StarDate

Billy Henry
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  • ASTRONOMY
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StarDate

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

Episodes

  1. 1 DAY AGO

    Moon and Spica

    The next total eclipse of the Sun is almost two years away. But astronomers will watch many “total eclipses” between now and then. Known as occultations, they occur when one astronomical object passes in front of another, blocking the more distant one from view. The most frequent “blocker” is the Moon. And early tomorrow it’ll block out Spica, the brightest star of Virgo. Spica is just two degrees from the ecliptic, which is the Sun’s path across the sky. The Moon moves five degrees to either side of the ecliptic, allowing it to cover the bright star. And they’re going through a series of occultations now. Tonight’s event is the last one visible from the United States this year. Spica consists of two heavy stars that orbit each other once every four days. Occultations have helped astronomers decipher the system’s multiple personality, and learn some of its details. The main star, Spica A, is more than 11 times the mass and seven times the diameter of the Sun. Because it’s so massive, within a few million years the star will blast itself to bits as a supernova. Spica B is no slouch, either. But it’s not quite heavy enough to become a supernova. Instead, it will cast its outer layers into space more gently, leaving behind a small, hot corpse. Spica and the Moon climb into view just a couple of hours before dawn. The occultation will be visible across most of the country. The exact timing depends on your location. Script by Damond Benningfield

    2 min

  2. 2 DAYS AGO

    Big Families

    The Alpha Persei cluster is a family of more than 500 stars, spanning almost 150 light-years. All of the stars were born at the same time, from the same giant cloud of gas and dust. Tens of millions of years ago, the family was a lot bigger. Alpha Persei was one of several dozen clusters born in the same nursery. The clusters have all gone their own way. But a recent study supports the idea that they were born together. Astronomers used observations from the Gaia space telescope. It’s measuring the motions and other details of billions of stars. The astronomers looked at stars in more than 270 young clusters within a few thousand light-years of Earth. The observations allowed the researchers to “rewind” the motions of the clusters. They found that, about 30 million years ago, more than half of the clusters congregated in three “super” clusters. The groups are named for their brightest members – in this case, the Alpha Persei cluster. The scientists estimated that the three groups have spawned more than 200 massive stellar explosions. The supernovas carved bubbles and shells of gas that span hundreds or thousands of light-years. The Alpha Persei cluster is near the star Alpha Persei, the brightest star of Perseus. They’re in the northeast at nightfall. Under dark skies, the cluster is visible to the eye alone – a bright member of a scattered family of star clusters. Script by Damond Benningfield

    2 min

  3. 3 DAYS AGO

    Cosmic Ladder

    Before you climb a ladder, you want to make sure all of its rungs are secure. And astronomers try to do the same thing – with the cosmic distance ladder. It’s a series of techniques that reveal the distances to objects that are farther and farther away. For it to work, all the rungs have to be secure. One of the first rungs on the ladder uses a class of stars called Cepheid variables – big stars that are nearing the end of life. They’re unstable, so they pulse in and out. The length of the pulses and other details reveal a Cepheid’s true brightness. From that, you can calculate the star’s distance. For this step to work, astronomers need to know all they can about Cepheids. But that’s not easy. In fact, they’re still debating the details on the closest and most famous Cepheid: Polaris, the pole star, which stands due north. We do know that Polaris consists of at least three stars. The Cepheid is the one that we see with our eyes alone. It has a close companion. The third member of the system is quite a ways from the other two. The system appears to be about 450 light-years away. And a recent study says the Cepheid is about five times the mass of the Sun. Its surface has some big dark and bright spots. Their motion suggests the star rotates once every four months. Even those details aren’t certain. So astronomers still have to do a lot of checking to make sure one of the rungs of the cosmic ladder is secure. Script by Damond Benningfield

