are the fourth and fifth planets out from the Sun, so you might expect them to be more alike. But Jupiter might have formed farther from the Sun than it is now. At that distance, conditions would have been quite cold. There would have been a lot of ice and gas for Jupiter to sweep up, allowing it to grow bigger and bigger.
Mars was born closer to the Sun. Solar heat and radiation cleared out most of the ice and gas in its region. That left mainly bits of rock and metal – the stuff that came together to form the planet Mars – a world quite different from its giant sibling.
We’ll have more about the Moon and Jupiter tomorrow.
Script by Damond Benningfield
The moons of Mars aren’t much more than big boulders that look a bit like potatoes. Phobos is about 17 miles long; Deimos, only about nine miles. But they’ve been the subject of a big scientific debate for decades — a debate about their origins.
One possibility says they’re asteroids that were captured by Mars long ago. Both bodies look like asteroids. And some of the minerals on one of them are the same as those found in some meteorites that probably came from asteroids.
The other possibility says they formed after a giant impact. A large body could have rammed into Mars early in its history. That blasted out material from both Mars and the impactor, forming a ring of debris around Mars. Phobos and Deimos formed from that debris. That idea seems to explain the moons’ orbits, but not necessarily their composition. But a recent study may have found a way to make it work.
It says that the impacting body was made mainly of frozen water. Such a body would have blasted out more debris than one made mainly of rock. And the vaporized water would have kept the debris cool enough to allow the formation of some of the minerals on the moons. Ice-rich bodies could have been fairly common in the early solar system — providing a way to create the moons of Mars.
Bright orange Mars is close to our own moon the next two mornings. It’s directly below the Moon at dawn tomorrow, and to the upper right of the Moon on Tuesday. More tomorrow.
Script by Damond Benningfield
A small, faint “shield” of stars scoots across the southern sky on early summer nights. It represents the coat of arms on the shield of John Sobieski, a 17th-century king of Poland and one of the country’s great national heroes.
The shield is the constellation Scutum. Johannes Hevelius first drew it around 1687, using a few stars from a fairly empty region of the sky. He originally named it Scutum Sobiescianum — the shield of Sobieski. But in more recent times, the last part of the name has been dropped.
Sobieski became king of Poland in 1674. He built alliances with several European neighbors, and fought the Ottoman Empire when it tried to expand westward. In 1683, he earned fame all across Europe by defending Vienna against the Ottoman army.
To honor his native country, Hevelius included the new constellation in a beautiful star atlas, which was published in 1690. He depicted several faint stars as the cross on Sobieski’s shield. The shield has kept its place in the stars ever since then.
Unfortunately, the stellar shield isn’t all that much to look at. You need fairly dark skies to see any of its stars. Right now, it’s low in the southeast as night falls. It’s to the upper left of the teapot-shaped constellation Sagittarius. Scutum wheels low across the south during the night, and is in the southwest at dawn.
Script by Damond Benningfield
Hurricanes and other big storms can cause widespread damage that can take days or weeks to clean up. So can big space weather storms. They can knock out satellites, disrupt radio transmissions, and cause power blackouts. Especially big storms have the potential to knock out power grids for weeks or months. So scientists and power operators are looking for ways to minimize the damage.
Space weather is powered by storms on the Sun. Big explosions send particles and energy racing out into the solar system. Earth’s magnetic field funnels some of the particles toward the surface. They can create powerful currents in electrical equipment and even in the ground. That can trigger blackouts. At their worst, they might fry transformers and other gear, completely wrecking power grids.
Scientists in New Zealand recently worked with the national power operator to simulate ways to minimize the impact of a major storm. Their work showed that disconnecting a limited number of key high-power transmission lines reduced the risk of a system-wide failure. It also showed that installing a sort of surge protector on some transformers could provide similar protection.
The Sun is nearing the peak of its current activity cycle. Big outbursts in March, in fact, triggered the highest warning levels in more than six years. Similar warnings could be common in the coming months — as the Sun stirs up powerful space weather.
Script by Damond Benningfield
A dark ribbon of gas and dust may be about to light up like a sequence of camera flashes. That’s because it could begin giving birth to new stars, with each star triggering the birth of more stars.
The ribbon is called the Nessie Nebula — named for its resemblance to the Loch Ness monster. It’s the longest ribbon of its type yet seen in the Milky Way — about 300 light-years long, but only three light-years across. It’s chilled to about 20 degrees above absolute zero. And for every light-year of its length, there’s enough gas and dust to make 200 stars as massive as the Sun.
While Nessie itself is dark, it has a bright “head” — a bubble of hot gas. The bubble contains young, heavy stars. The stars are blowing away the gas around them, forming the bubble. It’s ramming into Nessie’s dark “body.” And that appears to be triggering the birth of another heavy star.
That could set off the chain reaction. As a big star is born, it produces powerful winds. They push material away from the star, forming a bubble that squeezes the surrounding gas and dust. If this material is squeezed tightly enough, it collapses to form a new star. The newborn, in turn, produces its own bubble, triggering the birth of more stars, and so on.
Because Nessie is so long, it’ll take millions of years for that process to play out. Eventually, though, the dark nebula may be replaced by the glow of thousands of stars.
Script by Damond Benningfield
After the New Horizons spacecraft flew past Pluto, in 2015, it still had some gas in the tank and some tread on the tires. Mission scientists wanted to take advantage of that by flying past another object in the outer solar system. But they didn’t know where to send it — there was no roadmap to other destinations.
They solved that problem 10 years ago today. Using Hubble Space Telescope, they discovered a new body about four billion miles from the Sun. Eventually, it was named Arrokoth — a Powhatan name for “sky” or “cloud.”
New Horizons flew just 2200 miles from Arrokoth in early 2019. It’s the most distant object ever seen from close range.
Arrokoth is about 22 miles long. It consists of two “lobes” — one a few miles wider than the other. That makes the object look like a smushed snowman, or a rubber duck without a bill. The two lobes probably began as separate objects, but they gently mashed together.
A recent study found that the bigger lobe probably was formed from several smaller bodies — chunks of ice and rock a few miles across that all mashed together.
New Horizons found water ice, methanol, and organic compounds on the surface of Arrokoth. Radiation from the Sun and beyond has zapped the organic molecules, turning them red. Scientists are still studying the observations to learn more about Arrokoth — a distant encounter on a long road trip.
Script by Damond Benningfield
Just like magic, big “islands” appear to come and go on the lakes and seas of Titan, the largest moon of Saturn. They first showed up in radar images snapped 10 years ago by the Cassini spacecraft. And planetary scientists have been trying to explain them ever since.
Titan is bigger than the planet Mercury. It has a cold, thick atmosphere. Hydrocarbons at the top of the atmosphere create an orange haze — like the smog that blankets many cities. Methane and ethane form clouds. They also fill the lakes and seas.
In most of Cassini’s images, these bodies of liquid looked dark and calm — any waves would be no more than a fraction of an inch high. But occasionally, a bright patch would appear — like an island suddenly rising from the depths.
There are several possible explanations: big waves, patches of nitrogen bubbles, and others. And a study this year suggested sheets of ice. In this scenario, particles would drop from the haze layer, forming ice grains along the way. The grains could collect in sheets along the shore. The ice would be porous, like a sponge or a honeycomb. A sheet might break away and float into a lake or sea. Eventually, though, the spaces would fill up, the ice would sink, and the island would vanish — just like magic.
Look for Saturn near our own moon the next few mornings. It’ll stand well to the left of the Moon at dawn tomorrow, but much closer to the Moon on Thursday.
Script by Damond Benningfield
Almost all of the planetary action is in the morning sky now. Mercury is trying to climb into view in the evening sky, but it’s low and tough to see. It’ll be in slightly better view in a few days.
Three planets are in the morning sky. Two of them climb into view a good while before dawn, so there’s plenty of time to look for them. The third is just coming into view after passing behind the Sun. It’s quite bright, though, so it’s pretty easy to pick out.
As twilight begins to paint the morning, look half-way up the southeastern sky for Saturn, which looks like a bright golden star. Tomorrow, it’s far to the upper left of the Moon. But the Moon will soon catch up to it, and we’ll have more about that tomorrow.
Saturn is the second-largest planet in the solar system. But it’s best known for its beautiful rings. They’re made mainly of bits of ice, so they reflect a lot of sunlight. That enhances the planet’s brightness.
Next look for Mars, which is due east. It’s only about half as high as Saturn is, but it shines just as brightly. The dust that coats much of its surface gives Mars an orange tint, so it’s hard to miss.
Finally, as twilight brightens, look well to the lower left of Mars for Jupiter, the Sun’s largest planet. Although it’s low, it’s quite bright — only the Moon outshines it in the current night sky. So it’s easy to see deep into the waxing twilight — the dawn of a new day.
Script by Damond Benningfield
Altair is the brightest star in the constellation known as the eagle, and one of the 12 brightest stars in the night sky. But a fainter star that appears just above it as night falls is actually a whole lot brighter. It only looks fainter because it’s a whole lot farther away.
Tarazed looks only about one-sixth as bright as Altair. But it’s 35 times farther than Altair. When you take that into account, Tarazed shines a couple of hundred times brighter.
Over the past few years, astronomers have refined the distance to the star using observations from Gaia, a European space telescope. It’s measuring the distances to more than a billion stars, and compiling detailed profiles of many of them.
Gaia determines a star’s distance by measuring its parallax. It observes a star at six-month intervals, when Gaia is on opposite sides of the Sun. The star appears to move back and forth a tiny bit against the background of more-distant objects. The angle of that shift reveals the star’s distance.
Gaia found that Tarazed is a couple of hundred light-years farther than astronomers had thought. That means it’s also bigger and brighter than thought — and much more impressive than nearby Altair.
Watch Tarazed as it leads Altair across the sky on summer nights. The stars are low in the east as darkness falls, due south in the wee hours of the morning, and high in the southwest at dawn.
Tomorrow: planets in the dawn sky.
Script by Damond Benningfield
A young eagle soars across the sky on summer nights. Right now, it’s low in the east at nightfall, due south in the wee hours of the morning, and high in the southwest at dawn. And it’s easy to spot — it’s the 12th-brightest star in the night sky.
Altair represents the breast of the constellation known as the eagle. The name “Altair,” in fact, means “the flying eagle.”
According to current understanding, it’s a young eagle — barely more than an eaglet. It’s about a hundred million years old, compared to four and a half billion years for the Sun. And it’s just entering stellar adulthood — what’s known as the “main sequence.” That means it’s fully formed, and it generates energy through nuclear fusion in its core — it “fuses” together hydrogen atoms to make helium.
One of the hallmarks of young stars is that they spin in a hurry — a result of the collapse of the cloud of gas and dust that gave them birth. And Altair is no exception. It turns on its axis once every eight hours, compared to almost a month for the Sun. That’s about 75 percent of the speed needed to make Altair fly apart.
The whirligig action also flattens the star, so it’s almost 25 percent fatter through the equator than through the poles — an effect clearly seen in images of Altair — a young, bright eagle flying through summer nights.
Altair has a close attendant, and we’ll talk about that star tomorrow.
