StarDate

Billy Henry
  • 4.3 (6)
  • 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

    Rastaban

    The eyes of the dragon shine a third of the way up the northeastern sky at nightfall. Eltanin is the brightest star of Draco, with third-ranked Rastaban just above it. They circle high across the north during the night, and stand in the northwest at first light. Although Eltanin looks brighter than Rastaban, that’s only because of their different distances. Eltanin is about 150 light-years away, while Rastaban is at 380 light-years. So if you lined them up side by side, Rastaban would shine about twice as bright as the dragon’s other eye. Rastaban is only about 65 million years old, compared to four and a half billion years for the Sun. Yet it’s already passed the end of its “prime” lifetime. That’s because it’s about six times as heavy as the Sun. Such massive stars “burn” through their nuclear fuel at a frantic rate. So Rastaban has already converted the hydrogen in its core to helium. Now, it’s probably getting ready to ignite the helium to make carbon and oxygen. That’s caused the star to puff up – it’s about 40 times the diameter of the Sun. That’s the main reason it looks so bright – there’s a lot of surface area to beam light out into space. Eventually, the nuclear reactions in the core will stop. The star’s outer layers will blow out into space. That will leave only the dead core – a cosmic ember as heavy as the Sun but only as big as Earth – closing one of the dragon’s bright eyes. Script by Damond Benningfield

    2 min

  2. 2D AGO

    Dragon’s Eyes

    A pair of eyes stares down from the northeast as night falls now – the eyes of Draco, the dragon. They’re to the upper left of brilliant Vega, one of the night sky’s most prominent stars. The brighter eye is the star Eltanin, the dragon’s leading light. The name means “the serpent,” because the star once represented the entire dragon. Eltanin is an orange giant. It’s a good bit bigger, heavier, and brighter than the Sun. That makes it easy to see even though it’s more than 150 light-years away. The star should get a lot easier to see in the coming millennia. That’s because Eltanin and the Sun are moving closer together. In about one and a half million years, they’ll be at their closest – just 28 light-years apart. Assuming Eltanin hasn’t changed much by then, it’ll be the brightest star in the night sky – about as bright as the current champ, Sirius. The other eye, Rastaban, is just above Eltanin. Its name means “head of the serpent.” It’s more than twice as far as Eltanin. It, too, is a giant, but it’s much bigger and brighter – a thousand times as bright as the Sun. So it looks only a little fainter than Eltanin despite the extra distance. The rest of Draco curves to the left and above the dragon’s eyes, and curls around Polaris, the North Star. The eyes stare in the opposite direction – toward Hercules, who killed the dragon before both of them were placed in the heavens. Script by Damond Benningfield

    2 min

  3. 3D AGO

    Ghoul Duel

    Last July, space telescopes recorded an event that sounds like the plot of a “B” horror movie: Zombie Versus Vampire. Spoiler alert: the vampire won. It drained away the zombie’s life’s blood – or make that its after-life’s blood. The encounter took place in a galaxy billions of light-years from Earth. Space telescopes detected a sudden flare-up in X-rays from the galaxy’s outskirts. The region also produced several short outbursts of gamma rays, the most powerful form of energy. At their peak, each burst produced as much energy every second as the Sun will emit in a billion years. Analysis revealed a possible explanation: a medium-sized black hole devoured a white dwarf – the “corpse” of a Sun-like star. Astronomers have seen similar encounters before. But most of them involved stars that were in the prime of life, so the stars were big. A white dwarf is only about as big as Earth, which is just one percent the Sun’s diameter. So a white dwarf is compact and extremely dense. Its surface gravity is strong, so it’s not easily disrupted. In this case, though, the white dwarf buzzed a black hole about 75,000 times the mass of the Sun. The black hole’s gravity ripped apart the white dwarf in one big bite. Debris swirled around the black hole. Magnetic fields fired some of it into space at almost the speed of light, creating bursts of gamma rays. The whole thing was over in a flash – as the vampire sucked the zombie dry. Script by Damond Benningfield

