StarDate

People collect all kinds of things, from baseball cards to Persian rugs. Over the past 40 years, some NASA aircraft have collected dust – grains of dust from beyond Earth. Many of the collection efforts have taken place during meteor showers. That’s included the Geminid shower, which is at its peak tonight.

A meteor shower takes place when Earth flies through a trail of particles that were shed by a comet or asteroid. Many of the particles burn up in the upper atmosphere, creating the streaks of light known as meteors.

But many more grains are too...

A couple of thousand years ago, a large asteroid or comet might have been blasted apart. And we’re still seeing the fireworks from its destruction – as the Geminid meteor shower, which will reach its peak tomorrow night.

Most meteor showers flare to life when Earth passes through the orbital path of a comet. The comet sheds bits of rock and dirt, which spread out along its orbit. As Earth flies through this trail of debris, the solid grains ram into the atmosphere, forming the glowing streaks known as meteors.

But the Geminids are a bit...

The Sun isn’t easy to influence. It’s more than a thousand times the mass of Jupiter, the solar system’s largest planet, and more than 330,000 times the mass of Earth. Even so, a recent study says the planets might influence our star’s magnetic cycle – perhaps making conditions more comfortable for life.

The Sun goes through many cycles of magnetic activity. The best known lasts an average of 11 years. At the cycle’s peak, the Sun is much more active than average. It pelts Earth and the other planets with higher levels of radiation and charged part...

Storms on the Sun can cause all kinds of problems. They can knock out satellites and black out power grids. They can interfere with GPS and disrupt some radio broadcasts. They can even have an impact on human health.

Solar storms happen when the Sun’s magnetic field gets tangled up. Lines of magnetic force can snap, then reconnect. That produces outbursts of radiation and charged particles. When the particles hit Earth, they’re funneled toward the surface by our planet’s own magnetic field. And that’s what causes the problems.

Among the health concerns...

The Moon and the heart of the lion just miss each other tonight – at least as seen from the United States. As they climb into good view, after midnight, the Moon and the star Regulus will be separated by just a skosh. The farther north and east your location, the closer together they’ll appear. From some spots, they’ll be almost touching.

And from much of Canada across to northern Norway they will touch – the Moon will occult the star. It’ll pass directly in front of Regulus, blocking it from view.

The Moon can occult...

A couple of years ago, a space telescope discovered something odd about NGC 6505. The galaxy is encircled by a ring. It isn’t part of the galaxy itself. Instead, it’s an image of a background galaxy – one that’s billions of light-years farther.

Einstein Rings are named for Albert Einstein because they were predicted by his theory of gravity. The gravity of a foreground object acts as a lens – it bends and magnifies the light of a background object.

On small scales, gravitational lenses have revealed everything from black holes to rogue planets. Galaxies are much b...

The Moon is a “dead” world. It trembles with a few small moonquakes, and there may be occasional “burps” of gas. But for the most part, not much happens inside it.

That’s definitely not the case for one of the moons of the giant planet Jupiter. Io is the most volcanically active world in the solar system. It’s covered by hundreds of volcanoes and pools of hot lava. Some of the volcanoes are larger than anything on Earth, and the lava is much hotter. The volcanoes can send gas and ash hundreds of miles high. Some of this...

The Moon forms a beautiful grouping with the planet Jupiter and the twins of Gemini tonight. Jupiter looks like a brilliant star. It’s below the Moon as they climb into view, by about 8:30. Castor, the fainter of Gemini’s twins, is to the left of the Moon. And Pollux, the brighter twin, is to the lower left. The grouping is even tighter at first light tomorrow.

The Moon circles through Gemini roughly once a month – the time it takes to complete one full turn through the background of stars. If you made a movie of those passag...

For radio astronomers, there’s some good news and some bad news. On the good side, a pilot project with SpaceX has devised a way to reduce the radio interference produced by satellites. On the bad side, the satellites can produce accidental interference.

Radio telescopes tell us things about the universe that we can’t get any other way. But the telescopes are extremely sensitive. Transmissions from an orbiting satellite are like bright headlights – they overpower the subtle signals of astronomical objects. There are more than 15,000 satellites in orbit today – a five-fold increase in just six years. And the...

Most of the stars are so small and far away that they’re nothing more than pinpoints even in the largest telescopes. That makes it impossible to measure the size of a star. But astronomers can measure the sizes of some stars – not with a giant telescope, but with a collection of smaller ones.

The technique is called interferometry. It links up several telescopes. The combo provides an especially sharp view of the heavens. If the telescopes are, say, 300 feet apart, then the combined view is as clear as that of a single telescope 300 feet in diameter. The...

[3, 2, 1, ignition, and liftoff of SOHO and the Atlas vehicle on an international mission of solar physics.]

Generally speaking, staring at the Sun non-stop for decades is a bad idea. But a spacecraft launched 30 years ago this week has done just that. It’s told us about the Sun’s interior, its surface, and its extended outer atmosphere. That’s helped scientists develop better forecasts of space weather – interactions between Sun and Earth that can have a big effect on our technology.

