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.

Épisodes

  1. -1 J

    Martian Clock

    Time is tricky. There’s no “universal” clock ticking along at a constant rate. Instead, every clock in the universe ticks at its own rate, influenced by its motion and by the gravity of the matter around it. Those influences are built into the clocks of GPS satellites; without them, the system would fail within days. Scientists recently calculated how clocks would tick on Mars – an average of 477 millionths of a second faster per day than clocks on Earth. But as Mars orbits the Sun, that rate varies by up to 226 millionths of a second. The scientists used Albert Einstein’s theories of gravity and motion. Stronger gravity and faster motion both make a clock move more slowly as seen by an outside observer. The surface gravity of Mars is only about a third as strong as Earth’s. And because the planet is farther from the Sun, it orbits the Sun more slowly. But Mars’s orbit is more lopsided than Earth’s, so its orbital speed varies more dramatically. The changing distance also alters the gravitational influence of the Sun, as well as that of Earth and the Moon. The researchers incorporated all of these variables – and many others – to figure out the ticking of Martian clocks. Mars is working its way into the morning sky. It’s quite low in the east during dawn twilight. But the planet will climb a little higher day by day, and will be in good view this summer. More about Mars tomorrow. Script by Damond Benningfield

    2 min

  2. -2 J

    Moon and Regulus

    The Moon creeps up on the heart of Leo tonight, the star Regulus. Regulus is close to the upper left of the Moon at nightfall. The Moon will move closer before they set, around 2 a.m. They’ll be closest together as seen from the West Coast. The star we see as Regulus is called Regulus A. It’s several times bigger and heavier than the Sun, and much brighter. A tiny companion star is so close that it’s impossible to see through the glare. That duo appears to have two more companions, Regulus B and C. They form their own pair, orbiting each other once every 600 years or so. Regulus B is about 80 percent the size and mass of the Sun, and one-third as bright. Regulus C is a third of the Sun’s mass and size, and just two percent as bright. Regulus B and C are 79 light-years from Earth – the same distance as Regulus A. And they’re moving through space in the same speed and direction as the brighter star. That suggests that they’re bound to Regulus A. But they’re a long way from it – several thousand times the distance between Earth and the Sun. So astronomers haven’t watched the system nearly long enough to calculate a mutual orbit for the two pairs of stars. Estimates say it would take more than a hundred-thousand years for them to complete one circuit. So it’s possible that they’re not really bound at all – just a chance alignment at the bright heart of the lion. Script by Damond Benningfield

    2 min

  3. -3 J

    Space Rescue

    A space telescope is scheduled for a rescue. If the plan works, a small spacecraft will boost it to a higher orbit. That would allow the telescope to keep watching the skies for years. Neil Gehrels Swift Observatory was launched in late 2004. It watches the universe at a wide range of wavelengths, from visible light to gamma rays – the most powerful form of energy. Its original mission was to study gamma-ray bursts – the explosive deaths of massive stars. They’re among the most violent events in the universe, and among the “swiftest” – they fade in as little as a few seconds. So the telescope has to pivot swiftly when a new burst occurs – hence its name. Swift’s original altitude was 375 miles. But the Sun has been especially active in recent years. It’s heated Earth’s atmosphere, causing it to expand. That’s dragged the telescope to less than 250 miles. There’s a good chance it could fall from orbit by the end of the year. The rescue mission is scheduled for launch within a few weeks. Swift wasn’t designed to be serviced in orbit, so it’ll take some delicate maneuvering to not harm its delicate equipment. The rescue ship will spend a couple of weeks flying around the observatory, giving controllers time to plot the capture. Once latched on, the craft will boost the telescope back to its original altitude – allowing it to keep watching some of the most powerful events in the universe. Script by Damond Benningfield