    2 min

  4. 4D AGO

    No Boom

    A massive star in the Andromeda Galaxy might have tried to blow itself to bits, but it failed. Instead, almost the entire star collapsed to form a black hole about five times the mass of the Sun. Astronomers discovered the possible misfire while combing through observations by NeoWise, a space telescope that wrapped up its work a couple of years ago. They found an object that brightened dramatically at infrared wavelengths, which are invisible to the human eye, then slowly faded again. Earlier observations at visible wavelengths showed a supergiant star, perhaps a hundred thousand times as bright as the Sun. But as the infrared peaked and faded, the visible light faded completely – the star simply vanished. The astronomers concluded that the event was a failed supernova. The star stopped producing nuclear reactions in its core, so the core collapsed. A shockwave plowed through the star’s outer layers, blasting their gas outward. In most cases, such a shockwave creates a titanic explosion – a supernova. But this blast wasn’t powerful enough to overcome the core’s gravitational pull. So almost all the gas fell back onto the core, making it massive enough to form a black hole. A little material did escape. It formed a wide disk of gas and dust around the dying star. Energy from the star made it shine brightly in the infrared – a short flare-up that waned as the supergiant star collapsed and faded from sight. Script by Damond Benningfield

    2 min

  5. 5D AGO

    Ringing Down

    More than 1.1 billion years ago, a pair of black holes staged a violent merger. As they spiraled inward, the black holes produced an outburst of gravitational waves – “ripples” in spacetime that rang across the universe. Detectors on Earth “heard” those ripples in January of last year. In fact, it was the loudest and clearest detection of merging black holes to date. Analyzing the signal has told scientists quite a bit about black holes, and about the laws of gravity that govern them. The frequency and duration of the gravitational waves revealed details about the black holes. It showed that when they merged, each of them was spinning. And each was about 33 times the mass of the Sun. But the total mass after they merged was only about 62 times the Sun’s mass – less than the combined weight of the individual black holes. The rest of their mass was converted to energy – mainly the gravitational waves. The aftermath of the merger was important as well. The merged black hole vibrated like a ringing bell. As it settled down, the “ringing” faded away. How it faded matched predictions made by General Relativity – the theory of gravity introduced by Albert Einstein and refined by many others over the decades. It was the strongest evidence to date that General Relativity really is the rule that governs black holes – and sends gravitational waves rippling across the universe. Script by Damond Benningfield

    2 min

  6. 6D AGO

    Event Horizon

    For a trip that’s out of this universe, just cross the event horizon of a black hole. Nothing that passes through an event horizon can ever come back out, so we don’t really know what goes on inside a black hole. But we can be pretty sure that it’s like nothing else in the universe. A black hole’s mass is concentrated in a single point, called a singularity. Its gravity is infinitely strong. But as the distance from the singularity increases, its grip weakens. Eventually, it reaches a point where the escape velocity equals the speed of light – the event horizon. Since nothing can travel faster than light, anything that falls through the horizon is trapped. It may be doomed to merge with the singularity. So the event horizon acts like the “surface” of a black hole. But it’s not solid – there’s nothing to ram into. Instead, it’s more of a boundary between the black hole and anything outside it. The distance between the singularity and the event horizon marks the size of the black hole. And as more stuff falls in, the black hole gets bigger. A black hole that’s 10 times the mass of the Sun spans about 35 miles. The supermassive black hole at the heart of the Milky Way spans 13 million miles. And the heaviest black holes yet seen are more than 40 times the size of the orbit of Neptune, the Sun’s outermost major planet – a wide entrance to an out-of-this-universe experience. More about black holes tomorrow. Script by Damond Benningfield

    2 min

  7. MAY 4

    Eta Aquariid Meteors

    Comet Halley’s loss is Earth’s gain. As the comet orbits the Sun, it sheds a bit of ice and dirt from its surface. That debris spreads out along the comet’s path. Earth passes close to that path twice a year. Some of the solid particles ram into our planet, adding a minuscule amount to Earth’s mass. For skywatchers, the intersection creates two meteor showers, as the comet dust vaporizes in the atmosphere. And one of them is under way now: the Eta Aquariids. The shower’s peak lasts for several nights, centered around tomorrow night. At its best, the shower can produce a few dozen meteors per hour. Halley is a chunk of rock and ice about seven miles in diameter. On average, it orbits the Sun once every 76 years, although that period varies by a few years. It’s been recorded in Earth’s night sky for more than 2,000 years. Edmond Halley linked some of those appearances in 1705, demonstrating that a comet can return to view multiple times. Halley also predicted the comet’s next appearance, in 1758. When it showed up at the time he forecast, the comet was named in Halley’s honor. Over the centuries, the comet’s orbit moves away from Earth a bit. Today, we’re several million miles from that path. As the orbit shifts away, we pick up less and less of the comet dust. That makes the meteor showers less impressive. So over time, the Eta Aquariids will slowly die out. Script by Damond Benningfield