The craft is called SOHO – Solar and Heliospheric Observatory. It was launched into an orbit arou...

Scientists have been searching for dark matter for decades. They haven’t found it – every experiment they’ve devised has come up empty. But they haven’t given up. Among other ideas, they’re thinking about ways to use moons, planets, and stars as detectors.

Dark matter appears to make up about 85 percent of all the matter in the universe. We know it’s there because its gravity pulls on the visible stars and galaxies around it.

Dark matter may consist of a type of particle that almost never interacts with normal matter. But it should inter...

Things are heating up for a planet that orbits the brightest star of Aries. The star is expanding to become a giant, so it’s pumping more energy into space. That will make temperatures extremely uncomfortable on the planet.

Hamal is at the end of its life. It’s converted the hydrogen in its core to helium. Now, it’s getting ready to fuse the helium to make other elements. That’s made the core hotter. And that’s caused the star’s outer layers to puff up – to more than a dozen times the diameter of the Sun. So Ha...

As most parents can tell you, coming up with names isn’t easy. It sometimes takes a while to settle on something that sounds just right. It wasn’t easy for the people who named the constellations, either. Some of the names sound like they just gave up. They picked a region of the sky with few stars, gave it the name of a nearby bright constellation, then added the word “minor.”

All three of these minor constellations are in good view at dawn: Ursa Minor, Canis Minor, and Leo Minor.

The most famous of the bunc...

The shortest season on the planet Mars begins today – autumn in the northern hemisphere, and spring in the southern hemisphere. It will last for 142 Mars days – almost eight weeks less than the longest season.

Mars has seasons for the same reason that Earth does – it’s tilted on its axis. And the tilt is at almost the same angle as Earth’s.

But the seasons on Mars are more exaggerated because the planet’s orbit is more lopsided. A planet moves fastest when it’s closest to the Sun, and slowest when it’s farthest from the Sun. Th...

The Moon slides by Saturn the next couple of nights. The planet looks like a bright star. It’s to the left of the Moon as night falls this evening, and to the lower right of the Moon tomorrow night.

Saturn is best known for its rings. They’re almost wide enough to span the distance from Earth to the Moon. Right now, we’re viewing them almost edge-on, so they look like a thin line across the planet’s disk.

Saturn isn’t the only world with rings. The solar system’s three other giant outer...

Planets are tough little buggers. They can form and survive in some extreme environments. In fact, the first confirmed planets outside our own solar system orbit the remnant of a dead star – a pulsar.

A pulsar is tiny – the size of a small city. But it’s more massive than the Sun. A teaspoon of its matter would weigh as much as a mountain. Yet a pulsar spins rapidly – up to several hundred times per second. It has an extreme magnetic field. The field shoots “jets” of particles out into space. As the pulsar spins, the jets can sweep ac...

[pulsar audio]

This is the rhythm of the stars – the beat of dead stars. It’s the “pulses” of radio waves produced by rapidly spinning stellar corpses. They produce beams of energy that sweep around like the beacon of a lighthouse. Radio telescopes detect the beams when they sweep across Earth.

The stars are known as pulsars. They’re some of the most extreme objects in the universe. They’re neutron stars – the dead cores of some of the most massive stars. When a heavy star can no longer produce nuclear reactions in its core, the core colla...

Getting too close to a black hole is bad news. The black hole’s gravity can pull apart anything that’s falling into it atom by atom. A magnetar can do the same thing. And it’s not just its gravity you have to worry about. Its magnetic field can do the job as well – from hundreds of miles away.

A magnetar is a neutron star -the crushed corpse of a once mighty star. It’s heavier than the Sun, but only a little bigger than Washington, D.C. It’s born when a massive star can no longer pr...

When the most massive stars die, they can leave behind two types of corpse. The heaviest ones probably form black holes. But the fate of the others is no less exotic. They form neutron stars – ultra-dense balls that are more massive than the Sun, but no bigger than a small city.

A massive star “dies” when its core can no longer produce nuclear reactions. For a star of about eight to 20 or more times the mass of the Sun, the core collapses, while the star’s outer layers explode as a supernova.

The gravity of the coll...

You can always count on the constellations. Over the course of a human lifetime, their configuration doesn’t change – they don’t appear to move at all.

That’s an illusion, though. The stars are all so far away that we don’t see any motion. But they’re all moving in a hurry. And one of the fastest is in view on autumn evenings.

Gamma Piscium is the second-brightest member of Pisces, the fishes. The constellation stretches across the east and southeast at nightfall. Gamma Piscium is near its top right corner – part of a pentagon of...

An interloper from another galaxy scoots low across the south on October evenings. It’s a tight family of stars – hundreds of thousands of them. The stars probably belonged to another galaxy that was consumed by the Milky Way in the distant past.