Script by Damond Benningfield
There’s an astronomical coincidence today: It’s the first full day of summer in the northern hemisphere, and there’s a full Moon. The exact moments of the full Moon and the summer solstice are a bit more than one day apart — a coincidence that happens, on average, once every couple of decades.
At full Moon, it’s daylight across the entire lunar hemisphere that faces our way. But not every location sees the Sun. Some craters near the lunar poles are so deep that sunlight never reaches their bottoms.
That doesn’t mean the crater floors are completely dark. The lighting may be comparable to a family den or even an office building.
Scientists have measured the light levels with a NASA instrument called ShadowCam. It’s on a Korean spacecraft that’s been orbiting the Moon for the past year and a half. The instrument can see into regions that are too dark for other spacecraft.
There’s no atmosphere on the Moon to scatter sunlight. But sunlight that hits the rims of the craters or nearby mountains is reflected into a crater’s depths. Scientists recreated those lighting conditions in an office. And they found that there was plenty of light for working.
Craters near the south pole are prime landing sites for future missions because they may contain a lot of frozen water. Astronauts probably won’t need headlights to find their way around those craters — reflected sunlight should provide all the light they need.
Script by Damond Benningfield
For many countries in Europe, today is Midsummer Day. It’s marked with bonfires and other celebrations. It marks the middle of summer, which began back in May.
Astronomically, though, today marks the start of summer in the northern hemisphere. It’s the summer solstice — the longest day of the year. It marks a turning point for the Sun, which will begin to move southward after today.
Regardless of whether it was considered the start of summer or its middle, the solstice had great significance for cultures around the world. They held festivals and religious ceremonies to celebrate the light.
Many cultures used natural alignments to track the Sun’s motions along the horizon, allowing them to pinpoint the date. They also made their own alignments.
One of the most famous examples is Stonehenge in England. But there are plenty of examples in the Americas as well.
In the United States, many are still found in the southwest, in the remnants of ancient pueblo sites. Many of the solstice markers are spirals carved or painted on rock surfaces. The rising Sun passes through cracks or notches in the nearby rocks, creating daggers of light across the spirals.
Other markers were built into houses or ceremonial structures. Narrow windows, for example, might allow the sunlight to shine onto symbols on the opposite wall — symbols dedicated to the rising Sun on the summer solstice.
We’ll have more about the solstice tomorrow.
Script by Damond Benningfield
You might think that astronomers would know just about everything there is to know about the brighter stars in the night sky. That’s not the case, though. In fact, some of those stars can be especially vexing.
An example is Antares, the orange supergiant that marks the heart of Scorpius, the scorpion. The star huddles quite close to the Moon at nightfall, with the gap growing smaller as the night goes on.
Antares is the 15th-brightest star in the night sky. And astronomers do know quite a bit about it. It’s roughly a dozen times as massive as the Sun, perhaps a thousand times wider, and tens of thousands of times brighter.
The star’s brightness isn’t constant, though. It appears to vary by a few percent. But just how much it varies, and how often, are poorly understood. Estimates for the period of the changes range from about three years to six years. The star may be pulsing in and out like a beating heart. Or bubbles of hot gas bigger than the Sun may occasionally rise to the surface, then sink back into Antares, changing the star’s brightness.
The American Association of Variable Star Observers has been keeping its eyes on Antares since 1945. And it’s been using electronic instruments in that effort since 1981. Even with those decades of observations, though, astronomers still don’t have a good understanding of how and why this massive star changes brightness.
Tomorrow: summertime.
Script by Damond Benningfield
Building the Albert Dock in Liverpool gave a man a powerful thirst. Workers drank up to a dozen pints of beer a day — and that was during the work day, with beer provided by the company. And while the workers drank, beer baron William Lassell got rich.
Lassell used some of that wealth to study the stars. He designed and built one of the world’s largest telescopes, and used it to make many important discoveries.
Lassell was born 225 years ago today. He made his first telescope by age 21. In the 1830s, he built an estate in Liverpool and called it “Starfield.”
At the time, there were few professional astronomers anywhere. Much of the leading research was done by wealthy amateurs like Lassell. In the 1840s, he designed a steam-powered machine to grind the mirror for a 24-inch telescope — one of the largest in the world. The telescope was a trendsetter, because it could track objects across the entire sky.
Using this new instrument, Lassell discovered Triton, the largest moon of Neptune, plus two moons of Uranus and one of Saturn. Later, he moved the telescope to the Mediterranean to escape Liverpool’s rainy, polluted skies. And later still, he built an even bigger telescope.
William Lassell died in 1880. But his contributions remind us of an important era for astronomy — an era made possible by the thirst for knowledge — not to mention the thirst for beer.
Script by Damond Benningfield
Modern astronomy is a job for professionals. Amateurs discover comets and make many other contributions. But most of the cutting-edge research is done by professional scientists using expensive telescopes and other equipment.
In the not-so-distant past, though, many major discoveries were made by “gentleman astronomers” — rich men who built their own telescopes and shared a passion for the stars.
That was especially true in Britain. There wasn’t much public money for telescopes, and only a handful of men made their living as full-time astronomers.
In fact, the Royal Astronomical Society was dominated by amateurs — doctors, lawyers, clergymen, and industrialists who had the time, money, and desire to study the heavens. They built entire observatories — sometimes in England, sometimes in parts of the globe with better climates for skywatching.
In 1845, William Parsons, the Earle of Rosse, built the largest telescope in the world at his estate in Ireland. Its mirror was six feet across, and the 60-foot tube was maneuvered by ropes, pulleys, and cranes. With this behemoth, Parsons drew beautiful sketches of galaxies, and suggested they were “cities of stars” beyond the Milky Way.
And in 1846, beer baron William Lassell discovered Triton, the largest moon of the planet Neptune, with a telescope of his own design. We’ll have more about this “gentleman astronomer” tomorrow.
Script by Damond Benningfield
A pair of cat’s eyes glows just above the north-northwestern horizon as darkness falls. The glowing eyes drop from sight in a hurry. And they’ll drop even lower during the coming nights, before disappearing entirely in the evening twilight.
The “eyes” are the stars Pollux and Castor. They mark the heads of the constellation Gemini. The stars are described as “twins,” but that’s mainly because they’re so close together. Pollux is actually twice as bright as Castor, which is close to its right.
Like all the stars in the night sky, Pollux and Castor rise and set about four minutes earlier each day. They and the other distant stars return to the same point in the sky every 23 hours and 56 minutes. But during that time, Earth moves a little farther in its orbit around the Sun. So Earth has to turn a little bit longer for the Sun to return to the same spot. As a result, the entire background panorama shifts position from night to night.
Gemini is at its best during winter, when it’s in view for all or most of the night. In early spring, it’s in view for about half the night. And now, as spring gives way to summer, only the twins remain in view — but not for much longer. They’ll soon vanish from the evening sky once again. But they’ll return to view a couple of months from now — this time in the dawn twilight — beginning another year-long circle across the night sky.
Tomorrow: “gentlemanly” astronomy.
Script by Damond Benningfield
This might come as a bit of a surprise, but no star is perfectly round. A star’s rotation, and the gravitational tug of any companion stars, can distort the shape. So most stars are slightly flattened. The Sun, for example, is about six miles wider through the equator than through the poles. The Sun’s average diameter is about 865 thousand miles, though, so that slight flattening isn’t noticeable. But some stars are so squashed that they look like lozenges. And still others look like eggs.
Two egg-shaped stars form the system known as Spica, the leading light of the constellation Virgo.
Both of Spica’s stars are much bigger, brighter, and heavier than the Sun. And the stars are quite close together. Their surfaces are just a few million miles apart — so close that we can’t see them as individual stars even through the largest telescopes.
Because the stars are so big, their grip on their outer layers of gas is pretty weak. And at their tight range, the gravity of each star exerts a pretty good pull on the other. That distorts the shapes of both stars — it makes them “bulge” outward. So if we could see the system up close, both stars would look like eggs, with the narrow ends pointing toward each other.
Look for Spica close to the left or lower left of the Moon as darkness falls this evening. The bright star will stand about the same distance to the right of the Moon tomorrow night.
Script by Damond Benningfield
Archaeologists know of only a few major artifacts of the pharaoh Khufu, who ruled Egypt more than 4500 years ago. The list includes some small statuettes — some of which might have been created long after his reign. But one artifact is at the opposite end of the size scale: the Great Pyramid of Giza, one of the seven wonders of the ancient world.
The pyramid was built with the help of a guiding light — the star Thuban. At the time, it was the Pole Star. It marked due north in the sky, making it a good tool for laying out the pyramid. And as the Pole Star, it was the hub of the sky, with all the other stars rotating around it — a position that held great power for many cultures.
Thuban stands due north as the sky gets dark right now. It’s in Draco, the dragon, high above today’s Pole Star, Polaris. Thuban isn’t very bright, so it’s hard to see from light-polluted cities.
Thuban lost its position as the north celestial pole because of an effect known as precession. Earth wobbles on its axis like a gyroscope that’s running down. It takes 26,000 years to complete a single wobble. During that time, Earth’s axis draws a big circle on the northern sky, so different stars take turns marking the pole.
Thuban held that position for a couple of thousand years, including the time when Khufu’s pyramid was built. It’ll return to that celebrated spot in the sky again — in about 20,000 years.
Script by Damond Benningfield
Our universe appears to be “flat” — like a sheet of paper stretching to infinity. If so, that would mean it’s finely balanced — a sort of “just right.”
Albert Einstein’s theory of gravity, known as General Relativity, allows the universe to assume one of three basic shapes. One shape is “closed” — like a sphere. In such a universe, two lights beamed out parallel to each other eventually would circle all the way around to their starting point.
Another possible shape is “open” — curved like a saddle or a really big Pringles chip. The light beams in such a universe would move away from each other for all time.
Finally, there’s a “flat” universe. Two light beams would remain parallel to each other forever — never spreading apart or coming together.
The actual geometry is dictated by the density of the universe — how much matter is packed into its space. In a closed universe, there’s enough matter for its gravity to cause the universe to collapse. An open universe would expand forever. And a flat universe would be balanced — neither collapsing nor expanding without end.
So far, the evidence supports a flat universe, although the matter isn’t completely settled.
Not surprisingly, it’s all pretty complicated. The flat universe is flat in three dimensions — after all, we see galaxies in every direction. To a cosmologist, it all makes sense — a “flat” universe that’s the same every way we look at it.
Script by Damond Benningfield
When it comes to understanding a star, it’s all a matter of perspective. The angle at which you view the star makes a big difference in what you know about it.
Consider Vega, the leading light of the constellation Lyra and one of the brighter stars in the northern sky. It’s in the northeast at nightfall, and climbs high overhead later on.
For a long time, astronomers thought Vega was about three times as massive as the Sun, and no more than a hundred million years old. So when they discovered a cloud of dust grains around Vega, they thought it might be raw material for planets.
But it turns out they were seeing Vega from a different angle than thought. We’re looking almost directly down on one of the star’s poles. That perspective makes it more difficult to measure Vega’s details.
