StarDate

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

ตอน

  1. 1 วันที่แล้ว

    Deneb

    The bright star that marks the tail of the swan is big, bright, and heavy. If you want to know how big, bright, and heavy, well, the most precise answer we can give you is “very.” We know for sure that Deneb is one of the more imposing stars around. But the details are a little hazy because the star’s distance is hazy. In part, that’s because of Deneb’s impressiveness. The most accurate stellar distances come from Gaia, a space telescope. But Deneb is so bright that Gaia can’t look at it directly. Instead, it has to study the star indirectly – sort of like checking something out through the corner of its eye. It takes a lot of work to translate those glimpses into solid numbers. In addition, the star’s outer layers are puffy and unstable, so it’s hard to know just where its surface is. And you need a good idea of the surface to measure the star’s location. The best estimates say that Deneb is about 1500 light-years away – one of the most remote stars that’s visible to the eye alone. But other estimates say it’s almost twice that far. So based on that range, Deneb is about 15 to 20 times the mass of the Sun, 100 to 200 times the Sun’s diameter, and 50 thousand to 200 thousand times its brightness – impressive numbers for a very impressive star. Deneb is a third of the way up the northeastern sky at nightfall, and soars high overhead during the night. Script by Damond Benningfield

    2 นาที

  2. 2 วันที่แล้ว

    Prominent Sun

    When the Moon covers the Sun during a total eclipse, a couple of rare sights greet viewers. One is the corona – the Sun’s hot but thin outer atmosphere, which looks like a silvery halo. The other is the short red or pink tendrils known as prominences – eruptions of gas into the corona. They’re actually there all the time, but they’re impossible to see against the brilliance of the Sun’s disk. Prominences can span many thousands of miles; the largest are about half the size of the Sun itself. They’re actually thousands of degrees cooler than the surface of the Sun. They look bright only when they’re seen against the dark background of space. When they’re seen against the Sun, they form dark streaks. Prominences are powered by the Sun’s magnetic field. Strands of the field can levitate above the surface. The strands can be filled with plasma – hot gas that has an electric charge. Some prominences are common around magnetically active regions. They can erupt in minutes, loop into the corona, then collapse within hours. Others form in regions that are fairly quiet. They can take days to bloom into the corona, then remain visible for weeks or months. Some prominences don’t stop at the corona. They can send huge clouds of plasma into the solar system. If they hit Earth, these outbursts can trigger brilliant auroras and disrupt technology – prominent impacts from the Sun. Script by Damond Benningfield

    2 นาที

  3. 3 วันที่แล้ว

    Tarazed

    To predict the lifespan of a star, you don’t need a crystal ball – a bathroom scale will do just fine. Heavier stars age faster, so if you know the star’s mass, you have a good idea of its future. Consider Tarazed, the second-brightest star of the eagle. It’s only about six percent the age of the Sun. But because it’s about three and a half times the Sun’s mass, it’s already completed the “prime” phase of life. Now, it’s well into the next phase – as a red giant. Mass is critical because, as the star’s mass increases, so does its gravity. Stronger gravity squeezes the star’s core more tightly, increasing its temperature. That revs up the rate of nuclear reactions in the core. When a star is born, its core is mostly hydrogen. In the prime phase of life, the star “fuses” the hydrogen atoms to make helium. When the hydrogen is gone, the core shrinks, so it gets even hotter. That causes the star’s outer layers to puff up, which is what’s happened to Tarazed – it’s more than 90 times the Sun’s diameter. Higher core temperatures trigger the next round of reactions. So today, Tarazed is fusing the helium to make heavier elements. Eventually, that will end as well. Tarazed will shed its outer layers, leaving only its tiny, dead core – ending the star’s fairly short but bright life. Tarazed is low in the east at nightfall. It’s close above even brighter Altair, at the southern point of the Summer Triangle. Script by Damond Benningfield