    2 min

  4. -4 J

    Moon and Gemini

    The Moon lines up with the twins of Gemini this evening – the stars Pollux and Castor. Pollux is the brighter twin, and is closer to the Moon. The brilliant planet Jupiter is to the lower right of the Moon. Gemini has been around for thousands of years. Its roots trace back to ancient Babylon, as do those of many other constellations. All of them were recorded in one of the most important works of astronomy in the ancient world. Known as the Almagest, it was written by Claudius Ptolemy around the year 150. Ptolemy studied many fields, including astronomy, astrology, geology, and music theory. The Almagest is perhaps his most famous work. In it, he recorded the positions of a thousand stars, and included details on the motions of the Sun, Moon, and planets. He also discussed everything from eclipses to the length of the year. The book listed 48 constellations that were visible from northern skies – Gemini among them. The constellations weren’t given any borders – just the regions of the sky in which they appeared. And some barren regions weren’t part of any constellation. Over the centuries, astronomers shifted things around some. And they created constellations for southern skies as well. Finally, in 1930, they created an “official” list of 88 constellations. Each one was given precise borders. That gave every star a home – its own “address” in the universe. Script by Damond Benningfield

    2 min

  5. -5 J

    Moon and Jupiter

    Hurricane season is whirling to life in the northern hemisphere. The giant storms twirl across the ocean, developing deadly winds, rains, and storm surges. As they grow, they trace a familiar pattern – cloud bands spinning counter-clockwise around the central eye. That spin is a result of the Coriolis effect. It’s caused by a combination of Earth’s rotation and its shape. Because Earth is a sphere, locations on the equator move more than 24,000 miles in 24 hours. Locations off the equator move a much smaller distance in the same time. So, as a storm moves across the northern hemisphere, its southern edge moves faster than its northern edge. This causes the storm to rotate counter-clockwise. The Coriolis effect is much more pronounced on the giant worlds of the outer solar system – especially Jupiter. It’s the biggest planet, and it has the fastest rotation – one turn in less than 10 hours. That combination deflects what normally would be north-south winds into east-west winds. They can blow at hundreds of miles per hour. They separate Jupiter’s atmosphere into wide bands. Individual storms – some the size of continents or bigger – spin through the bands, or along their boundaries – monster storms spinning through alien skies. Jupiter stands to the upper left of the Moon this evening. It looks like a brilliant star. The twins of Gemini are above the Moon, and we’ll have more about them tomorrow. Script by Damond Benningfield

    2 min

  6. -6 J

    Moon and Venus

    There’s a beautiful conjunction between the Moon and the planet Venus early this evening. Venus is the “evening star” – the brightest object in the night sky after the Moon. The Moon is a thin crescent – the Sun illuminates only a sliver of the lunar hemisphere that faces Earth. We can’t see it, but the Moon is moving farther from us – by about an inch and a half per year. It’s been moving away since it was born, when Earth was young. In fact, that shift was one of the clues that led to the leading theory of how the Moon was born. In the chaotic conditions of the early solar system, Earth was walloped by a planet about the size of Mars. That blasted debris into orbit around Earth. Much of that material quickly coalesced to form one or more moons. Today’s Moon is the only survivor. The collision caused Earth to spin much faster, so a day was much shorter than it is now. Gravitational interactions between Earth and Moon have slowed us down. But they’ve also caused the Moon to slide farther away. The process isn’t smooth – the Moon speeds up and slows down. And it won’t stay smooth in the future. Given enough time, the Earth-Moon system would reach a point when the same hemisphere of Earth would always face the Moon, and the Moon would stop moving away. But that time may never come. It could be so far in the future that the Sun will have expired – perhaps destroying Earth and its slip-sliding Moon. Script by Damond Benningfield

    2 min

  7. 17 MAI

    Hercules Cluster

    Many astronomical discoveries have come in stages – a series of “aha” moments where we learn more about the nature of an object. A good example is Messier 13, the Great Hercules Cluster. Under especially dark skies, it’s just visible to the unaided eye, so people have known about it forever. It looks like a faint, hazy star. But during the 1700s, the cluster was “discovered” several times. The first discovery was made by Edmond Halley. Using a small telescope, he came across it in 1714. He described it as “a little patch.” Charles Messier saw it a half-century later. He described it as “round, beautiful, and brilliant.” But, he wrote, “I am sure it doesn’t contain any star.” He made it the 13th object in his catalog. In 1779, though, William Herschel contradicted Messier. M13 “is a most beautiful cluster of stars,” he wrote. Many other discoveries have followed. They’ve told us that M13 contains hundreds of thousands of stars packed into a tight ball. And the cluster is ancient – 12 billion years old or older. Messier 13 is 25,000 light-years away. In early evening, look in the east-northeast for the Keystone of Hercules – a lopsided “square” of stars. M13 is between the two stars at the top of that pattern, a bit closer to the one on the left – a giant cluster that’s still producing amazing discoveries. Script by Damond Benningfield

