StarDate

Billy Henry
  • 4.6 (258)
  • ASTRONOMY
  • UPDATED DAILY

StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

Episodes

  1. 1D AGO

    Busy Merger

    There’s nothing like a merger to stir things up. That applies not only to companies and families, but to galaxies as well. One example is Messier 61. A recent merger with a smaller galaxy has brought its central black hole to life, triggered the birth of thousands of new stars. It also kicked out a ribbon of stars that’s as long as the galaxy itself. Messier 61 is a lot like our home galaxy, the Milky Way. It’s about the same size and mass, and it looks about the same – a beautiful spiral with a long bar of stars across its middle. But a close look shows big differences. M61 is giving birth to stars at a much faster rate than the Milky Way. It’s produced more supernovas – the explosive deaths of young, massive stars. The supermassive black hole in its heart is “feeding” much more voraciously. And last year, astronomers discovered a “streamer” of stars behind M61. The streamer is a hundred thousand light-years long, and ten thousand wide. The likely cause of all that activity is a merger with a smaller galaxy. The encounter squeezed big clouds of gas, triggering the starbirth. It provided fresh material for the black hole. And it pulled out stars in the galaxies to form the long tail – stirring things up in a beautiful spiral galaxy. M61 is 55 million light-years away, in Virgo. It climbs into the sky in mid-evening, and sails high across the south later on. It’s an easy target for binoculars. Script by Damond Benningfield

    2 min

  2. 2D AGO

    Grandfather

    A celestial grandfather strolls low across the south on winter evenings. He’s represented by two stars. In the western world, they’re part of the constellation Columba, the dove. But in ancient China they were known as the Grandfather. The stars are Alpha and Epsilon Columbae. Coincidentally, they’re about the same distance from Earth – about 280 light-years. And both are much bigger and brighter than the Sun. But there’s a big difference in their ages, so the stars aren’t related. Alpha – the First Star of Grandfather – is the brighter of the two – the brightest member of Columba. It’s less than a hundred million years old – about two percent the age of the Sun. But it won’t be around much longer. It’s about four and a half times the mass of the Sun. Heavier stars age more quickly. In the next 150 million years or so, Alpha will move out of the “prime” phase of life and into the next phase, as a giant. Epsilon has already reached that phase. It’s not as massive as Alpha, but it’s about one and a half billion years older – a third the age of the Sun. It’s puffed up to many times the size of the Sun, so it shines much brighter. Before long, though, it will cast off its outer layers, leaving only its hot, dead core – and Grandfather will be down to a single star. Columba is low in the south-southeast at nightfall. Alpha and Epsilon are close together, near the center of the constellation. Script by Damond Benningfield

    2 min

  3. 3D AGO

    Winter Milky Way

    On summer nights, Earth faces the heart of the Milky Way Galaxy. That part of the Milky Way features dense clouds of stars. Under dark skies, it’s quite a sight. But during the long, cold nights of winter, we’re facing the opposite direction – toward the galaxy’s edge. So the Milky Way looks thin and faint – a bare ghost of its summer glory. No matter which direction you face, the hazy band of light known as the Milky Way represents the combined glow of millions of stars that outline the galaxy’s disk. The disk is about a hundred thousand light-years wide, but only a few thousand light-years thick. It contains a few hundred billion stars. The center of the galaxy is densely packed, like the downtown of a major city. But its outskirts are like the suburbs. There are fewer stars, and they’re more widely spread. And the closer to the galaxy’s edge, the more thinly spread the stars become. The Milky Way doesn’t end at the edge of the disk. The disk is surrounded by a “halo” of stars and dark matter. It extends hundreds of thousands of light-years into space in every direction. But the halo is like the countryside – a few solitary residents spread far and wide. So nothing in the halo is visible without a good telescope – far outside the galaxy’s disk. The Milky Way arcs high across the sky on February evenings. You need nice dark skies to see it – the thin but still beautiful glow of our home galaxy. Script by Damond Benningfield