Messier 30 is low in the south at nightfall, in Capricornus. The sea-goat’s brightest stars form a wide triangle. M30 is on the lower left side of the triangle

Messier 30 is a globular cluster – a ball of stars about 90 light-years wide. Most of the stars are concentrated in the cluster’s dense core. The...

If you’ve ever left a can of soda in the freezer for too long, you can appreciate what happened to the largest moon of the planet Uranus: It cracked.

Titania is almost a thousand miles in diameter – less than half the size of our moon. But it orbits Uranus at about the same distance as the Moon does from Earth. And like the Moon, it’s locked in such a way that the same hemisphere always faces its planet.

When Titania was born, its interior was warm. But it quickly froze. As it did so, th...

The planet Uranus has always been an oddball. It lies on its side, so it rolls around the Sun like a giant bowling ball. Its magnetic field is tilted and offset more than any other planet’s.

And for the past four decades, it’s seemed that the planet radiated less energy into space than it receives from the Sun. The solar system’s other giant planets all radiate at least twice as much energy as they receive – mainly in the form of heat left over from their formation.

But two recent studies have changed that sto...

If you suffer from seasonal affective disorder during the dark winter months, then stay away from the poles of Uranus. The giant planet is tilted on its side. So during each 84-year-long orbit around the Sun, the polar regions have 42 years of daylight followed by 42 years of darkness – a looong time to feel sad.

Planetary scientists have been watching the slow change of seasons for two decades with Hubble Space Telescope. At visible wavelengths, Uranus looks like an almost-featureless ball – faint bands of clouds are about the only details. A smattering of methane in the atmosphere absorbs red...

Uranus is the seventh planet of the solar system, so it’s a long way from both the Sun and Earth. Right now, it’s about 1.7 billion miles away. At that distance, under especially dark skies it’s barely bright enough to see with the eye alone. It’s easy to pick out with binoculars, though.

This is an especially good week to look for the planet because it reaches opposition, when it lines up opposite the Sun. It rises around sunset and is in view all night. And it shines brightest for the entire year. In early ev...

A barely-there crescent Moon teams up with the disappearing “morning star” in tomorrow’s dawn twilight. But there’s not much time to look for them.

The Moon will cross between Earth and the Sun in a couple of days. It’ll be lost in the Sun’s glare. It will return to view, in the evening sky, by Friday or Saturday.

Venus is getting ready to disappear in the dawn twilight as well. It will cross behind the Sun on January 6th. It’s a slower passage, so the planet will be hidden in the Sun’s glar...

If you ever warp over to another star, it would help to know its distance. Say, for example, you wanted to visit Spica, the brightest star of Virgo, which is quite close to the Moon at dawn tomorrow. The system is worth visiting because it consists of two giant stars. They’re so close together that their shapes are distorted, so they look like eggs.

The best measurement we have says that Spica is 250 light-years away. But there’s a margin of error of about `four percent. So you could undershoot or overshoot the system by 10 light-years.

The patchiest of all meteor showers will be at its best tomorrow night. Unfortunately, this is one of its off years. At best, it might produce a dozen or so “shooting stars” per hour.

Over the past two centuries, though, the Leonids have produced some amazing outbursts. The first of these came in 1833. Skywatchers in parts of America reported rates of a hundred thousand meteors per hour – not a shower, but a storm. The nature of meteor showers was unknown at the time, so many saw the outburst as the end of the world.

The Leonid...

Galaxies frequently collide with each other, and the results can be spectacular. The encounters can pull out giant ribbons of stars. They can trigger intense bouts of starbirth. And they can scramble a galaxy’s stars and gas clouds, creating beautiful rings that look like cosmic bulls-eyes.

One well-known galaxy that’s experienced a head-on collision is the Cartwheel. It’s about 500 million light-years away, in the constellation Sculptor, which is low in the south on November evenings.

The Cartwheel is a good bit bigger than the Milky Way. It has a bright inner ring of mai...

Nicolas-Louis de Lacaille had a great imagination. In the 1750s, the French astronomer mapped more than 10,000 stars from the southern tip of Africa. Lacaille used those stars to create 14 new constellations.

One of them is Sculptor. Lacaille originally called it the Sculptor’s Studio. It depicted a carved head atop a stool, plus a hammer and chisel and a block of granite.

But all of that takes a lot of imagination to see. All of the constellation’s stars are so faint that Sculptor is invisible from light-polluted cities and suburbs.

Sculptor is impo...

The brightness of any star that’s in the prime phase of life is controlled by the star’s mass: Heavy stars are brighter than lightweight stars. But it’s not a simple one-to-one kind of relationship. A star that’s twice the mass of the Sun isn’t twice as bright – it’s more than 15 times as bright.

That’s because gravity squeezes the core of a heavier star more tightly. That increases the core’s temperature, which revs up the rate of nuclear reactions. That produces more energy, which makes its way to the surface and shines out int...

Edwin Hubble gets the credit for discovering that the universe is expanding. But that finding was made possible by work done by Vesto Slipher. He was the first to measure the motions of distant galaxies – the key to Hubble’s discovery.