    2 นาที

  4. 4 วันที่แล้ว

    Altair

    Altair is one of the highlights of summer. It’s at one point of the Summer Triangle, and it’s the twelfth-brightest star in the night sky. And it’s just 16.7 light-years away. Because Altair is so close and bright, we know quite a bit about it. And we’re learning more all the time. A study a couple of years ago, for example, refined the likely age of the star – 88 million years, give or take 10 million. That’s just two percent the age of the Sun. Altair is about twice the size and mass of the Sun. And because it’s so young, it spins in a hurry – one turn every eight hours or so, versus 25 days for the Sun. That whirling rotation makes the star look squished – it’s about 25 percent wider through the equator than the poles. In 2022, astronomers “listened” to the star with a space telescope. It measured vibrations on the surface of the star. Combined with observations from the ground, that revealed a total of 34 vibration modes – like 34 different musical notes. The vibrations travel deep into the star. Each “note” reveals details about Altair’s interior. Piecing together the whole symphony, the astronomers found that the core of Altair contains more than 97 percent of the hydrogen it was born with. As a star ages, it converts its hydrogen to helium. So the amount of hydrogen reveals that Altair is just starting out. Script by Damond Benningfield

    2 นาที

  5. 5 วันที่แล้ว

    Moon and Antares

    A wave of starbirth is sweeping through Scorpius and some nearby constellations. It started about 20 million years ago, and is continuing today. It’s triggered the birth of thousands of stars, including some of the most impressive in our part of the galaxy. The complex is called the Scorpius-Centaurus association. It consists of three distinct regions that appear to be related. Giant clouds of gas and dust in one of those regions began collapsing tens of millions of years ago. That gave birth to the first stars in the association. The most massive members of that group produced winds and radiation that squeezed the surrounding clouds. And some of those early stars exploded, creating shockwaves that compressed the clouds even more. That triggered the birth of many more stars. Many stars in the association are extremely big, bright, and massive. They account for many of the bright lights that outline the scorpion, the centaur, and other constellations in the region. For every one of those stars, there are hundreds of less-massive stars. From Earth, the most impressive member of the association is Antares, the heart of the scorpion, which is quite near the Moon tonight. Antares is more than a dozen times the mass of the Sun, and tens of thousands of times brighter. In the next million years it’s likely to explode as a supernova – perhaps triggering the birth of even more stars in this busy complex. Script by Damond Benningfield

    2 นาที

  6. 6 วันที่แล้ว

    The Stinger

    Two stars that sound a bit scary peek above the southern horizon on summer nights. Together, they form the “stinger” – the end of the curving body of the scorpion. The stars are Lambda and Upsilon Scorpii. Lambda is the brighter of the two. It’s also the more complicated – it consists of three stars. The system’s details are a bit uncertain. That’s largely because its distance is uncertain. Estimates range from about 365 light-years to almost twice that range. Without a good measurement of the distance, it’s tough to figure out how big and heavy the stars really are. We do know that the system consists of a tight binary – two stars that orbit each other once every six days – plus a third star that orbits the others every three years. One of the stars in the binary is much bigger and brighter than the Sun, and 10 to 14 times the Sun’s mass. That means the star will end its life with a colossal explosion. Its close companion is maybe twice the mass of the Sun. But it’s not yet fully formed. The distant companion is another big guy – roughly 8 to 10 times the mass of the Sun. If it’s at the high end of that range, then it, too, will explode as a supernova. If not, its fate is less certain. It could become a supernova, but it also might expire in a more gentle process – a fate similar to the Sun’s. More about the scorpion tomorrow. Script by Damond Benningfield

    2 นาที

  7. 24 มิ.ย.

    U Scorpii

    A star system on the far side of the galaxy keeps blowing up. Since 1863, astronomers have recorded 12 outbursts from the system – the most recent just four years ago. The flare-ups are powered by a complicated interplay between a dead star and a companion that may be dying. U Scorpii probably is more than 60,000 light-years away, far on the other side of the heart of the Milky Way Galaxy. Most of the time, the system is quite faint. But during the outbursts, it can flare 10,000 times brighter in just a few hours. It starts to fade quickly, but it takes about two months to return to its “quiet” state. The system consists of two stars in a tight orbit. One of them is a white dwarf – the dead core of a Sun-like star. The other star is headed toward the same fate. It’s at the end of the prime phase of life, so it’s starting to puff up. The white dwarf “steals” some of the gas from its surface, forming a swirling disk. Some of the gas piles up on the white dwarf. Eventually, the gas gets so hot, it sets off a nuclear blast, making the system flare up. The outburst blows away all or part of the disk. Before long, though, the process starts all over again – leading to another explosion a few years later. U Scorpii is in Scorpius, which is low in the south-southeast at nightfall. The system is above the curving line of stars that outlines the scorpion’s body and tail. Script by Damond Benningfield

    2 นาที

  8. 23 มิ.ย.