    2 min

  8. 16 MAI

    Guitar Nebula

    Most of the stars in the Milky Way orbit the center of the galaxy in the same direction as all the other stars around them, and at about the same speed. But a few follow their own paths. An example is a star at the tip of the Guitar Nebula. The nebula is a bubble of gas with an outline that resembles a guitar. It’s in Cepheus, which is low in the north at nightfall. The king’s brightest stars form an outline that resembles a child’s drawing of a house. Don’t look for the nebula, though – it’s so faint that it wasn’t discovered until 1992. The guitar was sculpted by a pulsar – the crushed corpse of a mighty star. It spins once every two-thirds of a second, emitting a beam of energy that sweeps past Earth on each turn. The pulsar was born when the star exploded as a supernova. The explosion must have been off-center, so it gave the dead core a powerful kick. The pulsar is plowing through clouds of gas and dust at almost two million miles per hour. It leaves an expanding wake behind it, like a ship traveling across the ocean. That wake is what we see as the Guitar. But there’s more to the nebula than meets the eye. X-ray telescopes in space reveal a long, high-speed “jet.” It’s firing away from the tip of the nebula at a right angle to the nebula itself. The jet most likely is powered by the pulsar’s magnetic field, which funnels charged particles away from the pulsar – an interesting note from a celestial guitar. Script by Damond Benningfield

    2 min

  9. 15 MAI

    Starburst

    The Milky Way Galaxy is home to a few hundred billion stars. And on average, it gives birth to a couple of Sun’s-worth of stars every year. But a much smaller galaxy about 12 million light-years away puts the Milky Way to shame. It is spawning about 10 times as many stars per year. Like the Milky Way, Messier 82 is a thin disk, with spiral arms wrapping around a dense core. It’s less than half the size of the Milky Way. M82 is a starburst galaxy. It had a close encounter with another galaxy within the past hundred million years or so. That caused huge clouds of gas and dust to collapse, triggering the starbirth. The new stars are concentrated in the center of the galaxy, where astronomers have cataloged more than a hundred super star clusters. Each one contains hundreds of thousands of stars. Many of the stars are especially hot and massive, which makes the clusters especially bright. A strong “wind” of hot gas races away from that region. It squeezes the surrounding clouds, giving birth to more stars. But within another hundred million years, all the gas and dust will have been used up. Then, M82 will settle down to the same quiet life as the Milky Way. M82 is in Ursa Major. As night falls, it dangles below the upside-down bowl of the Big Dipper. It’s an easy target for small telescopes. We see it edge-on, so it looks like a small, bright slash. Script by Damond Benningfield

    2 min

  10. 14 MAI

    More Crux

    The brightest star of the Southern Cross is like a whole episode of “Dancing With the Stars.” It consists of perhaps six or more stars. They’re all twirling through their own ballroom, linked by the strong hands of gravity. Alpha Crucis is 320 light-years away. To the eye alone, it looks like a single point of light – the 13th-brightest star in the night sky. But binoculars or a telescope show two stars. Both of them are at least a dozen times as massive as the Sun, and thousands of times brighter. They’re so far apart that it takes about 1300 years for them to complete a single orbit around each other – a slow turn across the dance floor. But one of those stars is actually two stars on its own. They’re so close together that not even the biggest telescopes can see them individually – the second star reveals its presence only to special instruments. But it’s also bigger, heavier, and brighter than the Sun. The two stars are dancing to a faster tempo – one turn around each other every 76 days. Those three stars might have three more companions. They’re a long way from the first trio, and they’re not as impressive. But they appear to share a common motion through the galaxy with the brighter trio. That means the two groups could be gravitationally bound to one another – dancing a waltz that would require a hundred thousand years to complete one turn across the floor. Script by Damond Benningfield

    2 min
  • 10 épisodes

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À propos

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

Informations

  • Création
    Billy Henry
  • Années d’activité
    2017 - 2026
  • Épisodes
    10
  • Classification
    Tous publics
  • Copyright
    © 2022 The University of Texas McDonald Observatory
  • Site web de l’émission
    StarDate

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