StarDate Podcast
By McDonald Observatory
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Podcast Description
StarDate, the longest-running national radio science feature in the United States, tells listeners what to look for in the night sky, and explains the science, history, and skylore behind these objects. It also keeps listeners up to date on the latest research findings and space missions. And it offers tidbits on astronomy in the arts and popular culture, providing ways for people with many diverse interests to keep up with the universe.
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The Keystone | You can never judge a star by its appearance alone. The four stars at the center of Hercules, for example, all look pretty much alike. But each has its own story that’s different from all the others. The stars form a sort of lopsided square called the Keystone. It’s well up in the east at nightfall. Its brightest star, at the upper right, is Zeta Herculis. Moving clockwise, the other three are Epsilon, Pi, and Eta Herculis. Zeta is the closest of the four, at a distance of just 35 light-years. It actually consists of two stars. One of them is bigger, heavier, and brighter than the Sun, while the other is smaller, lighter, and fainter. The larger one is nearing the end of its life, so it’s undergoing some changes that have caused it to puff up and shine brighter. Epsilon is also a binary, although both of its stars are more impressive than the Sun. But like the Sun, they’re both in the stellar equivalent of middle age, steadily “burning” through the hydrogen in their cores. Pi is the most impressive member of the Keystone. It’s about 370 light-years away — more than 10 times farther than Zeta. It’s so large that it would just about fill the orbit of Mercury, the closest planet to the Sun. And even though it’s just a small fraction of the Sun’s age, it won’t live much longer. And finally, Eta is also more impressive than the Sun. And it, too, is nearing the end of its life — a stage the Sun won’t enter for billions of years. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/24/12 | Free | View In iTunes |
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Hercules Cloud | As a boat glides along the surface of a lake, it creates a wake — small waves that ripple outward. The waves can push debris away from the boat’s path, concentrating the debris in a fairly small area. The same thing can happen with the stars. In fact, the motion of a giant bar of stars in the middle of the Milky Way galaxy seems to have forced millions of stars to congregate in a giant cloud. It’s known as the Hercules Cloud because many of the stars appear within the borders of the constellation Hercules. The cloud was discovered more than a decade ago as an unusually tight grouping of stars centered about 10,000 light-years away. As astronomers studied the region in detail, they discovered that the cloud contains millions or even hundreds of millions of stars, and it’s thousands of light-years long. It’s well above the plane of the Milky Way’s broad, flat disk, in a region that contains mainly older stars. The motions of the stars suggest that the cloud formed in the wake of the Milky Way’s central bar — a brick-shaped region of billions of stars that rotates like a big propeller. The gravity of the passing bar collected and concentrated the stars above it — forming the Hercules Cloud in its wake. The stars in the Cloud are too faint to see without a telescope, but Hercules itself is in the east as night falls. It’s marked by a lopsided square of moderately bright stars known as the Keystone. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/23/12 | Free | View In iTunes |
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Hercules Cluster | An ancient “city” of stars passes high overhead on spring and summer evenings — a globular cluster known as the Hercules Cluster, M13. It’s a faint, fuzzy point of light in the constellation Hercules. The cluster is about 25,000 light-years away, and it contains hundreds of thousands of stars. But they’re crammed into a region that’s only about a hundred light-years across, so the cluster contains hundreds of times more stars than are found in a similar volume of space around the Sun. Most of the stars in globular clusters are red and faint — a strong indication that they’re among the galaxy’s oldest stars. In fact, the stars in M13 are probably at least 12 billion years old — close to three times the age of the Sun. The stars in globulars are also different from the Sun in another way: They contain far fewer heavy elements. The Big Bang created lots of hydrogen and helium, but almost nothing heavier than those simple elements. Everything else — from carbon and oxygen to gold and uranium — was forged in the hearts of stars. As stars die, they expel some of these elements into space, where they can be incorporated into new stars — like the Sun. But the stars of M13 were born before most of the heavy elements found in the universe today were formed. So almost all of the heavy elements they contain are elements that the stars of M13 created on their own — elements forged over the last 12 billion years. More about Hercules tomorrow. Script by Damond Benningfield, Copyright 2003, 2008, 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/22/12 | Free | View In iTunes |
