StarDate Podcast show

StarDate Podcast

Summary: 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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 Desert Storm | File Type: audio/mpeg | Duration: 2:20

Back in late April, a meteor startled residents of California and Nevada when it exploded, showering the mountains with bits of rocky debris. But that’s not the first time that space rock has rained on the West. Another cosmic blast took place 100 years ago today. Around dinnertime on July 19th, 1912, several explosions rattled the desert town of Holbrook, Arizona. Minutes later, rocks fell from the sky — about 14,000 of them. They were the remains of a cosmic boulder that blew up as it slammed into the atmosphere. Thousands of bits of rock and metal pelt our planet every day. Most are no bigger than grains of sand, so they vaporize before they hit the ground. But a few of the bigger ones make it to the surface — either whole or in pieces. That’s what happened at Holbrook. The intense pressure generated by the boulder’s flight through the atmosphere caused it to shatter into thousands of pieces. When they hit the ground, such pieces are known as meteorites. The largest Holbrook meteorite weighs about 15 pounds. The smallest are tiny pebbles. In fact, a couple of decades after the incident, a scientist who visited the site found hundreds of these pebbles in anthills built by red ants. Coincidentally, Holbrook is only a few miles east of the site of yet another impact. A giant meteorite slammed into the landscape about 50,000 years ago, creating the most famous cosmic “scar” on Earth’s surface — the Arizona Meteor Crater. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Comet Swift-Tuttle | File Type: audio/mpeg | Duration: 2:20

Like football players and rocks stars, a comet can be famous one day and infamous the next. A case in point is Comet Swift-Tuttle. When it was discovered 150 years ago this week, comet discoveries were rare enough that the people who found them became instant celebrities. And by late in the year the comet was visible to the unaided eye, so it gained celebrity status for itself. That celebrity only grew years later, when it was discovered that the comet spawns the Perseid meteor shower, which peaks every August. Swift-Tuttle follows a long orbital path that takes it far from the Sun, so it spends decades in the outer solar system. That made it hard to determine its orbit. In fact, when the comet returned to view in the early 1990s — the first return since its Civil War appearance — astronomers thought there might be a problem — one that changed the comet’s reputation. Calculations showed there was a chance the comet could hit Earth in 2126. Swift-Tuttle is probably about 15 miles in diameter, so a strike would destroy much of the life on Earth. With a little more research, though, astronomers realized that the comet had been seen a couple of times in ancient China. Adding those appearances to the calculations showed that Swift-Tuttle will miss Earth by a few million miles. That’s close enough, though, for the comet to stage a spectacular display in the night sky — one that will take Swift-Tuttle back to the realm of the famous. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Tuttle Comets | File Type: audio/mpeg | Duration: 2:20

Not much could stop Horace Tuttle from searching for comets — not cold weather, international travel, or even the Civil War. In fact, about the only thing that slowed him down was himself. Tuttle began his quest for comets as an assistant astronomer at Harvard College Observatory in 1857. He found four comets in a little more than a year, and won a major international prize. And he discovered one his most famous comets 150 years ago this week. It’s called Swift-Tuttle after the two men who discovered it independently — Lewis Swift and Horace Tuttle. It’s the parent of the Perseid meteor shower in August. More about the comet tomorrow. When the Civil War started Tuttle joined the Army, then soon transferred to the Navy. He served with distinction on several ships — all while devoting many of his nights to the hunt for comets. He stayed with the Navy after the war, and was sent on several international expeditions. In 1875, though, Tuttle was accused of embezzlement. He’d been a Navy paymaster, and several years earlier his accounts had come up short. He wasn’t punished, though, until he tried to cash a large Navy check. He was court martialed, convicted, and given a dishonorable discharge. Within weeks, though, Tuttle was working for another government agency as a staff astronomer. And in 1884, he returned to the Navy — as an astronomer with the Naval Observatory. While there, he found one more comet — his last — in 1888. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Swift Comets | File Type: audio/mpeg | Duration: 2:20