    2 min

  4. 4 DAYS AGO

    Expanding the Universe

    A hundred years ago today, the New York Times reported that Edwin Hubble had made a big discovery. He confirmed that many of the spiral objects known as nebulae were really separate galaxies – “island universes” of stars far outside the Milky Way. The story ran on page six, and it misspelled Hubble’s name. But it was the first public announcement of one of the greatest scientific findings of the 20th century. The discovery dramatically expanded the known universe. Instead of consisting of the Milky Way alone, the universe contained billions of galaxies, spread across billions of light-years of space. Hubble studied a class of stars in two spiral nebulae – Andromeda and M33. Called Cepheid variables, the stars pulse in and out. Measuring the length of its pulses and other details reveals the star’s true brightness. From that, astronomers can calculate the star’s distance. Hubble calculated that Andromeda was about 860,000 light-years away, and M33 a bit farther. Modern calculations show that they’re about three times farther than Hubble thought. Still, the concept was proved: the universe extends far beyond our galactic home – a concept revealed a century ago. Andromeda – now known as the Andromeda Galaxy – is in the east-northeast at nightfall. Under dark skies, it’s visible to the eye alone – 2.5 million light-years away. We’ll talk about the most famous Cepheid tomorrow. Script by Damond Benningfield

    2 min

  5. 5 DAYS AGO

    Whirling Dipper

    The stars of the Big Dipper dip quite low at nightfall at this time of year. In fact, from south of about Kansas City, one or more of its stars dip below the horizon and out of view. And from south of about Dallas, the entire dipper vanishes. Like all the stars north of the celestial equator, the stars of the dipper circle around the north celestial pole, which is marked by the star Polaris. How high or low the dipper stands depends on your latitude. From the northern half of the United States, the stars are “circumpolar.” That means they never set – they’re always above the horizon, both night and day. In many cultures, such stars were described as “eternal” or “undying.” That made them especially important in the skylore and mythology of those cultures. From the southern half of the country, the dipper isn’t circumpolar – not all of it, anyway. From some locations, one or two stars drop below the horizon. From others, the entire dipper sets. Even from those spots, though, it climbs back into view within a few hours. So the dipper is in sight for at least part of the night every night of the year. As twilight fades this evening, viewers at northern latitudes can see the dipper roughly parallel to the northern horizon. From southern latitudes, it might be hidden. But it will climb back into view after midnight. And no matter where you are, the Big Dipper will stand high in the sky at dawn. Script by Damond Benningfield

    2 min

  6. 6 DAYS AGO

    Moon and Regulus

    For the Moon, it’s another night, another bright companion. After passing close to the brightest star of Gemini and the planet Mars over the past couple of nights, tonight it takes aim at Regulus, the heart of the lion. The star climbs into good view directly below the Moon after midnight. The Moon will move toward the star during the night, so they’ll be much closer at dawn. The Moon passes near these bright lights because, just like the Moon, they all stay close to the ecliptic. That’s an invisible line that marks the Sun’s annual path across the sky. The stars all maintain a fixed position relative to the ecliptic – at least on human timescales. Over the millennia, the ecliptic itself actually shifts a little – the result of a slow wobble in Earth’s axis. The orbits of the Moon and planets are tilted a bit. That causes those bodies to move back and forth across the ecliptic. The planets cross the ecliptic every few months or years. But the Moon crosses every couple of weeks. It spends two weeks to the north of the ecliptic, then two weeks to the south of it. Tonight, it’s a few degrees to the north. Early Monday, though, it will cross to the southern side. And that will set up an especially close encounter with the next bright light along the ecliptic: Spica the brightest star of Virgo. In fact, the Moon will pass directly in front of the star early Wednesday. We’ll tell you all about that next week. Script by Damond Benningfield

    2 min

  7. 20 NOV

    Moon and Mars

    There’s no liquid water on the surface of Mars. But if you could squeeze the planet like a damp sponge, a lot of water might ooze out. Observations by a Mars lander suggest that huge amounts of water might lurk below the surface – enough to cover the entire planet with an ocean a mile deep. Mars was much warmer and wetter in the distant past. Rivers flowed across the surface, feeding into lakes and perhaps a giant ocean. Most of that water has vanished. There’s some frozen water in the polar ice caps and in slabs below the surface, but no liquid water. Scientists have been trying to figure out what happened to the rest of the water. Some of it was lost to space. But some could have trickled below the surface, in either liquid or frozen form. The InSight lander listened for “marsquakes” for four years. The way sound rumbles through the planet reveals details about what’s below the surface. A recent look at those observations suggested there could be a lot of water more than seven miles down. It would be contained in cracks and pores in volcanic rock – not as underground reservoirs. Still, it’s more than enough water to account for the ancient lakes and ocean – now hidden far below the Martian dunes. Look for Mars close to the upper right of the Moon as they climb into good view in late evening. The planet looks like a bright orange star. We’ll talk about the Moon and another bright light tomorrow. Script by Damond Benningfield