Once they knew the correct angle, astronomers determined that the star spins so fast that it’s almost ripping itself apart. They also found that Vega’s a bit smaller than thought, and hundreds of millions of years older.
Today, perhaps the best estimate puts Vega’s age at about 455 million years. That’s too old for the dust around Vega to be making new planets. In fact, Vega appears to already have at least one planet — a giant that’s much bigger than Earth, and much closer to its star. So the dust probably is debris from collisions between asteroids or other bodies — maybe even fully grown planets.
Script by Damond Benningfield
Like a mixed litter of puppies, sibling stars don’t necessarily look alike. That can make it hard to figure out which stars are related to each other.
One example is Regulus, the heart of the lion. It’s close to the left or lower left of the Moon as darkness falls.
To the eye alone, Regulus looks like a single bright star. Instead, it’s a system of four stars — two pairs of stars that are separated by a third of a light-year.
What we see as Regulus is the brightest of the four stars. Known as Regulus A, it’s much bigger, heavier, and brighter than the Sun. It’s paired with a star that’s so faint, and so close to Regulus A, that we can’t actually see it, even with the largest telescopes. It reveals its presence only to special instruments. It’s probably a stellar corpse — a white dwarf.
The other pair is known as Regulus BC. Both of its stars are smaller, less massive, and fainter than the Sun. One of them, in fact, is less than one percent of the Sun’s brightness.
Despite the differences in the four stars, there’s evidence that they’re all siblings. They’re all about the same distance away, for example — about 79 light-years. The pairs are close enough to each other for their gravity to hold them together. And the stars move through the galaxy in the same direction, and at the same speed — indications that they’re members of a stellar family.
Script by Damond Benningfield
Our home galaxy is a cosmic melting pot. While many of its stars were born in the Milky Way, many others came from outside. They were born in smaller galaxies that were captured by the Milky Way. Over time, the smaller galaxies were ripped apart, and their stars were scattered throughout the Milky Way. And one of the Sun’s close neighbors may be an example.
Kapteyn’s Star is about 13 light-years away. Only about 20 other star systems are closer. The star is about a third the size and mass of the Sun. Don’t try looking for it, though — it’s only one percent of the Sun’s brightness, so you need a telescope to see it.
The star’s composition and motion don’t match that of the stars that are native to the Milky Way — or at least to the Milky Way’s bright disk. Kapteyn’s Star has a lower proportion of heavier elements — an indication that it’s extremely old. And it orbits the center of the galaxy in the opposite direction from most of the stars around it.
The combination suggests that Kapteyn’s Star came from the Milky Way’s halo, a vast region that surrounds the disk. In fact, there’s evidence that Kapteyn’s and a few other stars came from a giant cluster known as Omega Centauri.
It’s likely that the cluster is the core of a small galaxy captured by the Milky Way long ago. The stars in the galaxy’s outer precincts were pulled away — making them new residents of our home galaxy.
Script by Damond Benningfield
The biggest globular star cluster in the Milky Way Galaxy may not be a child of the Milky Way. Instead, it may be a sort of orphan — the surviving core of a smaller galaxy that was captured by the Milky Way.
Omega Centauri contains perhaps 10 million stars, all packed into a dense ball about 150 light-years across. In the cluster’s middle, the stars are packed so tightly that they’re only about a tenth of a light-year apart. Compare that to our part of the galaxy, where the nearest neighbor star is more than four light-years away.
The cluster appears to be about 12 billion years old — one of the older clusters in the entire galaxy. But the composition of its stars, and the way it orbits the center of the Milky Way, suggest that Omega Centauri wasn’t born here. Instead, it appears to be one of many dwarf galaxies captured by the Milky Way. Over time, the stars in the smaller galaxy’s outer regions were pulled away. So over the eons, that left only Omega Centauri’s core — a possible “orphan” adopted by the Milky Way.
Omega Centauri is about 16,000 light-years away, in the constellation Centaurus, which is quite low in the south at nightfall. If you live south of about Dallas, and you have dark skies, you might just make out the cluster as a hazy patch of light about as wide as the Moon.
We’ll talk about one of the possible escapees from Omega Centauri tomorrow.
Script by Damond Benningfield
As you look out into the night sky, you might think that you’re seeing a true sampling of the stars — in other words, a little of everything. That’s not the case, though. Most of what you see is the Milky Way’s equivalent of the one percenters — stars that are among the galaxy’s biggest and brightest.
An example is in the constellation Centaurus, which wheels quite low across the south on June nights. It’s so low, in fact, that much of it stays below the horizon for those of us in the United States. That includes its brightest star, Alpha Centauri.
The brightest star most of us can see in Centaurus is Menkent, a name that means “the shoulder of the centaur.” It’s due south at nightfall.
Like many of the other stars that are visible to the unaided eye, Menkent looks so bright because it’s nearing the end of its life. It’s converted the original hydrogen fuel in its core to helium. That’s made the core get smaller and hotter, which in turn made the star’s outer layers puff up. Today, Menkent is more than 10 times wider than the Sun, and about 60 times brighter.
Dying stars like Menkent are rare. Most of the stars in the galaxy are still in the prime of life, so they’re not as bright as they’ll become later on. But because stars like Menkent are so big and bright, they’re greatly over-represented in the stars we see — stellar giants glowing brightly in the night sky.
Script by Damond Benningfield
Earth lies in the middle of the Sun’s habitable zone. That’s the distance from the Sun where conditions are most comfortable for life. And astronomers are concentrating their hunt for life in other star systems in their habitable zones.
There’s an idea that galaxies have habitable zones as well. The zones would have a good mix of chemical elements, not too much radiation, and a low risk of exploding stars.
Stars consist mainly of hydrogen and helium. But to make planets like Earth, you need a good supply of heavier elements — things like oxygen, silicon, and iron. Those elements are forged in the hearts of stars, then blown out into space when the stars die. So to have good conditions for life, you need a region where lots of dead stars have “seeded” the galaxy with heavy elements.
But you don’t want to be too close to stars that die in massive explosions. They can damage a planet’s atmosphere, exposing life to high levels of radiation. So you want to be away from a galaxy’s core, where stars are packed close together — including ones that might explode.
The cores of most galaxies also harbor supermassive black holes. As they pull in stars and gas they produce lots of radiation, saturating the space around them.
So in our home galaxy, the Milky Way, you want to be away from the core, but not too far away. And that’s just where Earth is — about half way from the center to the edge — in the galactic habitable zone.
Script by Damond Benningfield
A possible new space telescope probably won’t launch for a couple of decades, if at all. But astronomers are already looking for targets for it to study — star systems with planets that could host life.
Habitable Worlds Observatory will have several jobs. As the name suggests, one of those jobs will be to scan planets for signs of life. The telescope will screen out the light from a star, allowing it to take pictures of planets around the star.
Most important, the telescope will analyze the atmospheres of planets in the habitable zone — the region around a star that’s most comfortable for life. The telescope’s instruments will look for oxygen, ozone, methane, and other substances that are pretty good signs of life.
Early estimates say the telescope will cost more than 10 billion dollars, so scientists don’t want to waste any of its time. So they’re already compiling a list of star systems with candidate planets, using findings from many telescopes in space and on the ground.
And they’re trying to learn as much as possible about the systems. They want to know if the orbits of the habitable-zone planets are stable, for example; planets with unstable orbits might not have been in the zone long enough for life to develop.
The list of possible targets already has dozens of planetary systems. But the search continues — for planets that might tell us if there’s life elsewhere in the universe.
Script by Damond Benningfield
Many factors are involved in making a planet habitable: the size and composition of the planet, the stability of its orbit, its distance from its star. But scientists are still trying to figure out which factors are important.
An example is plate tectonics. Earth’s surface is divided into large “plates.” They glide along the rocks below the surface. They ram together, slide over each other, and recycle the crust. They allow heat to escape to the surface, and affect the chemistry of the atmosphere. So tectonics has been considered a key ingredient for the development of life.
But some recent studies have cast some doubt on that idea. One study found that the early Earth probably didn’t have tectonics. Instead, its crust was rigid — a “stagnant lid.” Instead, molten rock would have punched through the crust, building big volcanoes. That warmed the surface, allowing the development of the first life more than three and a half billion years ago. But the study also suggested that tectonics might be necessary to sustain life, and allow the development of more complex life.
But another study disputes even that. It says that life could last for billions of years on a stagnant-lid planet.
Some models show that plate tectonics could be rare on other planets. But if tectonics isn’t necessary for life, then the number of possibly habitable worlds goes way up — increasing the chances that we might find a “living” planet.
Script by Damond Benningfield
It’s pretty remarkable that scientists have figured out that some meteorites come from Mars. What’s even more remarkable is they may know just where on Mars one of them came from.
The meteorite is cataloged as Northwest Africa 7034. It was discovered in 2011, in the Sahara Desert. The rock weighs about 11 ounces. And because of its dark appearance, it’s nicknamed “black beauty.” An American bought the meteorite and donated it to the University of New Mexico.
Detailed analysis revealed that it came from Mars. And it contains the oldest bits of Mars yet seen: small crystals almost four and a half billion years old — almost as old as Mars itself.
Studying the meteorite can help scientists learn about the formation of Mars. But it helps to have more background about the meteorite. So geologists set about trying to find out where it came from. They used A-I to study millions of impact craters. They compared the types of craters, the composition of their rocks, and their magnetic fields. And they came up with a likely location: near a large crater in the southern hemisphere.
The rock likely was blasted from below the surface when an asteroid hit Mars one and a half billion years ago, gouging out a crater 25 miles across. The rock stayed on the surface until a smaller impact hurled it into space 5 to 10 million years ago. It then made its way to Earth — the oldest bits of Mars we’ve ever seen.
Script by Damond Benningfield
The landing sites of the two most recent American Mars rovers are about 2300 miles apart — roughly the distance from Los Angeles to Washington, D.C. Yet the sites are a lot alike. Both are inside impact craters that formed at least three and a half billion years ago. And both craters once held lakes — potential homes for microscopic life.
Curiosity landed in Gale Crater, in 2012. The crater is almost a hundred miles across, with a central mountain that’s three and a half miles high.
Curiosity has found that water could have filled the crater several times in its early history. Some of the lakes could have lasted for millions of years. Eventually, though, Mars lost most of its atmosphere, and the water on its surface disappeared.
Perseverance landed in Jezero Crater, in 2021. It’s a little less than 30 miles in diameter. But it, too, could have been filled up several times, with some of the lakes possibly hundreds of feet deep. At least one of the lakes formed when a massive flood ripped through the crater’s rim. It created a large river delta that Perseverance continues to explore.
Neither rover has found evidence of life. But they’ve revealed that both craters could’ve had the right conditions for life — billions of years ago.
Look for Mars well to the upper right of the Moon at dawn tomorrow. It looks like a bright orange star. More about Mars tomorrow.
Script by Damond Benningfield
The Perseverance Mars rover packs a laser gun. It’s not for defense against Martians. Instead, it’s a scientific instrument — a way to learn about Martian rocks without drilling into them. And the sound of the laser helps in that effort.