To the people of Cortland, New York, Lewis Swift was a bit of an oddity. Most nights, for a little while after sunset and before sunrise, the hardware merchant used a small telescope to scan the skies close to the Sun. In 1862, though, his status changed from “oddity” to “celebrity.” On July 16th, Swift discovered a comet — one that went on to stage a great show. And today, the comet is better known as the parent of August’s Perseid meteor shower. Swift was born on Leap Day of 1820. At age 13, he fractured his hip in an accident, so for the next couple of years he devoted more time to study than farm work. In 1850 he developed an interest in microscopes. And a few years later, he built his first telescope. Swift became fascinated by comets after viewing a brilliant one in 1858, and making it the topic of his first scientific paper. When Swift first saw the comet of 1862, he wasn’t sure if it was new or one that had been seen before. A few days later, though, he heard that astronomer Horace Tuttle had reported the discovery of the same comet Swift had seen. Swift quickly reported his own observations, so the comet was named Swift-Tuttle in their honor. More about the comet tomorrow. After 1862, the comet disappeared from view for more than a century. Swift discovered several more comets, and eventually became a full-time astronomer, studying everything from eclipses to galaxies — a career built on the discovery of a comet. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Summer Delights | File Type: audio/mpeg | Duration: 2:20

The evening skies of summer are more thinly settled than those of winter — there are fewer bright stars to dazzle the eye. Even so, summer offers a few delights that are all its own. The two most prominent are the constellations Scorpius and Sagittarius, which scoot across the south during the night. Scorpius is due south as the sky gets good and dark. Under even moderately dark skies, it really does look like a scorpion, with a slightly curving body and a long tail with a nasty-looking “stinger” at the end. The scorpion is most easily identified by its bright “heart” — the star Antares. Its strong orange color will help you pick it out. The scorpion’s head extends to the upper right of Antares, with its tail to the lower left. Sagittarius stands farther to the left of Antares. But this constellation looks very little like its namesake, the archer — a centaur holding a bow. Instead, it’s best marked by a pattern of eight fairly bright stars that forms the outline of a teapot, with the handle to the left and the spout to the right. Under dark skies, you’ll see some “steam” rising from the spout — the hazy band of the Milky Way — the combined glow of millions of stars in the flat disk of our home galaxy. The center of the galaxy is hidden behind a dark cloud that interrupts the steam — a cloud of dust that absorbs the light of the stars beyond, blocking the view of what otherwise would be another treat for summer evenings. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 More Moon and Companions | File Type: audio/mpeg | Duration: 2:20

Dawn comes early on these summer mornings. Even so, it’s worth getting up a little early tomorrow to see a spectacular encounter involving the three brightest objects in the night sky: the Moon and the planets Venus and Jupiter. And to make the show even better, the “eye” of the bull looks on. The group rises a couple of hours before sunrise, and is in pretty good view by first light. Venus is the brilliant “morning star” below the Moon, with Jupiter above the Moon. The bull’s eye — the orange star Aldebaran — is just to the right of Venus. Through a small telescope, Venus looks like a miniature version of the crescent Moon. It looks that way for the same reason the Moon does — it’s roughly between Earth and the Sun, so most of the planet’s daytime hemisphere us facing away from us. Sunlight illuminates only a small fraction of the side that’s facing Earth. But while the Moon is moving back toward the Sun, Venus is moving away from the Sun as seen from Earth. So over the coming months, the fraction in sunlight will grow larger. At the same time, though, Venus will be moving farther from us, so it won’t be getting any brighter. In fact, Venus is actually at maximum brightness for its current morning appearance. For the rest of the year, it’ll slowly fade — although not by a whole lot. It’ll still reign as the “morning star” for the rest of the year. Tomorrow: bright delights in the evening sky. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Moon and Companions | File Type: audio/mpeg | Duration: 2:20

