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.

Afleveringen

  1. 1 dag geleden

    More ‘G’ Stars

    The Sun belongs to a rare class of stars: Class G. Members of this class account for only seven or eight percent of all the stars in the Milky Way Galaxy. A star’s class is determined by its surface temperature, which we see as its color. G stars are in the middle of the temperature scale, so they shine yellow or yellow-white. Most class-G stars are in the prime of life – a span that puts them on the main sequence. They’re steadily “fusing” the hydrogen in their cores to make helium. And most of them will stay in that phase of life for 10 billion years or longer. Most of them are within about 15 percent of the mass of the Sun. Any heavier and they’d get hot enough to move up to class F or higher. Any lighter and they’d be cool enough to move down to class K or M. Main-sequence G stars are only a small fraction of the size, mass, and brightness of the top stars. But the stars in higher classes are even more rare than G stars. So the Sun, which is near the top of its class, shines brighter than about 90 percent of the stars in the Milky Way. Not all G stars are on the main sequence, though. Some are bloated and heavy. Such stars are more massive than the Sun. They’ve burned through the hydrogen in their cores, and are fusing hydrogen in a thin shell around the core. But they’re undergoing a transition, so they won’t stay yellow for long – the short-lived monsters of class G. Script by Damond Benningfield

  2. 2 dgn geleden

    G Stars

    Under a dark sky, far from city lights, the eye alone can see thousands of stars. They come in a variety of brightnesses and colors. Yet only a few of those pinpoints are like the Sun. Stars are classified based on their surface temperature, which is indicated by their color. Hot stars are blue and white, while cool stars are orange and red. The Sun is in the middle, shining yellow-white, with a surface temperature of about 10,000 degrees Fahrenheit. Those traits mean it’s class “G.” From hottest to coolest, stars are classified with the letters O, B, A, F, G, K, and M. Each class is divided into 10 sub-categories. And each star is given a Roman numeral that indicates its size and its stage in life. The Sun is class G2V. That means it’s toward the hot end of class G, and that it’s on the “main sequence” – it’s in the prime of life, converting the hydrogen in its core to helium. A couple of moderately bright G main-sequence stars are in view by late evening. 51 Pegasi is high in the southeast, while Tau Ceti is just climbing into view far below it, close to the horizon. The brightest class G main-sequence star visible from Earth is Alpha Centauri A. It’s the leading light of a triple star system that’s a bit more than four light-years away – closer than any other stars. It’s so far south, though, that it’s visible from only a tiny sliver of the United States. More about G stars tomorrow. Script by Damond Benningfield

  3. 3 dgn geleden

    Moon and Jupiter

    To borrow from an advertising campaign, Jupiter is “getting the red out.” Its enormous “eye” – the Great Red Spot – has been shrinking. It’s now just a third as wide as when it was first seen, and it’s getting smaller all the time. The Great Red Spot is one of the most recognizable features in the solar system. But scientists still don’t know that much about it. They don’t know for sure how it formed, why it’s shrinking, or even why it’s red. They have lots of ideas, but no certain answers. The spot was discovered as early as 1831. There were suggestions that it was seen much earlier, but those sightings might have been a different feature. The spot has been tracked on a regular basis since 1878. It’s between two powerful jet streams. They prevent it from wandering to different latitudes. It tops out several miles above the surrounding clouds, and extends at least 150 miles below the clouds. In the late 19th century, the spot was a long oval – about as tall as Earth, but three times as wide. Today, it’s roughly the same size as Earth. And the rate of shrinkage has been increasing. So it’s possible that it could disappear entirely within a few decades. Look for Jupiter close below the Moon at dawn tomorrow. It looks like a brilliant star. The Great Red Spot is visible through a telescope, but whether it’s visible from a particular location depends on the timing. Script by Damond Benningfield