Slipher was born 150 years ago today, in Mulberry, Indiana. He worked on the family farm, and developed an interest in astronomy. A college professor helped him get a job as an assistant at Lowell Observatory in Arizona, where he worked for the next five decades.

Slipher studied what were called “spiral nebulae.” It wasn’t certain...

There’s nothing in the night sky quite like the Pleiades. The star cluster forms a tiny dipper. Depending on sky conditions and the viewer’s eyesight, anywhere from a half dozen to a dozen stars or more are visible to the naked eye.

Its unique visage has made the Pleiades one of the most important sky objects in many cultures. The people of the Andes timed the start of the harvest season to its first appearance in the dawn sky. The Aztec year began at about the same time.

In Hawaii, the Pleiades was know...

The Moon shoots the gap between some bright companions tonight: the planet Jupiter and the star Pollux, the brighter “twin” of Gemini. They climb into good view by about 10:30 or 11, and stand high overhead at dawn tomorrow.

Jupiter is the largest planet in the solar system, and it has the most turbulent atmosphere. Hurricane-like storms as big as continents twirl across it.

Thunderstorms can produce lightning bolts far more powerful than any on Earth, as recorded by a passing spacecraft. And the storms might produce their own giant hailstones: “mushballs” as big as softballs.

The id...

In the early 20th century, scientists discovered a mysterious new type of radiation. The higher they went, the stronger it became. They realized that it came from beyond Earth. And 100 years ago tomorrow, it got a name: cosmic rays.

Nobel Prize winner Robert Millikan had become fascinated by the rays from outer space in the early ’20s. He coined the name “cosmic rays” in a paper about them, which he presented to a meeting on November 9th, 1925.

Millikan thought the rays were a form of energy produced by matter that was being born in the space...

Nothing can survive the brutal conditions on the surface of the Moon. But a story that debuted 125 years ago depicted a vast civilization below the surface – a society of insects.

First Men in the Moon was written by H.G. Wells. It was published over several months in two magazines – “The Cosmopolitan” in the United States, and “The Strand” in Britain. The first installment appeared in November of 1900.

In the story, a man named Bedford befriends a scientist named Cavor who’s invented “cavorite” – a substance that nullifies gravity. He builds a ship and covers it with shutters tha...

The black hole at the heart of the Milky Way is like the monster lurking under your bed. It’s four million times the mass of the Sun, and about 15 million miles across – just waiting to gobble up anything that gets too close.

But compared to the black holes in many other galaxies, the one in the Milky Way is less like a monster and more like a dust bunny. The largest ones yet seen are thousands of times bigger. They’re known as ultra-massive black holes. Informally, they’re also called SLABs – stupendously large black holes.

Just...

The Taurid meteor shower has a double identity. It’s split into two different streams, which peak a few nights apart in early November. Neither stream is particularly impressive, but things pick up when they overlap.

Their story begins thousands of years ago, with the breakup of a big ball of ice and dust – Comet Encke. The biggest remaining chunk kept that name. But the breakup created several other big pieces, plus clouds of dust. The whole messy bunch is known as the Encke Complex.

The southern Taurid stream consists of small bits of dust and...

AUDIO: We have contact. We have initial contact – initial contact of the Soyuz capsule with the Expedition 1 crew to the International Space Station.

A key milestone in the human exploration of space took place 25 years ago tomorrow. The first permanent crew took up residence in the International Space Station. And people have been living on the station ever since.

They weren’t the first to actually visit the station. Several groups of astronauts and cosmonauts had spent time assembling the early pieces of the station. And by November 2000, it was ready for full-time occupancy.

Th...

Like other buildings, observatory domes can outlive their usefulness. They may not be big enough for the latest telescopes. The light from encroaching cities can make it hard for them to see the heavens. Or time may just catch up to them.

Many domes and related buildings have been torn down. Others have been converted into offices or libraries. And still others have been abandoned – left to the elements and the ravages of time.

Several of these buildings are scattered around the country – in places like Illinois and the woods of Michigan, for example. Their wall...

The night sky is filled with monsters. And none are more fearsome than the Gorgons – three sisters who were so hideous that a single glance at them turned the observer to stone. One of them was beheaded by Perseus the hero. His constellation shows him holding the head, which is outlined by four stars – the Gorgons.

In mythology, two of the sisters were immortal. But the third, Medusa, was not. Perseus managed to lop off her head with the help of the gods. They gave him an invisibility cloak, a diamond sword, and a bronze shield. He coul...

A young “cotton-candy” planet is hastening its own demise. As it dips close to its star, it appears to trigger giant explosions that erode the planet’s atmosphere.

The planet orbits HIP 67522, a star roughly 400 light-years from Earth. The star is a little bigger and heavier than the Sun, but less than one percent the Sun’s age. Such young stars generate strong magnetic fields. Lines of magnetic force tangle and snap, producing powerful flares. The planet, HIP 67522 b, orbits just a few million miles from the star, so it already receives hefty doses of radiation and charged...