The “superstars” of the night sky share a tight stage before dawn the next few mornings: the Moon, the two brightest objects after the Moon, and the Pleiades star cluster. And the bright orange eye of Taurus is in the middle of things, too. At first light tomorrow, the Moon is well up in the east, with the Pleiades a little to its upper left. The cluster looks like a tiny dipper. If you look straight at it, it looks sort of hazy. But if you look through the corner of your eye, it’s easier to see the dipper’s individual stars. Most people see six stars with their eyes alone. But the Pleiades actually consists of hundreds of stars. It’s more than 400 light-years away, though, so most of the stars are much too faint to see without a telescope. Photographs of the Pleiades show wisps of blue around the stars, like a hazy veil. That glow comes from a giant cloud of gas and dust that’s passing by the Pleiades. Light from the cluster’s brightest stars reflects off the dust grains, forming the hazy nebula. Two brilliant points of light stand below the Moon — the planets Jupiter and Venus. Venus is the brighter of the two, and is lower in the sky. And the final member of this beautiful tableau is to the upper right of Venus: Aldebaran, the star that represents the eye of Taurus, the bull. On Sunday morning, the Moon will stand between Jupiter and Venus, creating an even tighter stage for these astronomical superstars. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Altairian Planets | File Type: audio/mpeg | Duration: 2:20

Science fiction loves the star Altair. Planets in the Altair system have been the setting for many novels, short stories, TV episodes, movies, and video games. In some of these stories, Earth wipes out the Altarians; in others, the Altarians wipe out Earth. The planets have been home to Earth colonies, an interstellar monetary system, and an interstellar junkyard. Perhaps the best-known of the bunch is the 1956 movie “Forbidden Planet,” in which a starship from Earth tries to rescue the survivors of an expedition from 20 years earlier. The survivors had found the remnants of an advanced race known as the Krell. But so far, all those planets are just fiction. Even though Altair is just 17 light-years away, astronomers haven’t discovered a single planet around the star. They have found that Altair contains a lot of heavy elements. That means the cloud of material that gave birth to Altair offered plenty of ingredients for planets. A lot of those ingredients are still there, in the form of dust grains around the star. Any planets that do orbit Altair are unlikely to host intelligent life — or perhaps any life. Altair is much younger than the Sun, so there’s been a lot less time for life to develop. So we’re not likely to find the remains of an ancient civilization like the Krell at this bright stellar neighbor. Look for Altair in the east as night falls. The bright white star forms the lower right corner of the giant Summer Triangle. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Altair | File Type: audio/mpeg | Duration: 2:20

The stars that dust the night sky are all moving around the center of the galaxy at hundreds of thousands of miles per hour. Yet they’re so far away that their motion is imperceptible across not just a human lifetime, but hundreds of lifetimes. In fact, even one of the fastest stars as seen from Earth will move just one degree over the next 5,000 years — less than the width of a finger held at arm’s length. Altair is the brightest star of Aquila, the eagle. In fact, the name “Altair” means “the flying eagle.” The star is in the east at nightfall, at the lower right corner of the bright, widespread Summer Triangle. Altair is only about 17 light-years away — closer than all but a handful of the stars that are visible to the unaided eye. That’s the main reason it’s moving in such a hurry. It’s like watching race cars on opposite sides of a track. Although the cars are all moving at about the same speed, those on the side closest to you cover a larger angle in the same amount of time than those on the far side. Yet that motion is too tiny to plot with the eye alone. Instead, astronomers make extremely precise measurements of its position against the background of more-distant stars. Comparing Altair’s position over a period of years reveals its apparent speed across the sky. Again, look for Altair almost due east at nightfall, climbing high across the south during the night, and almost due west at first light. More about Altair tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 More Vega | File Type: audio/mpeg | Duration: 2:20