Perseverance zaps a target rock dozens of times in just a few seconds. That vaporizes some of the rock. The rover’s instruments analyze the composition of the vapor. That reveals the chemistry of the rock. Scientists use that information to infer something about how the rocks formed, and about the conditions on Mars when they formed.
A microphone on the rover records the sounds of the laser impact on the rocks. And the sound is different for different types of rocks. Scientists have used that difference to estimate the hardness of the rocks. And they combine the sounds with their analysis of the gas from the laser shots to measure the mineral composition of the rocks. So the eyes — and ears — of Perseverance are telling us a lot about the history of the rover’s location on Mars.
Look for Mars in the dawn sky. It looks like a fairly bright orange star, low in the east at first light. Tomorrow, the planet will stand close to the upper right of the Moon. Mars will climb a little higher into the morning sky as spring ends and we head into summer.
We’ll have more about Mars tomorrow.
Script by Damond Benningfield
There might be three ways to build a habitat on the Moon or Mars. You could bring along everything you need for the habitat from Earth. You could build it from local materials. Or, according to one NASA research team, you could grow it — using fungi.
The team has been working on the technique for years. It uses mycelia — the part of a fungus that grows out of sight. It’s tough, and it can form large networks of interlocking threads. And it can grow quickly.
Researchers have come up with several possible ways to use mycelia. One would be mixing it with the dirt on the Moon or Mars to make bricks. Another would be to make a layered structure, with water ice, the fungi, and a type of algae. And yet another would use an inflatable structure, with “baked” mycelia forming rigid walls and algae producing oxygen to inflate it.
For Mars, the mycelia would have to be engineered in a way that it couldn’t escape and take root on the Red Planet — potentially destroying evidence of any microscopic life there.
So there’s still a lot of work to be done before anyone can produce a “fungal growth” on the Moon or Mars.
The two worlds are close together in the early morning sky the next few days. Mars looks like a bright star. It will stand to the lower left of the Moon at dawn tomorrow, and about the same distance to the upper right of the Moon on Monday.
We’ll have more about Mars tomorrow.
Script by Damond Benningfield
At heart, just about every star is a potential cannibal. Stars that travel through space alone don’t get the chance to act on that instinct. But those with close companions sometimes do act on it. They can pull gas from the companion, eventually leaving the companion with no more than its hot core.
A recent study found a handful of such systems. Three of them are in Cygnus, the swan. One example is called 60 Cygni.
Its two stars are about as far apart as Mars and the Sun. The main star appears to be more than 10 times as massive as the Sun. It’s also much hotter and brighter than the Sun. The companion appears to be a stripped-down core — its outer layers have been cannibalized by the heavy star.
When the system was born, the stripped star probably was the more-massive member. As it reached the end of the prime phase of life, it puffed up. That allowed the companion to start pulling away some of the dying star’s outer layers of gas. Eventually, all of the material in the outer layers might have been transferred to the other star, making it the bigger member of the duo.
In time, that star will begin to expand as well. So the stripped-down companion may begin to pull away its outer layers — cannibalizing the cannibal.
Cygnus is low in the northeast not long after the sky gets good and dark. But you need binoculars or a telescope to find its possible cannibals.
Script by Damond Benningfield
Planetary scientists can hardly move these days without splashing into a new ocean — or at least a possible one. They’ve discovered that oceans of liquid water may be hidden below the icy crusts of many smaller bodies: several moons of the giant planets, the largest member of the asteroid belt, and even remote little Pluto.
One of the more recent “ocean worlds” may be Mimas, a moon of Saturn. It’s less than 250 miles in diameter. Its main feature is a giant impact crater. It’s so big that it makes Mimas look like a “death star” from Star Wars.
Mimas is pockmarked by a lot of craters. Many of them are so old that scientists had thought the little moon was dead, with nothing happening inside it. But precise measurements of Mimas’s orbit and its rotation on its axis revealed some odd “wobbles.”
Scientists proposed a liquid ocean as a possible explanation for those wobbles as early as 2014. A study released earlier this year solidified the case. It found that the ocean could lie 15 miles or so below the surface, and account for up to half of the moon’s volume. The ocean would have formed no more than 25 million years ago. That’s not enough time for evidence of it to show up on the surface. So the ocean remains hidden deep inside this “death-star” moon.
Look for Saturn especially close to our own moon in the wee hours of tomorrow morning. It looks like a bright star just above the Moon at dawn.
Script by Damond Benningfield
Most people keep their hands as far from snakes as possible. But handling a snake was the job for the mythological serpent bearer. He’s represented in the stars as the constellation Ophiuchus, which is in the east and southeast at nightfall. The head of the snake is above Ophiuchus, with its tail below.
In one story, the constellation represented a serpent god. In another, it was a god wrestling with a snake. And in still another, it was an ancient healer who learned the secret of life by watching snakes.
His left hand — the one holding the snake’s head — is represented by two stars: Yed Prior, which leads the way across the sky, and Yed Posterior.
In our sky, the stars are separated by less than the width of your finger held at arm’s length. But they’re not related. One is a little more than a hundred light-years away, while the other is about 160 light-years.
Both stars are more massive than the Sun. So even though they’re much younger than the Sun, they’ve already moved past the prime of life. They’ve burned through the hydrogen fuel in their cores. That’s caused their outer layers to expand to giant proportions. So they’re many times bigger and brighter than the Sun.
Yed Prior and Yed Posterior are about a quarter of the way up the east-southeastern sky at nightfall, with Yed Prior slightly higher. Under even moderately dark skies, they’re easy to see — outlining the hand of the serpent bearer.
Script by Damond Benningfield
The giant families of stars known as globular clusters are like carnival rides: They do a lot of bobbing up and down. And they may lose a bit of themselves with every gyration.
An example is the cluster Messier 12. It’s probably more than 16,000 light-years from Earth. It contains a couple of hundred thousand stars, all packed into a ball about 75 light-years across. That means the stars are much closer together than the stars in our part of the galaxy.
Like all globulars, M12 travels at an angle to the Milky Way’s disk. So it periodically passes through the disk. During each pass, the gravity of the disk may pull away some of the stars on the outskirts of M12.
A study a couple of decades ago found a lack of lower-mass stars in the cluster. Heavier stars tend to congregate in a cluster’s core, where they’re held fast by the gravity of the other stars around them. Less-massive stars migrate to the outskirts, where they’d be easy to pull away.
Today, M12 contains about 200,000 stars. But it could have lost several times that number over its 13-billion-year lifetime. So as many as a million of the cluster’s stars might now be orbiting the center of the galaxy on their own — pulled away from their birthplace.
Messier 12 is in Ophiuchus, the serpent bearer, which is in the east and southeast at nightfall. But you need a telescope to see this possibly vanishing cluster of stars.
Script by Damond Benningfield
The Sun is about four and a half billion years old, so it’s been around awhile. Compared to some of the galaxy’s oldest stars, though, it’s a youngster. Some stars have been around since shortly after the universe was born.
In the Milky Way Galaxy, many of those ancient stars reside in globular clusters — giant balls of stars that may have formed as the Milky Way itself was taking shape.
An example is Messier 5. It’s in the southeast at nightfall, in the constellation Serpens. It’s a bit too faint to see with the eye alone, but through binoculars it looks like a fuzzy star.
M5 is about 25,000 light-years away. It contains several hundred thousand stars. Together, they form a slightly flattened ball that spans about 160 light-years.
Most of the stars in M5 formed at about the same time, from a single giant cloud of gas and dust. Those stars are about 12 billion years old, and perhaps older.
Almost all of its stars are fainter and less massive than the Sun. Only a few are more impressive — stars that are in the final stages of life, or that’ve been “rejuvenated” by encounters with other stars. Any stars that were born heavier than the cluster’s current population have either exploded or shed their outer layers to expose their hot, dead cores — the remnants of some of M5’s most ancient stars.
Script by Damond Benningfield
The head of the serpent slithers into the early evening sky this month, with its tail twisting along a bit later.
Serpens is the only constellation that’s split apart. The two halves are separated by Ophiuchus, the serpent bearer. The snake’s head rises first. It’s in the east and southeast at nightfall, marked by a serpentine trail of faint stars. The tail, which is below Ophiuchus, climbs into view about an hour later.
The brightest of the stars of Serpens is Unukalhai — an Arabic name that means “the serpent’s neck.” The star also is known as Alpha Serpentis, indicating its ranking as the constellation’s leading light.
The star is in the final stages of life. It converted the hydrogen fuel in its core to helium, causing the core to shrink and get hotter. That triggered the next round of nuclear reactions, with the helium being converted to carbon and oxygen.
The changes in the core have caused the star’s outer layers to puff up like a balloon. That’s made the star about 14 times wider than the Sun. The expansion also made the star’s surface much cooler, so it shines yellow-orange.
In time, all the reactions in the star’s core will stop, and the outer layers will puff out into space. For a while, that expanding cloud will form a colorful bubble. As the bubble cools and dissipates, though, only the star’s dead core will remain — depriving the serpent of its bright neck.
More about the serpent tomorrow.
Script by Damond Benningfield
Aiello del Friuli is a village in northern Italy, about 75 miles from Venice. It’s home to about 2200 residents and more than a hundred sundials — so many that it’s known as the “village of sundials.” It hosts a sundial festival every year, in late May.
The village began earning the nickname in 1994. A resident created a sundial and hung it on the side of his house. It was more than just a pointer and some numbers, though — it was a work of art. So others in the village asked him to make sundials for their homes. He obliged. And before long, other artists got into the act.
Today, the sundials are spread all across town. There are more than 20 in a plaza next to a museum, but they’re in all the neighborhoods as well. Like the original, many of the sundials are mostly two-dimensional and are displayed on building walls. But some are more three-dimensional — globes, bowls, and other shapes mounted on their own.
The sundials follow many artistic themes. Some have religious or historic significance. Others depict nature or agriculture, or have a more abstract quality. And the bounty keeps on growing. The annual festival includes a contest for the best sundial created during the previous year.
All of the sundials also do a job: They track the time as the Sun crosses the daytime sky in the “village of sundials.”
Tomorrow: the head of the serpent wriggles into the evening sky.
Script by Damond Benningfield
Black holes are the darkest objects in the universe — they produce no light at all. Yet they power some of the brightest objects. Known as quasars, these beacons can outshine entire galaxies of hundreds of billions of stars. In fact, the brightest one seen so far emits more light every minute than the Sun will produce in its entire 10-billion-year lifetime.
A black hole’s gravity is so powerful that nothing can escape from it — not even light. But before anything disappears into the black hole, it enters a disk that spirals around the black hole at a good fraction of the speed of light. That creates friction, which heats the material to millions of degrees. The disk emits enormous amounts of radiation, so it shines brightly at many wavelengths.
Quasars are disks around supermassive black holes in the hearts of galaxies. And the brightest one yet seen is truly a monster. It encircles a black hole that appears to be about 17 billion times the mass of the Sun. The black hole is gulping the equivalent of a star as massive as the Sun every day. That creates a disk that’s hundreds of millions of miles across. It shines thousands of times brighter than our entire Milky Way Galaxy.