A visitor from far beyond the solar system is getting better acquainted with the Sun this week. Tomorrow, it’ll make its closest approach to the Sun – just 126 million miles. After that, it’ll head back toward interstellar space.

The visitor is 3I/ATLAS. It was discovered on July 1st by an automated telescope that looks for comets and asteroids. Calculations of its orbit quickly showed that it came from outside the solar system. That makes it the third known visitor from interstellar space.

It originated in the galaxy’s “thick disk.” That’s a region that sa...

Big “wobbles” in Earth’s magnetic field more than 40,000 years ago could have made the cultures of the time feel wobbly as well. Early modern humans might have adapted to the wobbly field better than Neanderthals.

Earth’s magnetic field protects the surface from high levels of solar radiation. But during a period known as the Laschamp Excursion, which began 42,000 years ago, the field weakened to just 10 percent of its current intensity. And instead of acting like a bar magnet, with strong north and south poles, it generated smaller poles all across the planet.

As the fiel...

As seen from most of the United States, the Big Dipper is plunging toward the northern horizon as night falls, as if it’s about to dip into a pail of water.

If you line up the stars at the outer edge of the dipper’s bowl, and follow that line to the upper right, the first moderately bright star you come to is Polaris, the Pole Star or North Star. Earth’s north pole aims toward it, so Polaris forms the hub of the northern sky – all the other stars appear to rotate around it. And it’s alw...

The Blue Danube has been performed for some pretty lofty audiences – kings and queens, emperors and empresses, presidents and prime ministers. But a performance earlier this year topped them all: it was aimed at the stars.

The waltz was composed by Johann Strauss II, who was born 200 years ago today. His birthday was one of the motivations for the performance. The other was the 50th anniversary of ESA – the European Space Agency. So the broadcast was mostly symbolic – not a real attempt to contact other civilizations.

The waltz was performed by the Vienna Symphony Orchestra in lat...

A giant companion to a giant star faces an uncertain fate. The star is dying. As it expires, it will blast the companion, drag it inward, zap it with radiation, then loosen its grip on whatever remains.

Mirach is the second-brightest star of Andromeda. It’s passed through the prime phase of life, and now is in the red-giant phase. It’s puffed up to about 85 times the diameter of the Sun, making it shine about 1700 times brighter than the Sun.

Two years ago, astronomers discovered that Mirach has a companion. It’s probably a “failed s...

The black hole at the heart of a distant quasar has the biggest appetite astronomers have ever seen. It gobbles down the equivalent of one Sun per day – more than any other known black hole. It’s fed by the widest disk of gas and dust yet seen. And it outshines everything else in the known universe – 500 trillion times the Sun’s brightness.

The quasar is so far away that we see it as it looked when the universe was a little more than one-tenth of its current age. It was discovered in the early 1980s, but astronom...

We got our first picture from the surface of another planet 50 years ago today, when the Soviet Union’s Venera 9 landed on Venus. It transmitted data from the surface for 53 minutes, including a wide panorama.

Venus is completely covered by thick clouds, so we can’t see its surface from Earth, or even from orbit around Venus – orbiters use radar to peer through the clouds. Venus also has a hot, dense atmosphere, so landing there is tough.

Venera 9 parachuted through the clouds, measuring their thickness and composition. At the surface, it measured the density of the at...

An embryonic star may be about to vanish – perhaps for a century. It’s not going anywhere. Instead, it’ll be cloaked by a dense cloud that encircles two companions.

T Tauri is the prototype for a class of proto-stars. The gravity of such a star is causing it to collapse, making it hot and bright. But its core isn’t hot enough to ignite the fires of nuclear fusion, so it’s not yet a true star.

The star we see as T Tauri is about twice as massive as the Sun. It’s encircled by...

The bull is charging into the evening sky. Taurus is in full view by about 11 o’clock, low in the east. He stands high in the south before dawn. He’s rising earlier each night, and will be in view all night long by about Thanksgiving.

All the stars rise four minutes earlier each night – a result of Earth’s motion around the Sun. Earth makes one full turn on its axis against the background of distant stars every 23 hours and 56 minutes. So, if you looked at the sky every 23 hours and 56 minutes, and you could see through...

The Moon is full tonight, and it’s especially bright as well. And to top things off, it’s the most famous full Moon of them all – the Harvest Moon.

Harvest Moon is the full Moon closest to the fall equinox, so most years it falls in September. But once every five years or so it skips into October. This year, September’s full Moon came 15 days and 10 minutes before the equinox, which took place on the 22nd. This month’s full Moon comes 14 days, 9 hours, 29 minutes after the equinox, so it barely takes Harvest Moon honors.

The...

It’s pretty easy to measure the length of a day on Mars or most other solid bodies. Just pick a feature on the surface and see how long it takes to spin back into view.

It’s not so easy for planets that don’t have a solid surface. We can track bands of clouds, but different bands can move at different speeds.

That’s been an especially tough problem for Saturn, the second-largest planet in the solar system. Scientists have been trying to pin down its rotation rate – the length of its day – for centurie...