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Hercules | One of the most famous characters in the night sky takes a prominent position at this time of year — Hercules, the strongman. His relatively faint constellation is in view by the time it gets dark, and soars high overhead during the night. Hercules is the Roman version of a character from Greek mythology. He was the son of Zeus, the king of the gods, and a mortal woman. To appease his wife, who was angry at Zeus’s dalliance, Zeus named the boy Heracles, which means “glory to Hera.” But the strategy didn’t work. Hera tormented Hercules throughout his life. He was forced to perform 12 labors of strength and courage to atone for crimes he committed while under the spell of Hera. His labors included killing a lion and a snake, which also stand in the stars. The most prominent portion of the constellation Hercules is the Keystone — four stars that form a lopsided square. It’s above the northeastern horizon as darkness falls. Along the line connecting the two stars that rise first, look for a beautiful globular star cluster known as M13. In dark skies, it’s visible to the unaided eye as a faint smudge of light. Binoculars reveal a swarm of stars, while telescopes reveal hundreds of them. In fact, M13 contains hundreds of thousands of stars packed into a tight ball. These stars are among the oldest in the galaxy. More about M13 tomorrow. Look for Hercules ascending the sky beginning at nightfall, and soaring high overhead after midnight. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/21/12 | Free | View In iTunes |
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Moon and Venus | The crescent Moon and the planet Venus stage a beautiful display the next few evenings. Tonight, the Moon is quite low in the sky at sunset, with brilliant Venus well above it. The Moon sets by the time the sky gets fully dark, so you need to look quickly to see it. Venus is getting ready to disappear from view soon, too. It’s dropping noticeably lower in the sky day by day, and by month’s end, it’ll be so near the Sun that it’ll be almost impossible to see. The planet is nearing a point in its orbit known as inferior conjunction, when it crosses between Earth and the Sun. It’ll be closest to Earth then, at a distance of about 26 million miles. After that, it’ll quickly climb into view in the morning sky. Venus’s orbit is aligned in such a way that it usually passes a little above or below the Sun as seen from Earth. This time, however, it will pass directly across the face of the Sun, forming a tiny, dark silhouette — an event known as a transit. That will take place on the afternoon of June 5th for those of us in the United States, and at least part of it will be visible across the entire country. We’ll have much more about the transit as the date gets closer. In the meantime, enjoy the view of the brilliant “evening star” as it heads toward its encounter with the Sun. Venus is high above the Moon this evening, close to its upper right tomorrow evening, and far to its lower right on Wednesday. Tomorrow: the strongman. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/20/12 | Free | View In iTunes |
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Annular Eclipse II | Most of the United States will see a rare astronomical alignment late today: a partial solar eclipse. And across a narrow swath of the western U.S., the eclipse will be even rarer — the Moon will be completely enfolded within the Sun’s disk, leaving a thin but bright ring of sunshine around the Moon. A similar eclipse took place on May 10th, 1994, although this one is shifted about a third of the way westward around the globe. And in fact, the two eclipses are like cousins — both are members of an eclipse “family,” known as a Saros. We’re all familiar with the Moon’s month-long cycle of phases. But the Moon also has other cycles — its distance from Earth and its relation to the Sun’s path across the sky, among others. Three of these cycles overlap every 6,585-and-a-third days — a bit more than 18 years. When they overlap, there’s an eclipse. Each Saros cycle lasts for centuries. It begins with partial eclipses that are visible from one of the poles, then moves across Earth’s disk with total or annular eclipses, then finishes with more partial eclipses at the opposite pole. Today’s eclipse is part of Saros cycle 128. The first eclipse in the series took place in the year 984, and the last will be in 2282. The annular part of today’s eclipse begins around 6:24 p.m. Pacific Time, at the California-Oregon border. It ends at 8:39 p.m. Central Time, as the Sun and Moon set over western Texas. Script by Damond Benningfield, Copyright 2012 More about the eclipse For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/19/12 | Free | View In iTunes |