We see the quasar as it looked more than 12 billion years ago — not long after the birth of the universe. So by now, it’s probably shut down — turning off one of the most brilliant lights we’ve ever seen.
Script by Damond Benningfield
Stars like the Sun aren’t massive enough to become black holes when they die. But there’s a possible exception to that rule: if the star is born with a small black hole inside it. The idea was first proposed by Stephen Hawking. And it’s supported by a recent study.
Normally, a star like the Sun just isn’t massive enough to collapse to make a black hole.
But the universe might be sprinkled with black holes created in the Big Bang. Such black holes could be just about any mass — from almost nothing, to as heavy as a star.
Such a black hole could be incorporated into a newly forming star. There, it would slowly “eat” the star from the inside. Over time, that process could account for some of the star’s energy production. But the black hole might reach a tipping point where it would gobble the rest of the star — converting the whole thing into a black hole.
Measuring the vibrations at the surfaces of Sun-like stars might reveal the presence of black holes inside them — eating them from the inside.
The new study says that a black hole up to about one millionth of the Sun’s mass could be at work inside the Sun today. If it’s there, within a hundred million years it could cause the Sun to drop to about half of its current brightness. The Sun then would puff up to many times its current size, and shine brighter for billions of years. After that, it would collapse to form a black hole.
More about black holes tomorrow.
Script by Damond Benningfield
Our brains can see things that aren’t there. They connect points and shapes to create “pictures.” So we might see a dragon in some puffs of clouds, “canals” on the surface of Mars, or a scorpion in the stars.
One of the most persistent pictures is the “man in the Moon” — a face created from features on the lunar surface. Stories about the man in the Moon — or, in some cases, the woman in the Moon — go back centuries, from cultures around the planet.
In China, for example, the face represented the goddess Chang’e. She was stranded on the Moon after taking too much of a potion that made her immortal. In Germany, the man was a giant who poured water from the Moon to create high tides. And in parts of Europe, the man was banished to the Moon after he stole from a neighbor or worked on the Sabbath.
Today, inns and pubs from Tokyo to the Isle of Wight are called Man in the Moon. It’s been the title of several books. And in the first science-fiction movie, in 1902, a rocket from Earth slammed into the man’s “eye,” with messy results.
The features that make up the man’s face are a combination of dark, smooth volcanic plains, and lighter areas that are more jumbled. You can look for the face yourself the next couple of nights because the Moon is full. And it has a bright companion: The star Antares is to the lower left of the Moon this evening, but almost touching the Moon tomorrow night.
Script by Damond Benningfield
The Moon is in a sort of cosmic balance tonight. It’s passing through Libra, the balance scales — the only constellation of the zodiac that doesn’t represent a living thing.
But the scales are associated with two living things — Virgo, which represents a goddess, and Scorpius, the scorpion. In various cultures of the Mediterranean, the stars of Libra were attached to one or both of those figures.
In ancient Babylon, the stars represented a scale held by Shamash, the Sun god. He was also the god of truth and justice. The scales helped him maintain a “balance” on Earth and in the heavens.
And there may have been an astronomical reason for thinking of the stars of Libra as “in balance.” Until about 2700 years ago, the Sun passed across those stars at the fall equinox — a time when day and night are roughly the same length — they’re in balance.
Libra also was identified as the claws of the scorpion, which is on the opposite side of the constellation. The names of Libra’s brightest stars still reflect that heritage: Zubeneschamali, the northern claw, and Zubenelgenubi, the southern claw, which is quite close to the Moon tonight.
The Greeks maintained the connection to both the gods and the scorpion. Libra wasn’t depicted as a separate constellation until a couple of thousand years ago, in Rome. Yet it maintains the links to its heritage — the scales of justice, and the claws of the scorpion.
Script by Damond Benningfield
One of the icons of classic western movies is the sunset. Even in black and white, rays of sunlight radiate into the sky like jets of water erupting from a fountain. They add a bit of grandeur to any sunrise or sunset.
They’re known as crepuscular rays, from the Latin word for twilight. Technically, the name applies to rays that appear during morning or evening twilight, while the Sun is below the horizon. In modern usage, though, it applies to rays of sunlight shining from behind clouds or other obstacles at any time of day.
The bright rays alternate with darker shadow bands, where clouds or mountains block some of the sunlight. The rays appear to radiate in all directions. But that’s an illusion. All of the rays are parallel. They appear to converge on the Sun because of perspective. It’s like looking down a set of railroad tracks. The tracks appear to converge as you look farther away, even though they’re the same distance apart. In the case of crepuscular rays, they all converge at the Sun.
We see the rays because they scatter off small particles in the atmosphere, such as grains of dust or pollen. The rays usually look yellow or orange, and for the same reason the twilight sky shows those colors: Air molecules scatter most or all of the blue light, leaving the redder wavelengths to shine through — adding some golden rays to any sunrise or sunset.
Script by Damond Benningfield
When astronomers look at Spica, they see double. Or at least their instruments do. The system consists of two stars. But they’re so close together that even the biggest telescopes see them as a single point of light. So it took a technique called spectroscopy to “see” the system as a binary.
The technique splits the light from a star into its individual wavelengths. Each chemical element imprints its own “barcode” in that spectrum of light.
In the case of Spica, there are two sets of those barcodes. And they shift back and forth a tiny bit — the result of the orbital motion of the stars around each other.
Careful study of the two spectra has revealed many details about the system.
For example, the main star is much bigger and more massive than the Sun. It’s destined to explode as a supernova. The other star isn’t quite as impressive, but still far more impressive than the Sun. It probably won’t explode, but instead will leave a small but heavy corpse.
The stars orbit each other once every four days. Their surfaces are only a few million miles apart — so close that the gravity of each star distorts the shape of the other — one more amazing finding about this impressive double star.
To the eye alone, Spica looks like a single bright star. Tonight, it’s close to the lower left of the Moon at nightfall. The Moon slides toward it during the night, so they’re especially close as they set, in the wee hours of the morning.
Script by Damond Benningfield
A horse and rider gallop across the north and northwest on May evenings. They’re in the handle of the Big Dipper, which is high in the sky at nightfall and low in the northwest at dawn.
They’re the stars Mizar and Alcor. Mizar is the brighter of the two, with fainter Alcor just a whisker away. They’re so close together that the skywatchers of bygone centuries thought of them as a horse and rider.
Mizar is a system of four stars, all of which are a little hotter and brighter than the Sun. Alcor consists of two stars — one of them more impressive than the Sun, the other less impressive. Both systems lie about 80 light-years from Earth.
One question that astronomers have asked for centuries is whether the two systems are bound to each other, or if they just happen to line up in the same direction in the sky.
They’re both members of a wide-spread cluster. That makes Mizar and Alcor stellar siblings — they formed at the same time, from the same cloud of gas and dust.
Just how close their relationship is has remained a mystery. Early observations said the systems were perhaps two or three light-years apart. At that range, they probably would not be gravitationally bound to each other.
But observations over the past few years by the Gaia space telescope put the separation at roughly one light-year. That may be close enough for them to be saddled together as a single unit — just like a horse and rider.
Script by Damond Benningfield
Millions of black holes inhabit our home galaxy, the Milky Way. Most of them probably roam the galaxy alone, so we never see them. Luckily for science, though, many of them have companion stars. That makes it possible for astronomers to “see” and learn about the black holes.
An example is a system called Swift J1357. It was discovered in 2011 by Swift, a space telescope that studies the X-ray sky. The system is thousands of light-years away, and appears to be outside the galaxy’s disk of stars.
J1357 consists of two objects: a black hole and a small, faint companion star. The black hole’s gravity pulls in hot gas from the companion. The gas spirals around the black hole, heating up and forming a faint disk.
The black hole appears to be at least nine times the mass of the Sun. It and the companion orbit each other once every two and a half hours — one of the tighter orbits of any known black-hole binary system.
J1357 produces outbursts of X-rays every few years. They may occur when too much gas piles up in the disk. It gets so hot that it causes an eruption of particles and energy — an outburst that reveals more about this intriguing system.
Swift J1357 is much too faint to see with the eye alone, but we can spot its location. It’s close to the left of Spica, the brightest star of Virgo. It’s about a third of the way up the southeastern sky at nightfall.
Script by Damond Benningfield
Jupiter is missing. The solar system’s biggest and heaviest planet is nowhere to be seen. And it won’t return to view for a few weeks.
Jupiter is passing behind the Sun as seen from Earth, so it’s hidden in the Sun’s brilliant glare. It’ll be closest to the Sun on Saturday afternoon. That point is known as conjunction, and it happens every 12 and a half months.
Jupiter is known as a “superior” planet. That means its orbit is outside Earth’s orbit around the Sun. So Jupiter sometimes lines up directly opposite the Sun in our sky, shining brightly all night long. About half a year later, though, it passes behind the Sun and out of sight.
The planet doesn’t necessarily pass directly behind the Sun. This time, for example, it slides about half a degree from the Sun — less than the width of your finger held at arm’s length. Even so, it’s so close to the Sun that astronomers can’t point their telescopes toward it. And radio “static” from the Sun means that flight controllers lose contact with spacecraft at Jupiter for a while. The craft operate on their own, and save their observations to beam to Earth when the Sun is out of the way.
For casual skywatchers, Jupiter should return to view in a month or so. It’ll be quite low in the eastern sky during the dawn twilight. It’ll be in better view as we move into summer — climbing farther from the Sun, and shining like a brilliant beacon in the early morning sky.
Script by Damond Benningfield
The Moon and the heart of the lion stand close together this evening. The lion’s heart is the star Regulus, to the lower right of the Moon at nightfall.
We see Regulus and the Moon for different reasons. Regulus is a star — a brilliant ball of hot gas. It generates its own light — so much light that it’s visible across almost 80 light-years. That means we see Regulus as it looked almost 80 years ago. So if anything big were to happen to the star tonight, Earth wouldn’t know it until early in the 22nd century.
The Moon doesn’t produce any light of its own. Instead, it reflects sunlight. The Moon looks big and bright only because it’s far closer to us than any other celestial object — an average of about a quarter of a million miles. That’s a bit more than one light-second, so we see the Moon as it looked a bit more than one second earlier.
Tonight, the Sun lights up a little more than half of the lunar hemisphere that faces our way. Many people think of that phase as a “half” Moon. And based on its appearance alone, that’s perfectly correct.
But a “half” Moon is also known as a quarter Moon. And at the current angle, it’s the first quarter Moon. That may sound confusing, but there’s a simple explanation: At first quarter, the Moon is one-fourth of the way through its month-long cycle of phases. It’s half of the way through the cycle when it’s full. And the cycle starts over at new Moon — when it’s not visible at all.
Script by Damond Benningfield
A binary star system about 30 million light-years away is an impostor. When astronomers first saw it, they thought it was a supernova — the titanic explosion of a massive star. They even called it one: Supernova 2000ch. But the system is still there.
The system is in the spiral galaxy NGC 3432, in a clump of young, bright, heavy stars.