  4. 4 dgn geleden

    Moon and Companions

    The Moon anchors a prominent triangle in tomorrow’s early-morning sky. The pattern is well up in the east at first light. The stars Pollux and Castor – the twins of Gemini – line up to the upper left of the Moon, with Mars to the upper right. The brilliant planet Jupiter stands well below the triangle. Mars and Pollux are almost exactly the same brightness right now. And they’re the same color: orange. But they achieve that color in different ways. Mars is a planet – a ball of rock and metal that’s smaller than Earth. Its color comes from iron oxide – particles of rust – in the rocks and dust that cover most of its surface. The rust probably formed when iron-rich rocks interacted with liquid water on the surface. But there’s no water on the surface today. So the rocks must have rusted billions of years ago, when Mars was much warmer and wetter than it is today. As the rocks eroded, the Martian winds carried the dust around the globe – enhancing the color of the Red Planet. Pollux, on the other hand, is a star. It completed the prime phase of life, then puffed up to giant proportions – about nine times wider than the Sun. As it expanded, it got cooler. And a star’s color is determined by its surface temperature; cool stars look red or orange. So just by looking at it, we can tell that Pollux is thousands of degrees cooler than the Sun. We’ll talk about the Moon and Jupiter tomorrow. Script by Damond Benningfield

  5. 5 dgn geleden

    Moon and Mars

    Some of the most imposing features on Mars are its giant volcanoes. The largest is Olympus Mons. It’s more than 13 miles high, and covers an area as big as New Mexico. It’s part of the largest complex of volcanoes on the planet – a region called Tharsis Ridge. The second-largest group is on Elysium Rise. Its largest member is Elysium Mons. It’s the fourth-highest mountain on the planet. It has an elevation of about 10 miles above the Martian equivalent of “sea level,” and it towers about eight miles above the surrounding plains. Like the other major volcanoes, it’s extinct – or at least dormant. It probably hasn’t erupted in hundreds of millions of years. It formed over billions of years, from layers of lava and ash. It’s marred by many craters. Some of them are impact craters, carved by giant space rocks. Others may be volcanic vents, formed by side eruptions of gas or lava. The volcanoes on Mars have grown so big mainly because there are no plate tectonics. Once a pool of magma forces its way to the surface, it just keeps going – the crust above it doesn’t move away. So there’s no “cut-off” valve – the volcano erupts as long as there’s molten rock below to keep feeding it – building some giant mountains on the Red Planet. Mars appears below the Moon in tomorrow’s early morning sky. It looks like a fairly bright orange star. More about the Moon and its companions tomorrow. Script by Damond Benningfield

  6. 6 dgn geleden

    Red and Black

    Little Red Dots might be like Tootsie Roll Pops: colorful on the outside, dark on the inside. They may consist of a glowing cloud of gas and dust encircling a supermassive black hole. And they could be telling us about the birth of the first big black holes in the universe. Little Red Dots were first seen in 2022, by Webb Space Telescope. Since then, it’s discovered hundreds of them. They’re compact but extremely bright. And they’re so far away that we see them when the universe was no more than about one-tenth of its current age. Astronomers have proposed several explanations for them. One is the idea of a black hole surrounded by gas and dust. A recent study looked at a dot that was behind a huge cluster of galaxies. The cluster’s gravity magnified the view of the dot, making it easier to suss out its details. Its heart is a black hole about 50 million times the mass of the Sun. The surrounding cloud is no more than half that mass. As material in the cloud funnels inward, it gets hot, lighting up the rest of the cloud. The gas and dust absorb blue light, so we see only red. Astronomers have pondered the formation of early galaxies for decades. They’ve wondered whether the giant black holes in their hearts formed first, or if the galaxy came first and the black hole formed later. The new finding suggests that, in at least some cases, the black hole came first – born at the heart of a Little Red Dot. Script by Damond Benningfield

  7. 3 sep

    Third-Generation

    In the past decade, astronomers have “heard” almost 400 mergers between black holes. The signals were carried by gravitational waves – tiny ripples in spacetime. They’ve revealed that some of the black holes probably had undergone earlier mergers – making them third-generation black holes. Gravitational waves are produced by the motions of any object. But the waves are extremely weak. So far, the only ones that have been detected were produced by mergers involving black holes or neutron stars – dense, heavy objects that come together in a fraction of a second. The characteristics of the waves reveal the masses of the merging objects. They also reveal how the objects were spinning, and how they were orbiting before the merger. And those details provide hints to the existence of third-generation black holes. One example was discovered in late 2024. A black hole about 20 times the mass of the Sun merged with one about six times the Sun’s mass. Scientists determined that the heavier black hole probably formed from an earlier merger. They even calculated the details of those black holes: about 7 and 13 times the mass of the Sun. Third-generation black holes probably form in places where lots of black holes are jammed close together, such as the hearts of star clusters. That keeps a merged black hole from escaping – setting up the possibility of more mergers ahead. Script by Damond Benningfield

