Episode notes
The second-largest asteroid in the solar system is a puzzler. Most studies say it has the same layers as a planet, but that it’s not massive enough to pull itself into a fully rounded shape like a planet. But one study found that it’s not layered at all. Vesta accounts for almost a tenth of all the mass in the asteroid belt. Its average diameter is about 325 miles. But it’s flattened and a bit stretched out. The surface of Vesta is covered with volcanic rock. Combined with other observations, that suggests that Vesta is layered, with a distinct core, mantle, and crust. If so, then it formed…
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StarDate
Billy Henry · Tech & Science · English
StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.
More from StarDate All episodes →
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14 Oct 2026 · 2 minNew
Moon and Antares
Antares, the bright star at the heart of Scorpius, huddles quite close to the Moon early this evening. They set not long after the sky gets dark, so there’s not a lot of time to look for them. The Moon is a thin crescent now, so it’s night across most of the lunar disk. But on the bright sliver that’s in daylight, you can still make out some of the dark lunar “seas” – vast plains of volcanic rock. They formed long ago, when giant asteroids slammed into the Moon. Molten rock bubbled up from below, then cooled and hardened. A recent study found evidence of an especially big impact…
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13 Oct 2026 · 2 minNew
New Crater
The surface of the Moon seems eternal. There’s no air or water to reshape it, and no plate tectonics to jiggle things around. But the Moon does change – sometimes in a hurry. Scientists recently discovered an impact crater that’s almost 750 feet in diameter. It had been gouged during the spring of 2024. The crater was found in images snapped by L-R-O – Lunar Reconnaissance Orbiter. The craft’s been mapping the lunar surface for years. It’s photographed almost all of the surface many times. Scientists compare images taken at different times to see how things have changed. The new impact…
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11 Oct 2026 · 2 min
Messier 10
The stars in a binary system can be quite intimate. One star can pull gas off the surface of its companion, for example. And in extreme cases, the stars can merge to form a single star. Both types of interactions can make the stars look a lot younger than they really are. Many examples of this are found in Messier 10. It’s a globular cluster – hundreds of thousands of stars all packed into a ball a few dozen light-years across. The cluster includes an especially large number of blue stragglers – stars that look a lot younger and bluer than the cluster should contain. M10 itself is billions…
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10 Oct 2026 · 2 min
Double Cluster
A pair of big, young star clusters is one of the skywatching highlights of autumn evenings. Each cluster contains thousands of stars. And hundreds of those stars are especially impressive – supergiants that are many times the size and mass of the Sun, and many thousands of times brighter. The clusters are NGC 869 and 884. Together, they’re known as the Double Cluster. They’re in the northeast at nightfall, in the constellation Perseus the hero. Under dark skies, they’re visible to the eye alone as a single smudge of light. Binoculars split them apart, revealing two sparkling collections of…
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9 Oct 2026 · 2 min
Caroline’s Rose
Cassiopeia is an easy constellation to pick out. The stars of the queen form a prominent letter M or W, which is visible even through moderate light pollution. And under dark skies, binoculars reveal several star clusters around that pattern, all immersed in the glow of the Milky Way. One of the highlights is NGC 7789. It was discovered in 1783 by Caroline Herschel – the first woman to be paid for her work as an astronomer. Through a telescope, the contours of the cluster and nearby clouds of dust resemble a rose. So NGC 7789 also is known as Caroline’s Rose. The cluster is about 6800…
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8 Oct 2026 · 2 min
Quiet Monster
A quiet monster lurks in the heart of M31, the Andromeda Galaxy. Known as M31-star, it’s a black hole a hundred million times the mass of the Sun, and 25 times heavier than the black hole at the heart of the Milky Way. Every large galaxy probably has a supermassive black hole. And many of them are quite bright. The black hole itself is completely black – it swallows up all the matter and energy that falls into it, and nothing can come back out. But the black hole’s gravity pulls in huge amounts of gas and dust, along with an occasional asteroid, star, or other large object. This debris forms…
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7 Oct 2026 · 2 min
Andromeda Galaxy
Two-and-a-half million years ago, Earth was going through some big changes. It was the start of the Pleistocene epoch – a period of major ice ages. And the ancestors of modern humans were just appearing. That timescale puts a little perspective on the distance to M31, the Andromeda Galaxy – the closest major galaxy to the Milky Way. It’s two-and-a-half million light-years away. So when we look at the galaxy, we’re seeing it as it looked two-and-a-half million years ago. Andromeda and the Milky Way are much alike. Both of them are barred spirals – they have a long bar of stars in the center,…
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