By the end of last year, 2000ch had produced 23 outbursts. They’ve been about six and a half months apart. Based on that interval, the way the system brightens and fades, and other details, astronomers have developed a model of what’s going on.
The system’s main star is dozens of times the mass of the Sun, and a million times brighter. It’s also unstable — it puffs in and out.
A smaller companion star follows a lopsided orbit. During its close approaches, it stirs up the brighter star, triggering an outburst. And if the main star is in its “puffier” phase, then the outburst is especially bright.
The system may be building up to a much bigger outburst in the fairly near future. And after that, the massive star could explode as a supernova — no longer an “impostor,” but the real thing.
NGC 3432 is in Leo Minor, the little lion. It’s too faint to see without a telescope. But it’s high above the Moon as darkness falls tonight. The bright star Regulus — the heart of the big lion — is to the left of the Moon. More about that meeting tomorrow.
Script by Damond Benningfield
Beta Pictoris is one of the more famous of all star systems. It’s also one of the most complex. It includes a young star, at least two giant planets, lots of gas and dust, and a “cat’s tail” that might be the result of a giant impact.
The star is almost 65 light-years away. It’s about twice as big and heavy as the Sun, and almost 10 times as bright.
In 1983, an infrared space telescope discovered a disk of gas and dust around Beta Pic. It spans hundreds of billions of miles, and contains several wide belts. The belts may consist of debris left over from the collisions of comets and asteroids.
Gaps between the belts contain two known planets. Both of them are more than 10 times the mass of Jupiter, the giant of our own solar system. One of them orbits the star once every three and a third years; the other, once every 24 years.
A smaller second disk also encircles Beta Pic. Last year, Webb Space Telescope discovered a “cat’s tail” of debris curling away from it. It might have formed about a century ago, when a collision between giant chunks of rock and ice shattered the bodies, splashing debris up and away from the disk.
Beta Pictoris is still an infant — it’s only about 25 million years old. So the building blocks around it could still be coming together to make more planets, while others could be destroyed in more big collisions — adding to the complexity of this well-known star system.
Script by Damond Benningfield
The Moon passes especially close to the star Pollux tonight — the brighter “twin” of Gemini. The star stands just to the right of the Moon at nightfall. The other twin, Castor, is farther along the same line.
The Moon always passes closer to Pollux than to Castor. That’s because of the relationships of the three bodies to the ecliptic — the Sun’s path across the sky.
The Moon’s orbit is tilted a bit with respect to the ecliptic. Over the course of a month, it meanders to either side of the ecliptic. And over a period of almost two decades, its maximum distance from the ecliptic varies as well. At most, the Moon can appear 6.6 degrees from the ecliptic — the width of three fingers held at arm’s length. So the Moon can pass close to, or even cover up, any star or planet within that distance from the ecliptic.
Pollux and Castor are outside that zone. Pollux is 6.7 degrees from the ecliptic, while Castor is about 10 degrees away. So the Moon can sometimes appear to almost touch Pollux, while always keeping a little bigger gap with Castor.
Over millennia, the ecliptic shifts with respect to the background of stars. So for thousands of years, the Moon could sometimes pass in front of Pollux, hiding it from view. That last happened about 2100 years ago. Pollux will move back into the Moon’s range in about 10,000 years — setting up some especially close encounters.
Script by Damond Benningfield
It’s hard to think of the White Sands region of New Mexico as confining. It covers thousands of square miles, and few people live there. In the late 1940s, though, the U.S. military was feeling hemmed in. It was launching rockets from White Sands. They could go high, but they couldn’t go very far without flying over towns or cities — a possible danger to residents.
So Congress passed a bill establishing the Joint Long-Range Proving Ground at Cape Canaveral, on the Atlantic coast of Florida. President Harry Truman signed it into law 75 years ago today.
“The Cape,” as it’s been known for most of those years, offered many advantages. The region had a small population, the climate wasn’t too extreme, and there were thousands and thousands of miles of ocean to plop rockets into. Launches to orbit have benefited from its southern location — rockets get a “boost” from Earth’s rotation.
It took a year to clear away some of the scrub and build the early launch pads. The U.S. Army launched its first rocket there in July of 1950 — an American-built version of the German V-2 terror weapon.
Since then, thousands of rockets have taken flight from the Cape and the facilities on nearby Merritt Island. They’ve sent satellites into orbit, astronauts to the Moon, and probes to all the planets of the solar system — and beyond. And today, the facilities are busier than ever — at the first American spaceport.
Script by Damond Benningfield
Science and science fiction can intertwine in some interesting ways. Consider krypton — the chemical element and the fictional planet.
The element was discovered in 1898. It makes up a tiny fraction of Earth’s atmosphere — about one part in a million. It’s colorless, odorless, and tasteless. And it almost never reacts with other matter. It’s used in some fluorescent light bulbs and in lasers.
In 1938, the creators of “Superman” needed a home planet for their visitor from another world. They named it Krypton, after the element, and wrote that the planet had exploded.
As scientists learned more about how elements form, they calculated that krypton must be forged in supernovas — the explosions of massive stars. The immense energy smashes together atoms to make heavier ones. The elements are fired into space, where they can be incorporated into new stars and planets. And that’s where Earth’s krypton came from. Some is in the air, but a little bit is found in the solid planet.
A few years ago, scientists studied some radioactive forms of krypton far below the surface. The krypton matched that found in meteorites. The scientists concluded that big space rocks brought not only krypton, but water, carbon, and other essential ingredients as Earth was taking shape.
So an element found on Earth and immortalized in the comics came from exploding stars — and played a role in learning about the formation of Earth.
Script by Damond Benningfield
The names of the stars that are visible in the night sky can be obscure. But that’s not the case for the star known as Elnath. The name comes from Arabic, and it means “the butting one.” That makes perfect sense when you consider that it forms the tip of one of the horns of Taurus, the bull. It’s the second brightest star in the constellation.
Elnath is quite impressive. It’s about five times the mass of the Sun, more than four times wider than the Sun, and about 700 times brighter. Its surface is much hotter than the Sun’s, so Elnath shines almost pure white. And the star is only about 100 million years old, compared to four and a half billion years for the Sun.
Look for Elnath near the crescent Moon the next couple of nights, quite low in the early evening sky. It’s above the Moon tonight, and closer to the lower right of the Moon tomorrow night.
Elnath was the favorite star name of Sandy Wood, my predecessor as the host of Star Date. After first hearing the name, she jokingly decided that she wanted to be called “the butting one,” and often signed her emails to colleagues as simply “Nath.”
Sandy passed away earlier this year. She was with Star Date for 28 years and more than 10,000 episodes. She won fans around the country and around the world. Her warmth, kindness, and giddy sense of humor were legendary. A friend and colleague perhaps described her best: She was joy in human form. Sandy Wood will be missed — and remembered.
Script by Damond Benningfield
It’s easy to see pictures in the night sky. Just pick out some stars and connect them to make a pattern. The skywatchers of ancient Babylon linked some stars to show a man pouring water from a jar. Today, that picture is known as Aquarius, the water bearer. The constellation is in the east-southeast before dawn.
Near the left side of the constellation, you’ll find a much smaller star picture: a bowling ball scattering some pins. The ball is the planet Saturn, which looks like a bright star. And the pins are represented by five stars of Aquarius. The stars are faint, so you need dark skies to see them, and binoculars will enhance the view.
The brightest of the five stars is to the upper left of Saturn by less than the width of a pencil held at arm’s length. Phi Aquarii consists of two stars. The brighter one is about as massive as the Sun, but many times larger. That’s because it’s billions of years older than the Sun, so it’s moved from the prime life into the next phase.
About the same distance to the lower right of Saturn is Chi Aquarii. It’s a giant as well, but even bigger and brighter. That makes it visible across 600 light-years of space.
Finally, three stars are a little farther along that line —Psi 1, 2, and 3 Aquarii. The brightest is number one — a triple star 150 light-years away.
Saturn will roll past the stars over the coming days — leaving some faint “bowling pins” behind.
Script by Damond Benningfield
In our region of the Milky Way Galaxy, the stars are a long way apart. The Sun’s nearest neighbor is more than four light-years away — 25 trillion miles. In the core of a globular cluster, though, the stars are packed hundreds of times more densely. That means the stars are only a few light-months apart, or even light-weeks — much closer than in our own neighborhood.
One of the most prominent globular clusters is in Hercules, the strongman. M13 — the Hercules Cluster — is perhaps 25,000 light-years away. It contains several hundred thousand stars.
M13 and the other globular clusters are thought to be the oldest inhabitants of the Milky Way. So most of the stars in the cluster are more than 10 billion years old — more than twice the age of the Sun.
Such stars are fainter, redder, and less massive than the Sun. From a planet near the cluster’s middle, you’d see a whole bunch of stars in the night sky, and almost all of them would be yellow, orange, or red — remnants of the early galaxy.
M13 is low in the northeast at nightfall. It’s along the line that connects the top two stars in the “Keystone” — a lopsided square of stars that outlines the strongman’s torso. Under clear, dark skies, the cluster looks like a dim fuzzball. It’s easier to see if you look out of the corner of your eye. It’s an easy target for binoculars — the glow of an ancient family of stars.
Script by Damond Benningfield
The geography of the sky owes a lot to Claudius Ptolemy. He was a Greek astronomer who lived and worked in Alexandria, the capital of Greek-controlled Egypt.
Almost 1900 years ago, Ptolemy published one of the most important astronomical works in history. Known as the Almagest, it contained Ptolemy’s models of the motions of the Sun, Moon, and planets, and much more. One of its most important features was a catalog of stars and constellations. It listed 48 constellations visible from the northern hemisphere, most of which had been around for thousands of years. And, thanks to Ptolemy, they’re still with us today.
The list includes Hercules, the strongman. The constellation is in the east and northeast at nightfall, and swings high overhead during the night.
“Hercules” is the Roman version of Heracles, a son of Zeus, the king of the Greek gods of Olympus. His mother was not Zeus’s wife, Hera, and Hera wasn’t happy about the situation. She tried to kill the baby, but he survived. She then set about making his life miserable.
Hera drove the adult Heracles mad, causing him to kill his family. To atone for his crimes, he was given 12 labors to complete — tests of strength, courage, and skill. Eventually, Hera relented, and allowed Heracles to join the gods on Mount Olympus — and to be placed among the stars — one of the constellations preserved by Claudius Ptolemy.
We’ll have more about Hercules tomorrow.
Script by Damond Benningfield
Most of the “star pictures” in the night sky look nothing like their namesakes. But one beautiful exception lunges across the southwestern sky on May evenings: Leo, the lion. It’s high in the sky at nightfall.
Leo consists of two patterns of stars that the brain puts together to make a lion. A backward question mark represents the head and mane. And a triangle of stars to the lower left forms the lion’s hindquarters and tail.
Leo is best known for its bright stars — especially Regulus, its brilliant heart. But the constellation also contains quite a few bright galaxies. Leading the list are three galaxies that form the Leo Triplet: M65, M66, and NGC 3628.