  8. 2 sep

    Moon and Pleiades

    The Moon charges at the Pleiades late tonight. As seen from most of the United States, it will pass especially close to the star cluster – either just skimming its edge or briefly covering some of its stars. The cluster is home to more than a thousand stars of all varieties. The ones that are visible to the eye alone are especially big, hot, and bright. But they’re greatly outnumbered by stars that are much smaller, cooler, and fainter. Many of the stars belong to systems of two stars or more. And the cluster also hosts many “brown dwarfs” – objects that are more massive than planets, but not heavy enough to shine as true stars. Over the decades, there’s been a lively debate about the distance to the cluster. Different telescopes and techniques have provided measurements that vary by many light-years. The best current number puts the distance at about 440 light-years. But that’s the distance to the center of the Pleiades. The cluster actually spans several dozen light-years in all directions. So as you look at the cluster, the light you see from the stars that are closest to Earth headed our way dozens of years earlier than the light from the stars that are farthest – an out-of-sync view of a well-known star cluster. The cluster’s brightest stars form a tiny dipper shape, although it’ll be tough to make out through the moonlight. The cluster will be especially close to the Moon at dawn. Script by Damond Benningfield

  9. 1 sep

    Roman Telescope

    The center of the Milky Way Galaxy is packed with treasures: stars, dead stars, gas clouds, and lots of planets. And a new space telescope will spend a lot of its time sorting it all out. That’s one of several big projects for Nancy Grace Roman Space Telescope, NASA’s next big space observatory. The telescope will see the heavens as clearly as Hubble Space Telescope does. But its view will be much wider. And it’ll study the universe mainly in the infrared – wavelengths that are invisible to the human eye. Roman will tackle some of the biggest problems in modern science. As one example, it’ll look away from the center of the Milky Way to study more than a billion other galaxies, and to look for exploding stars. That combination will help us understand how the universe is expanding – a key for deciphering the mystery of dark energy. The telescope’s survey of the center of the galaxy could reveal thousands of new planets. And a special instrument – using a technique proposed by Nancy Roman herself – could provide images of some of those planets. A planet will appear only as a bright dot, with no detail. But breaking down its light will tell us a bit about the planet’s size, temperature, and composition. The center of the Milky Way is in Sagittarius, which is low in the south at nightfall. Its brightest stars outline a teapot. The heart of the galaxy is in the steam above the spout of the teapot. Script by Damond Benningfield

  10. 31 aug

    Venus and Spica

    The planet Venus and the star Spica huddle close the next few evenings. They’re quite low in the west-southwest in early twilight. Venus is the brilliant “evening star.” Tonight, Spica stands close above it. Venus will slide to the left of Spica over the following nights. Venus is named for the Roman goddess of love and beauty. It’s the only major planet in the solar system named for a female character. With a few exceptions, all of the features on its surface are named for women as well – from both mythology and real life. No features were named until the Space Age. Venus is covered by an unbroken blanket of clouds, so we can’t see the surface. Radio telescopes on Earth peered through the clouds in the ’60s, and discovered the first known features. All the other features were mapped by spacecraft in orbit around Venus, which scanned the planet with radar. Today, more than 2,000 features have been named – mountains, craters, canyons, plains, and others. Their names have come from cultures around the world and across the ages. One volcano is named Anuket, for an Egyptian river goddess, while another is named La Shen for a Chinese goddess. Other features are named for Anne Frank, Jane Austen, Pocahontas, and Queen Isabella of Spain, along with other writers, artists, rulers, scientists, and women from many other fields – all commemorated on the planet Venus. Script by Damond Benningfield

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Info

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

Informatie

  • Maker
    Billy Henry
  • Jaren actief
    2017 - 2026
  • Afleveringen
    10
  • Beoordeling
    Veilig
  • Copyright
    © 2022 The University of Texas McDonald Observatory
  • Website van aflevering
    StarDate

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