Saturn and Venus bracket the pre-dawn sky now. As Saturn drops from view in the west, Venus nudges into view in the east. Saturn looks like a bright star, while Venus is the brilliant morning star.

The planets are both sliding eastward against the background of distant stars.

Saturn lined up opposite the Sun a couple of weeks ago. For a few months around that point, the planet looks like it’s “backing up” against the background of stars – a result of the relative motions of Saturn and Earth.

Earth is closer to the Sun...

Scientists don’t know what dark matter is. But they have some ideas of what it isn’t. And they took a big step in ruling out some possibilities with the release of a study last year.

Dark matter produces no energy – the reason it’s described as “dark.” But we know it’s there because its gravity pulls on the visible matter around it. In fact, it appears to make up about 85 percent of all the matter in the universe.

The leading idea says dark matter consists of some kind of subatomic particle. A top candidate...

At first glance, the dwarf planet Ceres doesn’t seem like a friendly home for life. It’s small, dark, and scarred by impact craters. Yet a deeper look presents a more optimistic picture. It has more water than any body in the inner solar system besides Earth. It has an abundance of organic compounds – the chemical building blocks of life. And it should be warm enough below the surface to sustain microscopic life.

Ceres is the largest member of the asteroid belt – a wide band of debris between the orbits of Mars and Jupiter. It’s about a qu...

The constellations are well armed. Several of the star patterns that depict people or gods are carrying weapons. And some of them are in good view at this time of year.

As darkness falls, look low in the west for the brilliant star Arcturus. It stands at the base of Boštes the herdsman. Like many of the ancient star figures,

Boštes has different stories, and is drawn in different ways. In most depictions, he’s holding something long and straight against his right side. In some cases, it’s a staff. But in others...

The star Fomalhaut is a bit of a disappointment. Almost two decades ago, astronomers announced the discovery of a giant planet orbiting the star – the first exoplanet actually seen at visible wavelengths of light. Almost from the beginning, though, other astronomers questioned the discovery. And they were right. It wasn’t a planet at all, but a big clump of dust – the aftermath of a giant collision.

Fomalhaut is about twice as big and heavy as the Sun, and quite a bit brighter. It’s encircled by wide bands of dust. Most of the dust is at least a...

The southern evening sky is pretty bare at this time of year – lots of dark, empty spaces, but few bright stars. The one notable exception is Fomalhaut. It’s the brightest star of Piscis Austrinus, the southern fish. It’s low in the southeast at nightfall, and arcs across the south later on.

The star we see as Fomalhaut is 25 light-years away. It’s about twice as big and heavy as the Sun, and more than 15 times brighter. It’s young – about 10 percent the age of the Sun. And it’s encircled by wide bands of dust, which may cont...

The Andromeda Galaxy, M31, is encircled by dozens of satellites – smaller galaxies in orbit around it. One of the larger satellites is something of an oddball. Of the three-dozen brightest, it’s the only one that lines up on the far side of Andromeda as seen from our home galaxy, the Milky Way.

M31 is the closest giant galaxy to the Milky Way – just two-and-a-half million light-years away. Messier 110 is a couple of hundred thousand light-years farther. It’s a few thousand light-years in diameter, and contains about 10 billion stars – a tiny fraction the size of Andromeda.

Astr...

Earth has only one moon – one large natural satellite. But it might travel with an entourage of Moon chips – bits of the Moon blasted into space by impacts with asteroids. Some of the chips may share Earth’s orbit around the Sun. Others become “quasi”-moons. They weave around the Sun in a way that looks like they’re orbiting Earth.

Astronomers have catalogued a dozen or more quasi-moons in recent years. The smallest is the size of a house. The largest is about three miles across.

A recent study looked at how easy it would be to...

Neptune is one of the giants of the solar system. But it’s so far away that it’s tough to study. We know little about its interior. And much of what scientists think they know comes from lab experiments and computer models.

Neptune is the Sun’s most remote major planet. So although it’s almost four times Earth’s diameter, it’s a tiny target for telescopes. And only one spacecraft has ever visited the planet – Voyager 2, in 1989.

From those observations, along with those from telescopes on the ground and in space, scientists have developed...

Earth “falls” into a new season today – astronomically speaking. It’s the September equinox, when the Sun crosses the equator from north to south. It marks the start of autumn in the northern hemisphere, and spring in the southern hemisphere.

On the equinoxes, neither the north pole nor the south pole tips toward the Sun, so night and day are roughly the same length in both hemispheres – about 12 hours between sunrise and sunset.

We say “roughly” because there are a couple of caveats.

One is the way we calculate the times of sunrise and sunset. Fo...

Officially, Saturn has 274 known moons. Un-officially, it has billions upon billions of them – the bits of ice and rock that make up the planet’s rings. They range from the size of dust grains to giant boulders. All of them orbit the giant planet like tiny moons.