    2 min

  8. 19 NOV

    Moon and Pollux

    When astronomers compare the brightness of different stars, they use a scale known as absolute magnitude. That’s how bright the stars would look if they were lined up at the same distance: 10 parsecs, which is 32.6 light-years. One star they’d barely have to nudge is Pollux, the brightest star of Gemini. It’s only one light-year farther than that distance. So if it moved to exactly 10 parsecs, you’d have a hard time telling any difference in its appearance. That includes its color. Its orange glow tells us that its surface is thousands of degrees cooler than the surface of the Sun. Originally, Pollux would have shined almost pure white – an indication that its surface was much hotter than it is today. But the star used up the hydrogen fuel in its core. That triggered a series of changes that caused its outer layers to puff up to giant proportions. As the gas expanded, it cooled, making the star orange. Today, Pollux is the closest giant star to the Sun – a bit more than 10 parsecs away. Pollux is close to the Moon as they climb into good view by about 10 o’clock tonight. The moonlight will wash out some of the star’s color. Gemini’s other twin, the star Castor, will stand farther to the upper left of the Moon. They’ll be high in the sky at first light. By then, the Moon will line up half way between Pollux and an even brighter orange light: the planet Mars. We’ll have more about Mars and the Moon tomorrow. Script by Damond Benningfield

    2 min

  9. 18 NOV

    Storm Risks

    This has been a busy year for the Sun. It’s near the peak of its 11-year magnetic cycle, so it’s produced some big eruptions of energy and charged particles. Some of those outbursts have caused troubles here on Earth. And future storms could cause even bigger troubles, with some cities facing a greater threat than others. Solar outbursts are triggered by storms on the surface of the Sun. Lines of magnetic force become tangled and twisted. Eventually, they snap, then reconnect. That blasts energy and particles throughout the solar system. When these waves hit Earth, they can create brilliant auroras that appear much farther south than usual. On the downside, they can damage or destroy orbiting satellites, knock out some radio communications, and force airlines to reroute flights. And they can knock out power grids on the surface. An especially powerful storm could disrupt a grid for weeks. Scientists in Britain have been looking at the likelihood of such outages. They’ve considered many factors: the layout of power grids, how well the ground in a region conducts electricity, and how close to the surface auroras might come, among others. In the United States, the cities at greatest risk appear to be Milwaukee and Washington, D.C. The researchers are looking at those and other cities in more detail. That should allow them to come up with a better understanding of the risks we all face from our “stormy” star. Script by Damond Benningfield

    2 min

  10. 17 NOV

    Moon and Jupiter

    Jupiter is the “big brother” of the solar system in more ways than one. It’s more than twice as massive as all the other planets and moons combined. That makes its gravity especially strong, so it can push around the little guys. What’s more, Jupiter likely is the oldest of the Sun’s planets. Like all the planets, Jupiter probably was born from a disk of gas and dust around the young Sun. It began to grow in the cold outer regions of the solar system. Bits of ice, rock, and metal stuck together. By the time the Sun was perhaps one or two million years old, Jupiter had already grown to about 20 times the mass of the present-day Earth. Jupiter then began to gobble up vast amounts of gas. After another two or three million years, it was several dozen times Earth’s mass. It pulled in so much material that it cleared a wide gap in the disk around the Sun. And it blocked the stuff that was outside its orbit from drifting inward. That may have prevented the birth of anything more massive than Earth closer to the Sun. Earth, by the way, wasn’t born until the Sun was about 50 million years old – a younger brother to giant Jupiter. Look for Jupiter to the upper right of the Moon as they climb into view this evening. It looks like a brilliant star. The true star Aldebaran – the eye of the bull – is farther along that line. And fainter Elnath – the tip of the bull’s horn – is quite close above the Moon. Script by Damond Benningfield

    2 min
  • 10 Episodes

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 - 2024
  • Episodes
    10
  • Rating
    Clean
  • Copyright
    © 2022 The University of Texas McDonald Observatory
  • Show Website
    StarDate

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