    2 min

  4. 4D AGO

    Friday the 13th

    If you walk under a ladder after breaking a mirror, does that make your day doubly unlucky? Since we’re a science program, we’ll say no. But that double-trouble philosophy underpins the superstitions about Friday the 13th. Both Friday and the number 13 have been considered bad luck. Put them together, and you have what may be the most feared of any day-and-date combo. The individual superstitions both have religious and mythological origins. In Christianity, for example, the Last Supper was shared by 13 men. And Jesus was crucified on a Friday. Just when the two were put together isn’t clear. The idea of Friday the 13th being unlucky shows up in some publications in France in 1834. The first record of it in the United States dates to 1882. How many people fear the date isn’t clear, either. But scientists have come up with a couple of names for it. The shorter one, believe it or not, is friggatriskaidekaphobia. Frigg was the Norse goddess for whom Friday is named, and triskaidekaphobia is fear of the number 13. Other than some unlucky teens in the “Friday the 13th” movies, there’s no evidence that the day is any more dangerous than any other. A study in 2011 compared hospital records for 13 Fridays the 13th to other date combinations. There was no bump in the number of emergency-room visits – nothing unlucky about Friday the 13th. Script by Damond Benningfield

    2 min

  5. 5D AGO

    Deep Ocean

    The surface of Ariel looks like a sheet of paper that’s been loosely crumpled. It’s covered with ridges, wrinkles, and gashes. That may be telling us that Ariel once had a deep ocean of liquid water. Ariel is one of the larger moons of the planet Uranus. It’s about 720 miles in diameter – a third the size of our moon. It orbits just a hundred thousand miles from the planet – much closer than the Moon is to Earth. It’s roughly a 50-50 mix of ice and rock. Our only good look at Ariel came in 1986. Voyager 2 flew past it and photographed about a third of its surface. The pictures revealed a complex face. It has a mixture of old and young craters, deep ridges, and smooth plains that might have been paved by water gurgling up from inside the moon. A recent study modeled the orbit of Ariel over the ages. It found that the orbit was once much more lopsided than it is today. As Ariel moved in and out, the gravity of Uranus stretched and squeezed the little moon. That could have melted some of the ice inside it, creating an ocean a hundred miles deep, topped by a thin crust of ice. The stress of all the stretching and squeezing could have cracked the ice, creating the wrinkly surface we see today. Uranus is high overhead at nightfall. It’s below the Pleiades star cluster, and farther to the right of the bright orange star Aldebaran. Through good binoculars, the planet looks like a faint star. Script by Damond Benningfield

    2 min

  6. 6D AGO

    New Identity

    Ursa Major III is doomed. It’s falling apart, and may vanish completely in a couple of billion years. There’s not much to it even now. It’s so faint that it wasn’t discovered until 2023. It contains about 60 stars – all of them ancient, and all much smaller and fainter than the Sun. They add up to only about 16 times the Sun’s mass. They’re packed into a loose ball about 20 light-years wide. But the total mass is about 2,000 times greater than the mass of the visible stars. That’s led to some confusion about its nature. One idea is that it’s a small galaxy that’s orbiting the Milky Way. Most of its mass would consist of dark matter – matter that produces no energy, but that reveals its presence through its gravitational pull on the visible matter around it. A study last year suggested a different nature – a star cluster held together by a clump of black holes. The cluster might have been born with a hundred thousand stars or more. When some of the stars died, they formed black holes, which congregated near the cluster’s middle. The gravity of the Milky Way pulled away many of the cluster’s stars. Encounters with the black holes kicked out many more. And the study says the cluster will fall apart completely in about two billion years. The cluster – or galaxy – is about 30,000 light-years away, in the great bear. But Ursa Major III is far too faint to see, even with a telescope. Script by Damond Benningfield

    2 min

  7. FEB 10

    Pleiades Complex

    Stars are born from huge clouds of gas and dust. Many of the stars remain close together, forming clusters. But as a cluster moves through the Milky Way, it gets pulled apart. The gravity of the rest of the galaxy tugs away the stars on the outskirts of the cluster. It also loosens the rest of the cluster, making it easier to pull away more stars. A recent study looked at how that’s played out in the region around the Pleiades cluster. Using telescopes in space and on the ground, researchers measured how fast the stars in the region are spinning. That provides a rough measure of their age – the younger the star, the faster it spins. They also measured the motions of the stars through the galaxy, allowing them to trace the paths of the stars far into the past. And they compared the compositions of the stars; stars that were born together are made of the same mixture of elements. From that, they found that the Pleiades and several smaller groups were close together tens of millions of years ago. That suggests they were born together before heading their separate ways. The study also found hundreds of stars between the groups that had belonged to one of the groups in the past. Today, the groups and loners are spread across 2,000 light-years of space – the Giant Pleiades Complex. Look for the Pleiades high overhead at nightfall. It looks like a tiny dipper – the heart of a once larger family of stars. Script by Damond Benningfield