The system consists of three main bands, which are easy to see. Together, they span about three-quarters of the distance between Earth and the Moon. But there are some thinner, fainter bands as well. One is closer to Saturn than the main bands, while the others are farther.

Desp...

Happy Saturn’s Day – the day of the week named for Saturn, the second-largest planet in the solar system. And the name is especially fitting today, because the planet is at its best for the entire year. It looks like a bright star, shining all night long.

The seven-day week was created in ancient Babylon. The days were named for the seven known “planets.” The list included the Sun, Moon, and the five true planets that are easily visible to the naked eye.

The day was split into 24 hours, with each hour named for a planet...

These are the sounds of Mars: a dust devil … a rover trundling across the surface … the steady sigh of the wind.

All of these sounds were recorded by the Perseverance rover – the first craft to carry microphones to Mars. Scientists have used the recordings to learn more about how sound carries on Mars.

The planet’s atmosphere is less than one percent as thick as Earth’s atmosphere, so it’s much quieter on Mars. It’s especially quiet around noon, when sound waves are bent upward, away from the ground. The atmosphere is also much colder th...

There’s an extraordinary conjunction in tomorrow’s early morning sky – a tight grouping of the Moon, the planet Venus, and the star Regulus. They’re quite low at first light, so you may need a clear horizon to spot them. Venus is the brilliant “morning star,” just a fraction of a degree from the Moon. Regulus is a bit farther from the Moon. It’s much fainter than Venus, but its proximity to the brighter bodies will make it pretty easy to pick out.

This beautiful meeting is possible because all three bodies lie near the ecliptic – the...

A third of a century ago, we knew of only two solar-system bodies beyond the orbit of Neptune: Pluto and its largest moon. Today, the known population of such bodies is in the thousands. And quite a few of them are in the same class as Pluto itself: dwarf planets.

One of the newest members of that class is 2017 OF201. It was discovered in 2017. A recent study found that it may be about a third the size of Pluto. If so, then it most likely would qualify as a dwarf planet.

The object follows a...

The roster of “dwarf planets” keeps growing. But it’s not official – there’s no league office to tell us who’s on the roster and who’s not. Various groups keep their own lists, but they don’t agree on which objects belong.

The dwarf-planet category was formalized a couple of decades ago. Astronomers had discovered some new Pluto-like objects beyond the orbit of Neptune. They had to decide whether to add those objects to the roster of planets, or to put them in a new category. So in 2006, the International Astronomical Union voted to create the “dwarf plane...

A bright star and planet team up with the Moon early tomorrow to form a tight, beautiful triangle. Pollux will stand close to the lower left of the Moon, with much brighter Jupiter about the same distance to the lower right of the Moon. Pollux is the brightest star of Gemini, while Jupiter is a planet.

Jupiter is by far the giant of the solar system. It’s more than twice as massive as all the other planets combined. And it’s about 11 times the diameter of Earth. That makes it big enough to hold 1300 Earths.

Bu...

A star that may be in a death spiral wants the universe to know about it. Every four and a half days it creates a burst of X-rays. The cause of those outbursts may be leading to the star’s demise.

The possibly dying star is in a galaxy that’s about 300 million light-years away. During evening twilight now, that spot is quite low in the west, below the bright star Arcturus.

According to a recent study, the story probably involves the star; a black hole, nicknamed Ansky, that’s a million times the mass of the...

There’s a season for everything, from football to Broadway to allergies. There are seasons in the heavens as well. And the next act in one of those seasons plays out early tomorrow: an occultation by the Moon of the star Elnath – the tip of one of the horns of Taurus.

An occultation takes place when one object covers up another. The Moon occults a few fairly bright stars every month. And the occultations occur in seasons.

That’s because the Moon’s orbit is tilted with respect to the ecliptic – the Sun’s path across the s...

The Milky Way is packed with star clusters – thousands of them. They contain anywhere from a few dozen stars to more than a million. And the most impressive of them all is right in the middle – it surrounds the supermassive black hole at the heart of the galaxy.

The Nuclear Star Cluster contains up to 10 million stars. They extend a couple of dozen light-years from the black hole in every direction. But most of them are packed in close. If our part of the galaxy were that densely settled, we’d have a million stars closer to us tha...

Guillaume Le Gentil spent more than 11 years away from his native France just to witness two brief astronomical events. Along the way, he had to survive war, a hurricane, disease, and grumpy officials. When he got home, he’d lost his job and been declared dead. But the real hardship? He missed both events.

Le Gentil was born 300 years ago this week. He studied theology, but decided on astronomy as a career. He became a member of the Royal Academy of Science at age 28.

Le Gentil and other astronomers hoped to measure a 1761 transit of Ve...

If you’d like to travel into the future – even the far-distant future – you don’t need a time machine. Instead, a starship will do just fine. Fire up the engines, head into space, and keep your foot on the gas.

The laws of physics seem to make it impossible – or nearly so – to travel through time in anything like the modern concept of a time machine – something that allows you to move through the centuries at will. Yet those same laws make it possible to zoom into the future.