The constellation Lyra, the harp, stands halfway up the eastern sky as night falls this evening, and climbs directly overhead around midnight. The little constellation is easy to locate because it contains one of the brightest stars visible from most of the northern hemisphere. Vega is on the northwest corner of the constellation, anchoring the widespread Summer Triangle. Vega is prominent not only in the sky — it’s prominent in skylore as well. Just about every major culture has woven legends and myths around the star. In ancient China, for example, Vega was known as zhi nu — the “weaving maiden.” Vega is part of the ninth lunar mansion — a slice of the sky that roughly corresponds to the distance the Moon travels across the starry background in a day. That mansion is known as niu lang — the “ox boy.” The ox boy also includes another member of the Summer Triangle — Altair, the brightest star of Aquila, the eagle. It’s well to the lower right of Vega at nightfall. The imaginary line that connects the two stars is seen as a bridge across the flowing band of the Milky Way, which is known in China as the celestial river. Look for the ox boy — the brilliant stars Vega and Altair — as they climb up the eastern sky this evening. And if you have a nice, dark sky, far from pesky city lights, you can also see the river of light between them: the hazy glow of the Milky Way. We’ll have more about the Summer Triangle tomorrow. Script by Robert Tindol, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Vega | File Type: audio/mpeg | Duration: 2:20

Most of us slow down a little as we age. And the same thing happens for stars — they spin more slowly as they get older. Compare, for example, the Sun and Vega, the brightest star of Lyra, the harp. The Sun is four-and-a-half billion years old, and it rotates about once a month. Vega’s about one-tenth of the Sun’s age, and it rotates twice a day. Like the Sun, Vega is near the middle of its life. It’s “fusing” the hydrogen atoms in its core to make helium. Vega’s more than twice as massive as the Sun, though, so it consumes that fuel much more quickly, which makes Vega thousands of degrees hotter than the Sun. Vega’s rapid rotation gives the star a pronounced “bulge” around the middle — it’s a lot bigger through the equator than through the poles. The Sun probably looked somewhat similar when it was young. Newborn stars tend to rotate quickly. Over time, though, they slow down. A star’s magnetic field acts as a brake, slowing the star as the magnetic field interacts with the planets, gas, and dust around it. Vega is surrounded by a pretty thick disk of dust, which may also contain planets, so it, too, is likely to slow down. Vega won’t live nearly as long as the Sun will, though, so it’ll still be spinning in a hurry as it nears the end of its life. Look for Vega high in the east at nightfall, and moving directly overhead later on. It’s one of the brightest stars in the entire night sky, so it’s hard to miss. More about Vega tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Summer Triangle | File Type: audio/mpeg | Duration: 2:20

As the color of twilight drains from the eastern sky this evening, a pyramid of bright stars fades into view: the Summer Triangle. It’s visible from just about anywhere — even light-polluted cities. The apex of the pyramid is marked by Vega, the leading light of Lyra, the harp. It’s about half-way up the eastern sky. It’s one of the brightest stars in all the night sky, so it’s hard to miss. Vega is classified as a “main-sequence” star — a star that’s in the prime of life. It’s steadily “burning” the hydrogen in its core to make helium. It’s a process that will continue for hundreds of millions of years. More about Vega tomorrow. The star that marks the lower right corner of the triangle is also on the main sequence: Altair, in Aquila, the eagle. It’s not quite as massive as Vega, though, so it doesn’t shine as brightly. The star at the opposite corner of the triangle has completed its time on the main sequence and has moved into the next phase of life — a supergiant. Deneb is no longer fusing hydrogen to make helium, but may be about ready to fuse the helium to make even heavier elements. The changes in its core have caused its outer layers to puff up, making the star about a hundred times wider than the Sun. And it’s also tens of thousands of times brighter than the Sun, so it’s easily visible even though it’s close to 1500 light-years away — about 60 times farther than Vega, and close to a hundred times farther than Altair. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 H-R Diagram | File Type: audio/mpeg | Duration: 2:20