    2 min

  8. FEB 9

    Moon and Antares

    Antares is a rare star. It’s one of the few named for what it’s not. The name is Greek. It combines “anti,” which means “against” or “opposed to” – with Ares – the Greek version of Mars, the god of war. So the name means “not Mars” or “rival of Mars.” It was given the name because its color is similar to that of Mars – bright orange. The color indicates that the surface of Antares is thousands of degrees cooler than the surface of the Sun. Cooler stars glow red or orange, while hotter stars are white or blue. Antares is one of many designations for the star. Because it’s the brightest star of Scorpius, it’s also known as Alpha Scorpii. And it’s also called the heart of the scorpion – Cor Scorpii. Antares also has designations in many catalogs – lists of stars that have something in common. It’s in the bright-star catalog as HR 6134. It has a companion star, so it’s in the binary-star catalog. And it’s in several catalogs of objects that produce a lot of infrared light. In all, Antares has dozens of names and catalog numbers – an impressive list for an impressive star. The gibbous Moon slips past Antares the next couple of mornings. The star will be to the left or lower left of the Moon at dawn tomorrow. And it will stand a little closer to the upper right of the Moon on Wednesday. Tomorrow: more stars for the Pleiades. Script by Damond Benningfield

    2 min

  9. FEB 8

    Distant Relative

    Family members don’t always stay close together – they can be separated by thousands of miles. But one member of the Milky Way Galaxy’s family takes the separation to extremes. It’s 300,000 light-years from the center of the galaxy – one of the most distant residents of the Milky Way yet seen. NGC 2419 is a globular cluster – a group of about a million stars. They form a dense ball a few hundred light-years across. Any star near the middle of the cluster would have thousands of neighbors within a few light-years. Compare that to our own neighborhood – only three stars reside less than five light-years from the Sun. NGC 2419 is one of the Milky Way’s oldest family members. The cluster was born more than 12 billion years ago – not long after the galaxy itself. All of its big, bright stars burned out long ago. So almost all of the remaining stars are much less massive than the Sun. The cluster follows a highly stretched-out orbit around the center of the Milky Way. That’s led to suggestions that it was born elsewhere, then captured by the Milky Way. But there’s no confirmation of that idea. So NGC 2419 is still considered a far-away relative of the rest of the Milky Way. The cluster is in the uber-faint constellation Lynx, which is in the east-northeast at nightfall. NGC 2419 is an easy target for just about any telescope. Script by Damond Benningfield

    2 min

  10. FEB 7

    Lynx

    Alpha Lyncis is only about a third of the age of the Sun. Yet the star has already zoomed through the prime phase of life. Now, it’s nearing the end of its life. And it’s letting us know about it – it’s the brightest star of the constellation Lynx. That’s not necessarily saying much. Lynx is a large constellation, but it’s faint – only a few of its stars are bright enough to see from light-polluted cities or suburbs. In fact, the astronomer who created it, in the 1600s, called it “Lynx” because you needed the eyes of one to see it. Alpha Lyncis is classified as a red giant. It’s about half-again the mass of the Sun. Heavier stars age more quickly. Such a star “burns” through the original hydrogen in its core in a hurry. As the core adjusts to the change, the star’s outer layers puff up. Today, Alpha Lyncis is more than 50 times the diameter of the Sun. As it got bigger, the star got cooler and redder – making it a red giant. Puffing up also made the star hundreds of times brighter than the Sun. So Alpha Lyncis is visible – faintly – even though it’s a little more than 200 light-years away. That makes it one of the few stars in this faint constellation that you don’t need the eyes of a lynx to see. Lynx is well up in the east-northeast at nightfall. It’s about half way between the Big Dipper and the twins of Gemini. But you need nice, dark skies to see much. More about the constellation tomorrow. Script by Damond Benningfield

    2 min
  • 10 Episodes

Hosts & Guests

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About

StarDate, the longest-running national radio science feature in the U.S., tells listeners what to look for in the night sky.

Information

  • Creator
    Billy Henry
  • Years Active
    2017 - 2026
  • Episodes
    10
  • Rating
    Clean
  • Copyright
    © 2022 The University of Texas McDonald Observatory
  • Show Website
    StarDate

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