The concept is known as time dilation...

Based on the number of books, movies, and TV shows about it, you might assume that traveling through time is almost as easy as ambling through the park on a sunny day: Just build a TARDIS or soup up your Delorean, and off you go.

Alas, the arrow of time moves in only one direction. It allows you to travel into the future, but roadblocks seem to prevent any method that scientists can envision for traveling in the other direction.

Wormholes, for example, are theoretical “tunnels” through space and time. They seem to allow travel to o...

If a cosmic giant sat on a big, gassy planet, it would look a lot like Saturn, the second-largest planet in the solar system. It’s 10 percent wider through its equator than through the poles. But Saturn flattened itself – a result of its low density and fast rotation.

Saturn consists of a series of layers. Its core is a dense ball of metal and rock. Around that is a layer of hydrogen that’s squeezed so tightly that it forms a metal. Around that is a layer of liquid hydrogen – the lightest and simplest chemical element. And the plan...

Building the planets of the solar system was like building a city – it didn’t happen all at once. Instead, it probably took a hundred million years or more to complete the construction project.

The first to be completed were Jupiter and Saturn, the Sun’s largest planets. They came together in the prime real estate for planet building – the region with the most raw materials. Closer to the Sun, it was so hot that ices were vaporized and blown away. Farther from the Sun, the material thinned out. But at the distance of Jupiter and Saturn, the bala...

The 41st episode of a celestial series plays out tomorrow: a total lunar eclipse. It’ll be visible around much of the world – but not the Americas.

Every eclipse belongs to a series, called a Saros. The eclipses in a Saros are separated by 18 years plus 11 and a third days. If we could watch all the eclipses in the cycle play out, we’d see the Moon pass through Earth’s shadow from top to bottom or bottom to top. So the Moon barely dips its toe in the shadow at the beginning and end of the sequence...

The Moon will briefly cover up the tail of the sea-goat tonight – Deneb Algedi, the brightest star of Capricornus. The sequence will be visible across much of the United States.

This vanishing act is an occultation – a type of eclipse in which one object completely covers another. But eclipses are nothing new for Deneb Algedi. Not only does it periodically get covered up by the Moon, but it stages its own eclipses – two of them every day.

What we see as Deneb Algedi is a binary – two stars in a tight orbit around each other. The main...

The planet Jupiter will slide past one of the brighter stars of Gemini the next few mornings. At their closest, they’ll be separated by just a fraction of a degree.

The star is Wasat – from an Arabic phrase that means “the middle.” But the middle of what has been lost over the centuries.

The star also is known as Delta Geminorum – its Bayer designation. The system was devised in the early 17th century by German astronomer Johann Bayer. He named all of the stars in the constellations that were visible from the northern hemisphere. Each star...

Water is the key ingredient for life on Earth. And as far as we know, it’s a key ingredient for life everywhere else in the universe as well. That shouldn’t be a problem, though, because there’s plenty of water to go around.

Water is common in part because it’s made of two of the three most common elements in the universe – hydrogen and oxygen. They come together in the cold of deep space to make grains of ice. Some of those grains are found in the clouds of gas and dust that give birth to n...

Earth is the only body in the solar system with liquid water on its surface. But it’s not the only one where you can find water. In fact, water is everywhere – from comets and asteroids to the giant planets.

Comets and asteroids are chunks of rock, metal, and ices – including water ice. Comets have more ice, but most asteroids probably have large amounts as well. Such bodies might have supplied much of the water on Earth when they collided with our planet billions of years ago.

Water ice is common throughout the solar system. It’s b...

Water is all about extremes. The atoms that make up water molecules were forged in some of the hottest environments in the universe. But most of the molecules formed in the cold of deep space.

A water molecule consists of two hydrogen atoms plus one oxygen atom – H-2-O. A hydrogen atom contains one electron and one proton. The electrons formed in the first fraction of a second after the Big Bang, when the universe was extremely hot and dense. The protons formed a few minutes later.

By about 380,000 years, the universe had expanded and co...

To have a strong heart, you naturally need strong arteries. And that’s not a problem for Antares, the heart of the scorpion. It’s flanked by two fairly bright stars that historically have shared a name: Alniyat – an Arabic name that means “the arteries.”

The stars probably are siblings of Antares. They all formed from the same giant complex of gas and dust, within the past 10 million years or so.

Alniyat I is also known as Sigma Scorpii. It’s a system of four stars. Two of them form a tight pair, with a third close...

A spacecraft that’s on it way to Jupiter is “pinballing” around the solar system, getting an extra “kick” as it zips close to the planets. It’ll get the next kick tomorrow, from Venus.

The spacecraft is JUICE – Jupiter Icy Moons Explorer. It’s scheduled to arrive at Jupiter in 2031. But it needs help to get there. And it gets that help from the gravity of Venus, Earth, and the Moon.

During each encounter, the craft “steals” a bit of gravitational energy. That speeds it up and sculpts its path around the Sun. The encounters drastical...