    Microquasar

    About 10,000 light-years from Earth, a dead star is devouring its living companion. The process creates a disk of gas that’s heated to millions of degrees, so it shines brightly. Some of the gas is fired back into space at almost the speed of light, adding to the fireworks. The system is so powerful that it’s classified as a microquasar – a smaller version of some of the brightest objects in the universe. GRO J1655-40 consists of a black hole about six or seven times the mass of the Sun, plus a close companion star more than twice the Sun’s mass. The black hole probably began as a star about 25 times the Sun’s mass. It evolved quickly, with its core collapsing to form the black hole. Its outer layers were blasted into space. Some of that material fell on the companion. Today, the black hole is pulling some of that gas away from the companion. The same thing happens in the cores of many remote galaxies. Supermassive black holes create monster disks as they pull in gas, dust, and stars. Such a disk can shine billions of times brighter than the Sun – forming a quasar. GRO J1655-40 is a smaller version of that. The system is in Scorpius, which crawls across the south on summer evenings. The microquasar is near where the scorpion’s body curves to form its tail. Script by Damond Benningfield

    2 นาที

  9. 22 มิ.ย.

    The Scorpion’s Head

    It’s hard to see a pattern in most of the constellations. Their stars are too faint or too spread out, or the pattern is just too obscure. Perhaps the most prominent exception is Scorpius. It takes little imagination to see the curving body of a scorpion in its stars. The scorpion skitters low across the south on summer nights. Its brightest star is Antares. The scorpion’s body and tail curl to the lower left. The head is to the upper right. It’s marked by a line of three stars. They’re about the same brightness, and they’re fairly evenly spaced. From top to bottom, the stars are Beta, Delta, and Pi Scorpii. Delta is a bit brighter than the others. All three stars are extraordinary. Each of them actually consists of more than one star. All of the member stars are quite young – no more than a few percent the age of the Sun. And most of them are big and heavy, with some of them fated to end their lives as supernovas – titanic explosions that will outshine billions of normal stars. Delta Scorpii consists of two stars. At least one of them will become a supernova. Pi Scorpii is a triple system. It also features at least one future supernova. Beta is the busiest of the systems – at least six stars, all orbiting each other in a complex gravitational ballet. Two of those stars are likely to become supernovas – briefly highlighting the head of the scorpion. Script by Damond Benningfield

    2 นาที

  10. 21 มิ.ย.

    Equation of Time

    Our clocks tick off a steady 24 hours per day. But if a sundial could record the time with the same accuracy, it would show that the length of the day changes. The difference is called the equation of time. Clocks measure the length of a day averaged over a full year – the Sun’s average motion across the sky. Sundials show the Sun’s true motion. Over the course of a year, the length of a solar day – the period from one local noon to the next – varies by almost a minute. And that adds up. In early February, a solar day lasts about 14 minutes less than 24 hours. In early November, it lasts about 16 and a half minutes more than 24 hours. The change has a couple of causes. Earth’s orbit is lopsided, so our planet travels at different speeds. When we’re closest to the Sun, we move faster than average; when we’re farthest, we move slower. But the rate at which Earth spins on its axis remains the same. The difference in those two motions causes the Sun to move a little faster or slower across the sky, changing the length of a solar day. And Earth’s axis is tilted, so the poles take turns dipping toward the Sun. Today is the June solstice, so the north pole is tilting sunward. The change in the Sun’s position as a result of that tilt adds to the complexity. The solar day is exactly 24 hours long around June 13th. So now, the equation of time is almost zero – a close match between the sundial and the clock. Script by Damond Benningfield

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

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  • ผู้จัดทำ
    Billy Henry
  • ออกอากาศปี
    พ.ศ. 2560 - พ.ศ. 2569
  • ตอน
    10
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    © 2022 The University of Texas McDonald Observatory
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