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Annular Eclipse | The Sun and Moon will team up to produce a brilliant ring of fire across the western United States tomorrow afternoon — an annular solar eclipse. The eclipse occurs because the Moon will pass directly between Earth and Sun, covering the Sun’s disk. But the Moon is near its farthest point from Earth, so it won’t be quite big enough to cover the entire disk. Instead, a thin ring of sunlight will encircle the Moon. The annular eclipse will be visible across a narrow strip of Earth’s surface that begins in China, wraps across the Pacific Ocean, and ends in the western United States. From the U.S., the path of the eclipse begins at the California-Oregon border around 6:24 p.m. Pacific Time. It then sweeps to the east-southeast, ending over western Texas when the Sun and Moon set at 8:39 p.m. Central Time. The annular portion of the eclipse will last up to about five minutes. Most of the rest of the United States will see a partial eclipse — the Moon will cover a fraction of the Sun, but it won’t be completely enfolded within the Sun’s disk. One note of caution, though. While the Moon will hide most of the Sun’s disk, the visible ring is still bright enough to cause eye damage. To view the eclipse, look through dark welder’s glass, or build a “projector” by poking a pinhole in the side of a cardboard box and watching the sunlight projected inside the box — the progress of a solar eclipse. We’ll have more about the eclipse tomorrow. Script by Damond Benningfield, Copyright 2012 More about the eclipse For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/18/12 | Free | View In iTunes |
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Happy Coincidence | A solar eclipse is a happy scientific coincidence. As seen from Earth, the Moon and Sun are the same size in the sky. So when the geometry is right, the Moon can cover up all or most of the Sun’s disk. An eclipse of the “most” variety is coming up on Sunday afternoon for parts of the western United States. It’s called an “annular” eclipse because the Moon won’t cover up all of the Sun. Instead, it’ll leave a thin but bright ring of sunlight around the Moon. Solar eclipses occur when the new Moon crosses directly between Sun and Earth. They don’t happen at every new Moon, though, because the Moon’s orbit around Earth is tilted with respect to Earth’s orbit around the Sun. So most months, the Moon passes a little above or below the Sun as seen from Earth. But two or three times a year, on average, the geometry is just right, creating an eclipse. Sometimes it’s total, sometimes it’s annular, and sometimes it’s just partial — the Moon obscures only a part of the Sun’s disk. The “coincidence” part comes in because of the relative sizes of the Moon and Sun in the sky. The Sun is 400 times wider than the Moon, but it’s also 400 times farther, so they take up the same amount of sky. The Moon is moving farther from Earth, though — at about an inch-and-a-half a year. So in a few hundred million years the Moon will be too far away to ever completely cover the Sun — and the spectacle of a total solar eclipse will disappear. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/17/12 | Free | View In iTunes |
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Clockwork Eclipses | A solar eclipse is coming up on Sunday afternoon and evening for most of us in the United States. Most will see a partial eclipse, with the Moon covering up only a portion of the Sun’s disk. But across a 200-mile-wide path from California to Texas, the Moon will fit inside the solar disk, surrounding the dark Moon with a ring of fire — a configuration known as an annular eclipse. The timing of the eclipse is known down to the second. In fact, the motions of Earth, Moon, and Sun are so well understood that astronomers have already prepared equally precise timings of eclipses that won’t take place for centuries. Such precise timing hasn’t always been the case, though. In fact, an eclipse forecast made 250 years ago helped turn a French astronomer into the toast of French science and society. Madame Nicole-Reine Lepaute was the court astronomer to King Louis XV. In 1762, she wrote a paper predicting the circumstances of an eclipse that would be visible from Paris two years later. Her predictions were right on target. Her husband, the king’s clockmaker, built a special clock to celebrate her accomplishment. It included a diagram of the eclipse from her paper, plus a small figure of Urania, the muse of astronomy. The clock is still around today — not in Paris, but on the campus of the University of Arizona — marking the never-ending motions of Earth around the Sun. We’ll have more about Sunday’s eclipse tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/16/12 | Free | View In iTunes |
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Going Solar | WHEELWRIGHT: My name is Brian Wheelright, I am a PhD student in optical sciences at the University of Arizona, and I work at the Steward Observatory Mirror Lab. And what we’re looking at today is part of our solar lab, where were trying to get solar energy to be cheap and competitive with fossil fuels. For three decades, the Steward mirror lab has been making some of the world’s largest telescope mirrors. Early this year, for example, it was working on four mirrors that, if turned on edge, would each be taller than a two-story building. It’s an enterprise that requires a lot of time, money, and expertise. A few years ago, lab founder Roger Angel began turning that expertise to a new project: developing a cheaper way to generate solar power. Technicians heat panes of ordinary window glass until they get soft, then mold them to a curved shape. They then mount the panes on a test stand in an abandoned swimming pool on the University of Arizona campus. The glass reflects sunlight into a special collector — a combination of lenses and solar cells that’s more efficient than most solar power systems today. The rig borrows from techniques used to build telescopes — but with some differences. WHEELWRIGHT: In telescope tracking, you have to be precise, and so it’s very expensive. Here, we just want it strong enough so that it survives the wind, but not so strong that it becomes expensive. Kind of a Sun telescope — an energy telescope is what they used to call this. A larger test project is under construction. Like all telescopes, it’s designed to capture the light of a star — in this case our own star: the Sun. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/15/12 | Free | View In iTunes |
