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Latest Episodes:

Deep Search Oct 03, 2025

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 is called a WIMP – a weakly interacting massive particle. Although dark matter almost never interacts with normal matter, it might occasionally do so – ramming into the nucleus of a normal atom. That would produce a tiny spark of light, which detectors might see.

One experiment is LUX-ZEPLIN. It’s in a former gold mine, almost a mile below the town of Lead, South Dakota. The rock above it blocks other types of particles from reaching the experiment.

Its detectors are inside a vat filled with about 8,000 tons of liquid xenon. The hope is that a WIMP will hit a xenon molecule and trigger that spark of light.

Project scientists conducted 280 days of observations. And they didn’t find any indication of WIMPs. But their test was the most sensitive yet for certain types of WIMPs. So the experiment rules out some candidate particles – narrowing the possibilities for dark matter.

Script by Damond Benningfield

Ceres Oct 02, 2025

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 quarter the diameter of the Moon. It probably consists of a dense core and mantle surrounded by an icy crust.

The Dawn spacecraft studied Ceres from orbit a decade ago. It saw big patches of bright, salty minerals. It also saw mountains, including one that’s three miles high; if you scaled Ceres to the size of Earth, the mountain would be 40 miles high. And the craft discovered that much of the surface consists of minerals that formed in a wet environment. So Ceres has water, heat, and organic compounds – the basic ingredients for life in what looks like an unfriendly world.

Ceres is at a point called opposition – it lines up opposite the Sun in our sky. That means it rises around sunset and is in view all night. It’s also closest to us at opposition, so it shines at its brightest. Even so, you need binoculars or a telescope to pick it out, in the constellation Cetus.

Script by Damond Benningfield

Armed Constellations Oct 01, 2025

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 Botes the herdsman. Like many of the ancient star figures,

Botes 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, it’s a spear.

Well above Botes is Hercules, marked by a lopsided box of four stars. He’s wrestling the multi-headed hydra. And in some depictions, he’s holding up a club.

In the south, look for Sagittarius. To modern eyes, it forms the outline of a teapot. But to the ancients, those stars formed an archer. The star at the outer edge of the spout is the point where he’s gripping both bow and arrow.

And low in the northeast there’s a figure with a unique weapon. Perseus the hero is holding the head of Medusa. In mythology, anyone looking at Medusa was turned to stone. Perseus managed to sever the head, then used it to save the princess Andromeda from a monster.

And if you’re stargazing before dawn, there’s another armed figure, well up in the south: Orion the hunter. He has two weapons. He’s holding a club in an upraised arm, with a sword strapped to his belt – a heavily armed figure in the stars.

Script by Damond Benningfield

More Fomalhaut Sep 30, 2025

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 hundred times the distance from Earth to the Sun.

Fomalhaut is only about one-tenth the age of the Sun. Even so, it’s old enough that it should have blown away most of the dust. The fact that the belts are so prominent – especially the outer belt – means that they’re being renewed. The most likely source is collisions between large comets or asteroids. As those bodies are destroyed, they spew dust out into space.

One estimate says it would take the destruction of 2,000 comets that are one kilometer in diameter every day to keep the belts going. The would-be planet was the result of a collision between two even larger objects – briefly creating the illusion of a giant planet around this bright star.

Fomalhaut is low in the southeast at nightfall, and climbs across the south later on.

Script by Damond Benningfield

Fomalhaut Sep 29, 2025

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 contain planets; more about that tomorrow.

Fomalhaut has two companion stars – bound to it by their mutual gravitational pull. Both stars are smaller, cooler, and fainter than the Sun. One of them is barely visible to the eye alone, but you need a telescope to see the other.

Both stars are a long way from Fomalhaut itself. One is almost a light-year away, while the other is two and a half light-years. Astronomers know they’re bound to Fomalhaut because they’re moving in the same direction and at the same speed. Their composition is similar to Fomalhaut’s as well, and so is their age.

Fomalhaut itself will shine for another few hundred million years. But the companions will last much longer – billions of years for the larger one, and hundreds of billions of years for the other. So they’ll still be shining across the galaxy long after the demise of their showy companion.

Script by Damond Benningfield

Odd Alignment Sep 28, 2025

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.

Astronomers have spent years watching M31’s entourage with Hubble Space Telescope. They recently reported that 36 of the 37 brightest members line up on the side of M31 that faces the Milky Way. And that’s hard to explain.

The study said there’s only a tiny chance that the alignment is a coincidence – there must be a reason for it. But no one knows what that reason might be.

It’s not a result of the Milky Way’s gravitational pull – it’s not strong enough. So there’s no obvious explanation for why M110 is an oddball – lurking on the far side of M31.