Stars come in a bewildering array of sizes, colors, and temperatures. To sort out this diversity, astronomers use a powerful tool called the Hertzsprung-Russell diagram, which made its debut a century ago. The diagram takes its name from Danish scientist Ejnar Hertzsprung, who first published the diagram, in 1911; and American astronomer Henry Norris Russell, who, unaware of Hertzsprung’s work, produced a similar diagram two years later. The H-R diagram, as it’s known for short, plots a star’s luminosity — its true brightness — against its surface temperature. On this diagram, 95 percent of stars — including the Sun — fall into a band that slopes diagonally from hot, bright, blue stars like Regulus, to cool, dim, red stars like Proxima Centauri. This band is called the main sequence. Although main-sequence stars span a huge range, each generates energy the same way — by converting hydrogen to helium in its core. A second group of stars — the giants and supergiants — were once main-sequence stars, but they exhausted the fuel at their centers and puffed up to many times their original size. The third and final group is the dim white dwarfs. These are dead stars — former giants that shed their outer layers, leaving only their hot, dense cores. They form a group that’s below and parallel to the main sequence on the H-R diagram — a tool that depicts the lives of the stars. And we’ll talk about some examples of main-sequence and giant stars tomorrow. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Venus and Aldebaran | File Type: audio/mpeg | Duration: 2:20

We all know that those little twinkling lights in the night sky are stars — brilliant balls of hot gas seen from a great distance. Even so, it’s hard to comprehend just how far and how bright they really are. One way to get a handle on it is to compare a star to something that’s right next door. And there’s a good opportunity to do just that the next few mornings. The planet Venus is fairly low in the east at first light, shining as the brilliant “morning star.” The slightly fainter planet Jupiter is above it. But a true star is just below it — Aldebaran, the orange “eye” of Taurus, the bull. It doesn’t look as impressive as the two planets, but that’s only because of its great distance. Aldebaran is a stellar giant — it’s puffed up to many times the diameter of the Sun. That makes it exceptionally bright. To understand just how big and bright, compare it to Venus. Right now, the planet is about 38 million miles away. Aldebaran is 10 million times farther than that. If it were the same distance as Venus, it would span a third of the sky, and its surface would stretch halfway to Earth. Most impressive of all, Aldebaran would shine about a million million times brighter than Venus. Fortunately, we’ll never get that close to Aldebaran — all that energy would incinerate Earth. But in a few billion years, Earth will experience a similar view — as our own star, the Sun, swells to the same giant proportions as the bull’s bright orange eye. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

 Faint But Steady | File Type: audio/mpeg | Duration: 2:20

61 Cygni is one of our closest stellar neighbors — just 11 light-years away. And it consists of two stars, not one. Even so, it’s only barely visible to the unaided eye — a faint dot not far from the graceful outline of Cygnus, the swan. That’s because its two stars are only about half as massive as the Sun. But what the stars lack in flash, they’ll make up for in longevity — both will live much longer lives than the Sun. In fact, not a single star of that class has had time to die from old age. A star’s lifespan is determined by its mass. Heavier stars have more hydrogen to power their nuclear reactions, so you might expect them to live longer. But that’s just not the case. A massive star’s gravity is much stronger, so it squeezes the star’s core more tightly, making it much hotter. That revs up its nuclear reactions, so the star burns through its hydrogen fuel in a hurry. In fact, the heaviest stars live only a few million years. Lightweight stars aren’t squeezed as tightly, so they consume their fuel at a more leisurely pace. A star the mass of the Sun will “burn” its hydrogen for about 10 billion years. And a star that’s less than about three-quarters of the Sun’s mass will live several billion years longer. Since the universe is only 13.7 billion years old, that means that not a single one of these stars has had time to burn out on its own. Only interactions with other stars could snuff out such feeble cosmic lights. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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