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Making Mirrors | BRASS: We build mirrors 8.4 meters or 6.5, and our first step is to put down silicon carbide floor plates. Beneath Arizona Stadium in Tucson, four giant slabs of glass are taking shape — the mirrors of future telescopes. Placed on edge, each mirror is taller than a two-story building, and its surface is as roomy as a small apartment. Yet each is relatively thin and lightweight. The mirrors are produced by the Steward Mirror Laboratory at the University of Arizona. They’re the largest single-glass telescope mirrors yet built. They start with 20 tons of raw glass that’s melted inside a spinning oven. From inside the busy lab, Alan Brass explains: BRASS: We've got 20 tons of glass loaded in, put the cover to the furnace on, start it spinning, and it takes about a week to get up to temperature. At 2130 degrees the glass fully is the consistency of honey... As it spins, the glass forms the curvature needed to bring starlight to a sharp focus. After the mirror is cast, it cools for several months. Then its surface is ground and polished to a precise shape. After that, it’s tested to make sure it has the right shape — a flaw of a thousandth of the width of a human hair would spoil the view. Finally, it’s packed and shipped to its destination — an astronomical observatory. After final assembly and testing, it’ll get to work — uncovering the secrets of the universe. More about the mirror lab tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/14/12 | Free | View In iTunes |
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Giant Magellan Telescope | The last two decades have been a Golden Age for astronomy. A score of giant new telescopes has started scanning the skies, helping astronomers answer some old questions, and ask a lot more new ones. With these instruments, astronomers have studied dark matter and dark energy; discovered or confirmed hundreds of planets in other star systems; and even watched the weather on the outer planets of our own solar system. Yet an even brighter age may be ahead, as astronomers prepare the next generation of giant telescopes. One of the biggest is GMT — the Giant Magellan Telescope. It’s being planned and built by a consortium of universities, including the University of Texas at Austin. The telescope’s primary mirror, which gathers starlight, will consist of seven individual segments, each of which is as big as the largest single mirrors made so far; more about that tomorrow. Combined, the mirrors will give GMT five times the area of the largest telescopes in use today. And the telescope will be built on a mountaintop in Chile, in one of the driest climates on Earth — a perfect spot for skywatching. With GMT, astronomers expect to not just find planets in other systems, but actually see them. They’ll also use the telescope to look at the dawn of the universe, allowing them to see the formation of the first galaxies. And they’ll make discoveries that today they can’t even predict — part of the age of jumbo telescopes. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/13/12 | Free | View In iTunes |
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Primordial Clouds | The Big Bang forged only three elements — hydrogen, helium, and a little bit of lithium — the lightest and simplest elements of all. Stars formed from these elements, and converted some of them into heavier elements, such as carbon, oxygen, and iron. Astronomers have searched in vain for a star or gas cloud made solely of the three elements from the Big Bang — they all contain at least a small amount of heavier material. But they recently discovered two gas clouds that seem to be primordial — they contain no detectable heavy elements at all. One cloud is in Leo, the lion, while the other’s in Ursa Major, the great bear. The clouds are more than 11 billion light-years away, so we see them as they were only about two billion years after the Big Bang. Both clouds are dark. Astronomers found them only because the clouds happen to lie in front of even more distant quasars — extremely bright galaxies that were common in the early universe. Different elements in the gas clouds reveal their presence by absorbing light from the quasars. But the only element that could be seen was hydrogen, which was made in the Big Bang. From this, the astronomers deduce that the clouds have no more than about one ten-thousandth as much heavy elements as the Sun does. The discovery indicates that even two billion years after the Big Bang, some regions remained pristine — their composition unaltered from the time of the birth of the universe. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/12/12 | Free | View In iTunes |