M31 is low in the northeast at nightfall. Under dark skies, it looks like a hazy slash of light about as wide as the Moon. Through a small telescope, M110 looks like a bright star close by.

Script by Damond Benningfield

Moon and Antares Sep 27, 2025

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 make a quasi-moon as the result of an impact. The study team simulated tens of thousands of impacts across the entire Moon, at different lunar phases and with different ejection speeds. The results showed that it’s pretty darned easy. Almost seven percent of the simulations produced objects that share Earth’s orbit. And two percent became quasi-moons. They can remain in stable orbit near Earth for thousands of years before they’re kicked away.

A Chinese spacecraft is scheduled to visit one of the quasi-moons next year. It’ll collect a few ounces of dirt and pebbles and return them to Earth for study. That should tell us whether the object is a chip off the ol’ Moon, or an interloper from elsewhere in the solar system.

The Moon has a bright companion tonight: Antares, the brightest star of Scorpius. It’s close to the right of the Moon as they drop down the western sky in early evening.

Script by Damond Benningfield

Avoiding a Collision Sep 26, 2025

The closest giant galaxy to the Milky Way is Messier 31, the Andromeda Galaxy. It’s two-and-a-half million light-years away. But it’s getting closer – by about 250,000 miles every hour.

For more than a decade, in fact, it’s looked like the two galaxies were on a collision course. But a recent study says there’s only a 50-50 chance of a collision and merger. And if it does happen, it’ll take place billions of years later than previous estimates.

The new study used years of observations by two space telescopes – Hubble and Gaia. Researchers plugged those observations into simulations that also considered the gravitational effects of two smaller galaxies. The results indicated that one of them tends to push Andromeda and the Milky Way together, while the other tends to pull them apart.

The researchers ran a hundred thousand simulations. In half of them, Andromeda and the Milky Way flew past each other and went their own ways. In the other half, they eventually spiraled together and merged – but not for at least 10 billion years – twice as long as earlier estimates.

The simulations aren’t the final word – there are just too many uncertainties. But for now, it seems likely that the two giants will stay apart for a long, long time.

M31 is in the northeast at nightfall. Under dark skies, it’s visible as a hazy patch of light. Binoculars make it easier to pick out.

Script by Damond Benningfield

Galactic Empire Sep 25, 2025

Messier 31, the Andromeda Galaxy, is the largest and most-distant object that’s easily visible to the unaided eye. Under dark skies, it looks like a skinny cloud about as wide as the Moon. Right now, it’s about a third of the way up in the northeast at nightfall.

M31 is two-and-a-half million light-years away. In other words, the light you see from the galaxy tonight began its journey across the cosmos two-and-a-half million years ago. The galaxy is roughly 150,000 light-years across – bigger than the Milky Way – and may contain a trillion stars.

It’s also the hub of its own galactic empire – it’s orbited by more than three dozen smaller galaxies. And a recent study revealed many new details about the satellites. Astronomers spent years looking at them with Hubble Space Telescope. And they supplemented the new observations by going through older ones.

They found that most of the stars in the smaller galaxies had been born by about 12 billion years ago – when the universe was about one-tenth of its present age. And star formation had all but stopped by about eight billion years ago. Galaxies that are bigger and farther from M31 gave birth to stars a little longer than those that are small and close.

One of the bigger satellites might have rammed through M31 a few million years ago. That stirred things up throughout the empire surrounding big, beautiful M31.

More about M31 tomorrow.

Script by Damond Benningfield

Geoffrey Burbidge Sep 24, 2025

People become astronomers for many reasons: They’re interested in the workings of the stars, or the quest to find life in the universe, or the fate of the universe itself. Geoffrey Burbidge joked that he became an astronomer because he married one. He and his wife, Margaret, were astronomy’s power couple.

And they co-authored one of the most important studies of the 20th century.

Burbidge was born 100 years ago today, in the English village of Chipping Norton. He first studied history, but switched to physics. After earning his undergraduate degree, shortly after World War II, he developed bombs for a while. Back in academia, he married Margaret, and they hopped around England and the United States over the next few decades.

Burbidge contributed to many areas of astronomy theory. But he’s best known for a single paper, known as B-squared-F-H for the names of its authors – the two Burbidges, William Fowler, and Fred Hoyle.

In it, they explained how stars forge most of the elements in the universe. Many elements are created in a star’s core during its long life; others, in the violent deaths of stars. Some of the elements are expelled into space, where they can be incorporated into new stars. The newer generations make even more elements – eventually creating the chemistry we see in the universe today. So the paper showed that we’re all made of “starstuff” – elements created in the stars.

Script by Damond Benningfield

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