    2 min

  8. MAY 3

    Moon and Antares

    Antares has played a big role in the skylore of many cultures. And it’s not hard to understand why. It’s quite bright, it has a fiery orange color, and it’s near the ecliptic – the Sun’s path across the sky. The Moon and planets are close to the ecliptic as well, so they periodically swing past Antares. In fact, the Moon snuggles quite close to it late tonight. In western skylore, Antares represented the heart of Scorpius, the scorpion. After Orion the hunter bragged that he could kill any beastie on Earth, the angry gods sent the scorpion to sting him to death. They then put Orion and the scorpion on opposite sides of the heavens, so one rises as the other sets. Antares and the surrounding stars also represented a scorpion in the mythology of the Maya and several other cultures. But others saw Antares differently. In China, it was the “fire star” – a description of its color. It and a couple of nearby stars represented the heart of a dragon. And in Hawaii, Antares was part of a fishhook used by the god Maui. The star itself is worthy of its reputation. It’s a dozen or more times heavier than the Sun, hundreds of times wider, and tens of thousands of times brighter – a supergiant star with some supergiant stories. Antares is just a skosh away from the Moon as they climb into good view tonight, by midnight. They’ll still be close as dawn twilight erases the scorpion’s mighty heart from view. Script by Damond Benningfield

    2 min

  9. MAY 2

    Degenerate Future

    The Sun faces a “degenerate” future. That’s not a value judgment – it’s physics. When the Sun can no longer produce nuclear reactions, its core will collapse. How far it collapses is limited by a type of pressure exerted by its atoms – degeneracy pressure. Today, the Sun is “fusing” atoms of hydrogen to make helium. When the hydrogen is gone, it’ll fuse the helium to make carbon and oxygen. But the Sun isn’t massive enough to extend that process, so its nuclear furnace will be extinguished. Fusion releases energy, which balances the pull of gravity. That keeps the Sun puffed up. Right now, it’s big enough to hold a million Earths. When fusion stops, gravity will win out. The core will shrink to the size of Earth itself. But it’ll still be about half as heavy as the present-day Sun. So a chunk the size of a sugar cube would weigh a ton. The dead core won’t shrink beyond that. That’s because the electrons in the core will exert their own pressure – degeneracy pressure. They can be squeezed only so much before they run out of “elbow room” and halt the collapse. That will leave a white dwarf – a dead cosmic cinder – to cool and fade over the eons. The galaxy is littered with white dwarfs, but none of them is bright enough to see with the eye alone. The closest one is a companion of Sirius, the brightest star in the night sky, which is low in the southwest as night falls – a star that faces its own “degenerate” future. Script by Damond Benningfield

    2 min

  10. MAY 1

    May Day

    For centuries, the people of the British Isles marked the beginning of summer not on the solstice, in June, but on May 1st. It’s a cross-quarter day, which comes about half way between a solstice and an equinox. In Scotland and Ireland, the date was known as Beltane. People built bonfires to celebrate the longer days, and held rituals to protect their crops and livestock. And in England, the date became known as May Day. People celebrated with village fetes, and they danced around the maypole. Dancers grabbed ribbons attached to the top of the pole, then circled around it, getting closer with each circuit. Especially tall maypoles were erected in an area of London known as the Strand. The last of these poles was removed 300 years ago. But it found a new life – supporting one of the world’s largest telescopes. The maypole was acquired by Isaac Newton, who had formulated laws of gravity and motion. In April of 1718, he had the pole moved to a park outside London for use by James Pound, an astronomer and clergyman. Pound had the use of a large lens created by another astronomer. The telescope was created by mounting the lens on the maypole. The eyepiece was on the ground, linked to the lens by a long wire. With that telescope, Pound measured the positions of the moons of Jupiter and Saturn. Newton used those observations to calculate the moons’ orbits – measuring a celestial dance around the maypole. Script by Damond Benningfield

    2 min
  • 10 Episodes

Hosts & Guests

Ratings & Reviews

4.3
out of 5
6 Ratings

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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