NGC 3628 is the most interesting of the three. Like our own Milky Way, it’s a spiral — a pinwheel that spans at least a hundred thousand light-years. We see it edge-on, so it looks like a streak of light with lines of dark dust running down the middle.
Close encounters with the other galaxies have pumped up NGC 3628. They’ve triggered the birth of millions of new stars near the galaxy’s core. And they’ve pulled out a tail of gas that spans a quarter of a million light-years — enough gas to make half a billion stars as massive as the Sun. In fact, the tail has given birth to millions of stars already.
The Leo Triplet is just one of the wonders in one of the night sky’s most easily recognizable constellations: the lion.
Script by Damond Benningfield
Over the centuries, no planet has been as frustrating to study as Mercury. The Sun’s closest planet never moves far from the Sun in our sky. So when astronomers pointed telescopes at Mercury, it was almost always screened by twilight and a thick layer of Earth’s atmosphere. So most of what we know about Mercury has come from spacecraft that visited the planet.
You can see the difficulty yourself the next few days. Mercury is quite low in the east not long before sunrise. It’s almost at its farthest point from the Sun, and it looks like a fairly bright star. But at that low altitude, its light has to pass through a thick layer of air, which blurs the view. The glow of twilight makes the view even murkier.
Without the ability to see surface features, it was hard to nail down the length of Mercury’s day. The planet always shows the same face when it’s closest to Earth. So it looked like Mercury was locked so that the same hemisphere always faced the Sun, just as the same side of the Moon always faces Earth.
But that’s not right. Radio telescopes have showed that Mercury makes three turns on its axis for every two orbits around the Sun. That means a “day” on Mercury — the time from one noon to the next — lasts 176 Earth days — long days and nights for the Sun’s closest planet.
Mercury appears near the Moon the next couple of mornings. It’s to the lower left of the Moon tomorrow, and closer to the right on Monday.
Script by Damond Benningfield
The atmosphere of Mars is quite different from Earth’s. It’s colder, thinner, and it’s made mainly of carbon dioxide. In one way, though, the skies of the two planets are similar: both of them have clouds. And for the most part, the clouds themselves are alike as well.
Because Mars is so cold, the clouds are made entirely of ice — frozen water or carbon dioxide. There’s not much water in the Martian atmosphere, so the clouds are thin. And they’re usually much higher than even the highest clouds of Earth.
But Mars also has some clouds that are a bit different from those on Earth. That includes “dots” and some long, skinny ribbons.
An orbiting spacecraft has seen the dots in a specific region of Mars, south of the equator. The clouds are almost perfectly round. They’re up to 60 miles in diameter, a few miles thick, and they top out at altitudes of 30 to 50 miles. Some are seen at dawn, while others are seen in clumps in the dawn or evening twilight. The clouds could form as the atmosphere interacts with some odd spots in the Martian magnetic field.
The elongated clouds are seen in volcanic regions. The longest span about 1500 miles, and are up to a hundred miles wide. They may be sculpted by winds flowing over volcanic peaks — some odd clouds for the Red Planet.
Mars stands close to the lower left of the Moon at dawn tomorrow. The planet Saturn is about the same distance to the upper right of the Moon.
Script by Damond Benningfield
The solar system is pretty settled. The planets appear to be following orbits that have remained stable for billions of years. But in the early days, things might have been a lot more chaotic. According to one model, in fact, the giant planets Jupiter and Saturn might have moved much closer to the Sun before they moved back out again.
The planets probably took shape from a disk of gas and dust around the Sun. Small bits of material stuck together to make bigger bits, all the way up to planets. But much of the material remained free. There was enough of it to exert both a drag and a pull on the giant planets.
In this model, Jupiter — the Sun’s heaviest planet — was born at about two-thirds of its present distance from the Sun. It quickly moved inward, though, all the way to the orbit of Mars. Saturn — the second-most-massive planet — was dragged inward as well. Jupiter and Saturn thinned out the supply of gas and dust and the leftover planetary building blocks — either by scooping them up or kicking them away from the Sun. That changed the gravitational balance of the solar system. Jupiter and Saturn moved outward — settling into their current stable orbits around the Sun.
Saturn is in the dawn sky now, and looks like a bright golden star. Unlike a star, though, it doesn’t twinkle — its light holds steady. Tomorrow, it will stand close to the left of the Moon. The Moon will pass between Saturn and Mars the next morning; more about that tomorrow.
Script by Damond Benningfield
One of the larger moons of the planet Neptune has been through a lot. It might have started as an asteroid, and was captured by Neptune’s gravity. Or it might have started as a moon, but was hurled into a wild orbit when Neptune grabbed its largest moon. And since then, it’s been battered by impacts with other space rocks.
Nereid was discovered 75 years ago today, by Gerard Kuiper. It was only the second moon seen around the giant planet, and it’s the third-largest of Neptune’s 16 known moons.
Kuiper was observing Neptune with the 82-inch telescope at McDonald Observatory. In a pair of 40-minute exposures, the moon showed up as a tiny star near the planet. Kuiper suggested the name Nereid because, in mythology, the Nereids were daughters of Neptune.
We don’t know a lot more about the moon today than when it was discovered. It’s more than 200 miles in diameter, its gray surface probably is coated with ice and rock, and the surface is rough — perhaps the result of billions of years of impacts.
Nereid follows the most lopsided orbit of any good-sized moon in the solar system. It ranges from less than a million miles from Neptune to about six million miles. That suggests that Nereid could be the last of Neptune’s original moons. When Neptune captured its biggest moon, Triton, Triton’s gravity could have kicked out all the others, leaving only Nereid — in a wild orbit around a giant planet.
Script by Damond Benningfield
Earth’s magnetic field sometimes does a flip. The north magnetic pole becomes the south pole, and vice versa. On average, it happens once every few hundred thousand years.
But sometimes, it’s more of a flip flop — the field flips right back over.
One flip-flop took place about 42,000 years ago. Known as the Laschamps Excursion, the flip lasted only a few hundred years. And a recent study said the transition could have been a major problem for Earth’s environment.
The magnetic field protects us from radiation from the Sun and beyond. As the field flips, though, it gets weaker. That allows more radiation to reach the upper atmosphere, where it can zap the ozone layer. In turn, that allows more radiation to reach the surface, where it can cause skin cancers, mutations, and other problems.
During the Laschamps era, the magnetic field dropped to only a few percent of its current strength. Scientists studied the effect of that drop by examining trees buried in New Zealand. The trees’ annual growth rings contained high levels of radioactive carbon — an indication that more radiation was reaching the surface.
The researchers said that the weaker field could have been related to major climate changes, including animal extinctions in Australia.
No other research has reported such dramatic impacts from a flip. So it’s unclear what effect the next flip — or flip-flop — might have on life on our planet.
Script by Damond Benningfield
Earth’s magnetic field is a protective blanket. It keeps charged particles from the Sun and beyond from hitting the surface and much of the atmosphere, where they could cause a lot of problems. But it’s a lumpy blanket. It doesn’t provide the same level of protection for the whole planet. Instead, the magnetic field has peaks and valleys.
Today, there’s a deep “valley” over parts of South America and the South Atlantic Ocean. Known as the South Atlantic Anomaly, it allows particles in Earth’s radiation belts to come closer to the surface than anywhere else.
That’s a big problem for orbiting spacecraft. Some have been damaged when they passed through the anomaly. The International Space Station has extra shielding to keep its crew safe.
About 3,000 years ago, there was a big “peak” in the magnetic field over the Middle East. The field was stronger than usual there, and stayed that way for centuries.
Some of the most recent evidence for it came from bricks from Mesopotamia, around present-day Iraq. The bricks contain bits of iron oxide. When the bricks were fired, the iron particles recorded the condition of the magnetic field at the time. The bricks also contained the seals of kings. Archaeologists know just when the kings ruled. That allowed scientists to piece together the magnetic history of the region — confirming a big “lump” in Earth’s ancient magnetic field.
More about the magnetic field tomorrow.
Script by Damond Benningfield
Be careful what you say — a single phrase can define a legacy.
Consider Frances Baily. He served four terms as president of the Royal Astronomical Society and compiled some of the most important star catalogs in history. But he’s best known for five little words: “like a string of beads.”
Baily was born 250 years ago today, in England. As a young man, he traveled to the wilds of North America, then joined the London Stock Exchange. He was especially good at the mathematical side of things, compiling guides about annuities and life insurance. He made a fortune, then retired in 1825 to spend all of his time on astronomy.
Baily had already helped establish the forerunner of the royal society. He used his skills from his days in business to compile star catalogs — work that required a lot of tedious calculations. One of them was the leading publication of its time.
In 1836, Baily watched a solar eclipse from Scotland. Just before the Sun vanished, he noticed little points of light around the edge of the Moon. Edmond Halley had seen the same thing more than a century earlier. Halley even explained those points: they’re sunlight shining through gaps between lunar mountains and craters.
To his fellow astronomers, Baily described them as “a row of lucid points, like a string of beads.” So today, the points are known as “Baily’s beads” — insuring a bit of immortality for an insurance expert-turned-astronomer.
Script by Damond Benningfield
Russian astronomer Friedrich Wilhelm von Struve discovered and catalogued thousands of binary stars — pairs of stars that are gravitationally bound to each other. But a system that he first saw in 1829 was so striking that he gave it a special name: Pulcherrima — “the most beautiful.” It honors the contrasting colors of the two stars. One looks pale orange, while the other looks blue-white or even green.
The system is also known by an even older name: Izar, “the girdle,” because it represents the middle of Boötes, the herdsman. Regardless of what you call it, most skywatchers agree with Struve: Seen through a telescope, the pair is quite beautiful.
The orange star is a giant. It’s burned through its original hydrogen fuel and is nearing the end of its life. As a result, it’s puffed up to many times the diameter of the Sun. That “puffiness” caused the star’s outer layers to cool, which is why it looks orange.
Its companion is much hotter, so it shines almost pure white. It looks blue or green only when it’s compared to the orange star. It’s less massive than the companion, so it has a lot longer to go before it reaches its own “giant” phase.
Boötes is in the east as night falls. Look for its brightest star, brilliant yellow-orange Arcturus. Izar is the first noticeable star to the left of Arcturus. To the eye alone, it looks like a single point of light. But a telescope reveals the true nature of this colorful duo.
Script by Damond Benningfield
The brightest star in the night sky is getting ready to leave it for a while. Sirius, the Dog Star, is low in the southwest as night falls. Over the next few weeks, it’ll sink deeper into the twilight, then disappear from view.
Sirius is almost nine light-years away. And it actually consists of two stars, not one. The one we see is a good bit bigger, brighter, and heavier than the Sun. The other is about the same mass as the Sun, but a whole lot smaller — only as big as Earth.
That star is a white dwarf. It’s the crushed core of a star that originally was more massive than its companion. Because of those extra pounds, the star aged more quickly. It puffed up to giant proportions. When it could no longer produce energy in its core, it cast off its outer layers, leaving only the dead core. The white dwarf is so small and faint that it’s visible only through a telescope.
The bright star of Sirius eventually will suffer the same fate. And so will the Sun — but not for several billion years.
Sirius will return to view — in the morning sky — in August, with the exact date depending on your location. From ancient Egypt, it disappeared for about 70 days. Sirius was important in both religious and secular life. So 70 days became the length of time set aside to prepare a dead king’s body for the afterlife. And the star’s reappearance marked the start of a new year — in a calendar regulated by the Dog Star.
Script by Damond Benningfield
Stars are huge — anywhere from about 10 times the diameter of Earth to a hundred thousand times or more. Such a scale is just hard to fathom. One way to envision it is to consider how long it would take you to make one turn around such a giant body.
An extreme example is Antares, the bright orange heart of Scorpius. It’s to the lower left of the Moon as they climb into good view tonight, after midnight, and about the same distance to the upper right of the Moon tomorrow night.
Antares is a supergiant — one of the biggest stars in the galaxy. It’s also one of the brightest and heaviest. The exact numbers are a bit uncertain. In part, that’s because its outer layers are extremely thin — they just kind of taper off into space. And Antares is blobby instead of perfectly round. But a good estimate says it’s almost 600 million miles in diameter — about 75 thousand times wider than Earth.
To get a better picture of that, imagine flying around Antares in a passenger jet at 600 miles per hour. At that speed, you could circle the Moon in about 11 hours, and Earth in about 40. And it would take six months to circumnavigate the Sun.
For Antares, though, you’d need to pack a lot of movies on your mobile device. That’s because it would take 350 years to make one full turn around it — a whole bunch of frequent-flier miles for circling around a supergiant star.
Script by Damond Benningfield
Over the millennia, stars acquire a lot of names. Some make sense, some don’t. And some of them might have gotten mixed up along the way.
An example is the fourth-brightest star of Leo, the lion, which is about 58 light-years away. It represents the lion’s hip. A few centuries ago, it was assigned the name “Delta Leonis” — an indication of its ranking within the constellation. But it also has some older names, including Zosma and Duhr.
Zosma comes from ancient Greek. It means “the girdle.” But that may be a mixed-up version of the original word, which meant “hip” or “back” — the star’s correct position in the lion’s anatomy. Duhr comes from ancient Arabic. It’s a shortened version of a phrase that means “the lion’s back.”
Regardless of the name, Zosma is a pretty impressive star. It’s more than twice the size and mass of the Sun, and about 15 times brighter. And its surface is thousands of degrees hotter.
Studies have shown that Zosma could be up to three-quarters of a billion years old. Stars of its mass burn through their nuclear fuel much faster than stars like the Sun. As a result, they live much shorter lives. Zosma should end its “prime-of-life” phase and head into old age in a few hundred million years. It’ll shine hundreds of times brighter than it does now — giving the lion a brilliant hip.
Zosma is high in the sky at nightfall. It’s well to the right of Regulus, the lion’s brightest star.
Script by Damond Benningfield
Immanuel Kant is best known for his ideas about philosophy, from ethics to the nature of knowledge. But he also played a role in the development of an idea about how planets are born. And while many of the details were off, his basic idea was sound.
Kant was born 300 years ago this week, in the German state of Konigsberg. And during his 80 years, he never left it.
He enrolled in the University of Konigsberg at age 16. But his father died, and he was forced to leave the university. He became a tutor for well-to-do families. He was able to return and finish his education in 1755.
Kant was interested in just about everything — including science. Soon after completing his degree, he wrote about earthquakes, the weather, and more. One of his early works was “Universal Natural History and Theory of the Heavens.” In it, he described a “nebular” hypothesis for the formation of planets.
A scientist in Sweden had conceived the idea a couple of decades earlier. Kant developed it further. He wrote that the Sun and planets were born from a nebula — a giant spinning cloud of gas and particles. Gravity caused the cloud to flatten, forming a disk. Material in the disk stuck together to make larger and larger chunks — eventually forming planets.
Today, scientists have worked out more of the details. But the basic idea remains the same — Kant’s hypothesis provides a basic description of how planets are born.
Script by Damond Benningfield
Few constellations have as many backstories as Virgo, the virgin. In ancient Greece and Rome, it was linked with several goddesses, each with her own story.
In one story, she was Dike, the goddess of justice. She lived when the gods known as the Titans ruled the land. Everything was peaceful, it was always spring, and living was easy. But after Zeus and the Olympians defeated the Titans, life got much more complicated. The goddess had to work a lot harder to maintain peace. Eventually, things got so bad that she turned her back on humanity and settled among the stars.
In another story, Virgo was Demeter, the goddess of agriculture and the harvest. The Sun entered that region of the sky in the fall, around the time of the harvest, strengthening the connection.
Virgo’s brightest star is Spica — a name that means “an ear of grain.” It’s the only truly bright star around. It’s about 250 light-years away, and consists of two stars in a tight orbit around each other. The more massive of the two is likely to end its life as a supernova — a titanic blast fit for the early gods of ancient Greece.
Spica stands just a whisker away from the full Moon tonight. They’re low in the southeast as twilight fades, separated by about half a degree — less than the width of a pencil held at arm’s length. They arc low across the south during the night, and set around dawn.
Tomorrow: an early recipe for a system of planets.
Script by Damond Benningfield
If you look straight up as the sky gets dark this evening, you won’t see much of anything. The region that’s high overhead is populated by some especially faint stars and constellations. But there’s a ring of brighter stars around it.
The point directly overhead is called the zenith. And most of the time, unless you’re lying on a blanket and just watching the stars, you’re not likely to pay it much attention. It’s just too uncomfortable to tilt your head back that much. Instead, most of us look at what’s closer to eye level.
Sometimes, it’s worth looking up there. Tonight really isn’t one of those times. The constellations near the zenith at nightfall include Leo Minor, the little lion; Lynx, a constellation so faint that you need the eyes of a cat to see it; and the part of Ursa Major that includes the feet and legs of the great bear, which are faint. And there’s an almost-full Moon in the sky, which overpowers dimmer stars.
But if you look a little below the zenith, the view is more impressive.
High in the south, for example, there’s Regulus, the bright heart of Leo, the big lion. And about the same height in the west, you’ll find Pollux and Castor, the “twin” stars of Gemini.
Finally, in the northeast, you’ll find perhaps the most famous star pattern of all: the Big Dipper. Its stars outline the body and tail of Ursa Major. They’re the easy-to-spot parts of the great bear, standing high in the sky — just not at the zenith.
Script by Damond Benningfield
The Little Dipper is famous for the star at the tip of its handle: Polaris, the North Star. Earth’s axis points in that direction, so all the other stars in the night sky appear to circle around it.
The second-brightest star in the dipper is Kochab, at the lip of the bowl. It isn’t nearly as famous as Polaris, but it’s almost as bright.
Kochab is a giant — more than 40 times the Sun’s diameter, and almost 400 times its brightness. It’s so big because it’s nearing the end of its life. The nuclear reactions deep inside the star push on the surrounding layers of gas, making them puff outward.
Just when a star enters the giant phase of life depends on its mass. Heavier stars age much faster, so they “burn out” more quickly. And Kochab is more massive than the Sun.
But just how massive has been the subject of debate. Studies using different techniques have yielded estimates of about 1.3 to 2.5 times the Sun’s mass. If Kochab had a companion star, it would be easy for scientists to measure the masses of both stars. For solitary stars like Kochab, though, astronomers rely on models of how stars behave. Today, the models seem to indicate a mass of about 2.2 times the Sun’s. But that isn’t completely settled. Until it is, we won’t know the complete story of Kochab.
Kochab is moderately bright, and stands to the right of Polaris at nightfall. It rotates directly above the Pole Star in the wee hours of the morning.
Script by Damond Benningfield
The Lyrid meteor shower is building toward its peak, on Sunday night. The Moon will be almost full then, so its glare will wash out all but the brightest of the “shooting stars.”
The shower is the offspring of Comet Thatcher 1861. The comet orbits the Sun once every 415 years or so.
As Thatcher approaches the Sun, some of the ice at its surface vaporizes. That releases small bits of dirt and rock into space. This debris spreads out along the comet’s path. Earth flies through this path every April. Some of the comet dust slams into our atmosphere and burns up — forming meteors.
At least, most of it does. It’s likely that some of the grains fall to the surface. In fact, a recent study might have found some of those grains at the bottom of New York’s Hudson River.
Researchers sifted through layers of sand and mud deposited thousands of years ago. The layers included fossils of microscopic organisms that were coated with tin — an element that likely came from outside Earth. The scientists also found other elements that probably originated outside our planet as well. The layers were laid down at roughly 400-year intervals — suggesting a possible connection with Comet Thatcher and the Lyrid meteors.
The findings are preliminary. So we don’t know for sure whether there’s a link between the sediments at the bottom of the Hudson River and the streaks of light in April’s night skies.
Script by Damond Benningfield
The Small Magellanic Cloud is a satellite galaxy of the Milky Way. It’s about 200,000 light-years away, it contains hundreds of millions of stars, and it’s easily visible to the eye alone — from the southern hemisphere. And it may actually consist of two separate but related halves — two galaxies for the price of one.
Astronomers had suggested that possibility almost four decades ago. And a recent study provided the best evidence yet to support the idea. It found two large star-forming regions that are separated by about 15,000 light-years. One lines up in front of the other, making it hard to see them as individual objects.
A team studied the galaxy in several ways. It found that gas and dust are split into two distinct regions. Their material moves in different ways, and has a different composition.
The researchers also studied hot, young, bright stars. That also revealed two separate regions. And like the gas, the stars in the regions move in different ways, and have a slightly different makeup.
The team said the two regions could be remnants of two galaxies that came together long ago. On the other hand, the region that’s closer to us could be the main body of the galaxy. The region behind it then could be a tail of stars and gas pulled out by the gravity of the nearby Large Magellanic Cloud, which is bigger and heavier.
Either way, this close companion to the Milky Way may be more than meets the eye.
Script by Damond Benningfield
The heart of the lion stays close to the Moon the next couple of nights. The bright star that marks the lion’s heart is Regulus. It’s to the lower left of the Moon at nightfall this evening, and to the upper right of the Moon tomorrow evening.
Regulus is impressive. It’s a system of four stars, but only one shines bright enough to see. Known as Regulus A, it’s almost four times the Sun’s mass, and more than 300 times the Sun’s brightness.
But the Moon is even closer to another star of Leo that’s more impressive. Eta Leonis is to the upper left of Regulus. It looks fainter than Regulus. Under the glare of the nearby Moon, in fact, it can be hard to see — especially from light-polluted cities.
That’s only because Eta Leonis is much farther than Regulus — about 1800 light-years, versus only 79 light-years for Regulus.
In fact, Eta Leonis is a one-percenter — among the biggest and brightest stars in the galaxy. Studies show that it’s about 10 times heavier than the Sun, about 50 times wider, and about 20 thousand times brighter.
Eta Leonis is only about 25 million years old, compared to four and a half billion years for the Sun. But thanks to its great mass, the star is near the end of its life. Within a few million years, it’s likely to explode as a supernova. For a while, it will greatly outshine every other star in the galaxy — a brilliant beacon for the lion.
Script by Damond Benningfield