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Serpens | The head of the serpent is slithering into the evening sky this month, with its tail twisting along a bit later. Serpens is the only constellation that’s split apart. The two halves are separated by Ophiuchus, the serpent bearer. The snake’s head is to the west of Ophiuchus, so it rises first. It’s low in the east as night falls, marked by a serpentine trail of faint stars. The tail, which is to the east of Ophiuchus, follows a couple of hours later. The brightest of the snake’s stars is Unukalhai — an Arabic name that means “the serpent’s neck.” It’s also known as Alpha Serpentis, indicating its ranking as the constellation’s leading light. The star is in the final stages of life. It converted the hydrogen fuel in its core to helium, causing the core to shrink and get hotter. That triggered the next round of nuclear reactions, with the helium being converted to carbon and oxygen. The changes in the core have also caused the thick layers of gas around the core to puff up like a balloon, making the star about 15 times wider than the Sun. They’ve also made the star’s surface much cooler, so it shines yellow-orange. In time, all the reactions in the star’s core will stop, and the outer layers will puff out into space. For awhile, that expanding cloud will form a colorful bubble in space. As the bubble cools and dissipates, though, only the star’s dead core will remain — depriving the serpent of its leading light. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/11/12 | Free | View In iTunes |
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Wobbly Clocks | Pulsars are some of the most bizarre objects in the universe. And an experiment that’s being developed now may allow scientists to use pulsars to confirm a prediction in Albert Einstein’s theory of gravity. A pulsar is the tiny, ultradense core of a dead star. Some pulsars spin up to hundreds of times per second, beaming energy into space like a cosmic lighthouse. The timing of these “pulses” of energy is so precise that pulsars are some of the best clocks in the universe. And astronomers may be able to use those clocks to detect something predicted in Einstein’s equations: gravitational waves. Richard Price of the University of Texas at Brownsville explains: PRICE: We can detect these pulsars as if they were perfect clocks fixed at a point in the universe. When we see some sort of variability in that timing, we can, in principle, infer that that variability is due to the passage of a gravitational wave between us and the pulsar. Gravitational waves are “ripples” in spacetime caused by the motions of massive objects. There’s evidence that they exist, but no proof. As they move through space, they change the distances between objects by a tiny amount. The pulsar experiment is designed to detect very long waves, which should be produced by monster black holes in distant orbits around each other. Such waves may also be left over from the Big Bang. If the experiment works, it would provide one more confirmation of Albert Einstein’s theory of gravity. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/10/12 | Free | View In iTunes |
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Gravity Probe B | As Earth turns, it drags us and everything else on the surface along with it — a result of the planet’s gravitational pull. And it drags something else, too: space itself — an effect that was confirmed just last year. Albert Einstein’s theory of gravity, known as General Relativity, says that massive bodies “warp” the space around them. For something as small and light as Earth, the effect is tiny. It’s more pronounced around more-massive objects, like stars, so it’s easier to detect. Relativity also predicts that if a massive object is rotating, the warp in space rotates, too — the object actually drags space along with it. A satellite launched in 2004, called Gravity Probe B, spent a year measuring the effect of Earth’s gravity on space. It did so with a set of ultra-precise gyroscopes, which were deflected by Earth’s pull on the space around it. After that, it took scientists five years to fully analyze the data. They announced their results last May: Earth does indeed drag the space around it — by exactly the amount predicted by Einstein’s equations. And as with the warp in space, the dragging effect is much stronger around objects that are heavier and denser than Earth. In fact, the densest objects of all — black holes — may drag space at a good fraction of the speed of light — a gravitational maelstrom explained by Albert Einstein. We’ll talk about another test of Einstein’s theory of gravity tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/9/12 | Free | View In iTunes |
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Luna See | The Moon stands due south at first light tomorrow. The portion that’s illuminated by sunlight includes an area of bright, jumbled terrain known as the southern highlands. That region was the first target for an experiment that began 50 years ago tonight — an experiment that helped set up a test of Albert Einstein’s theory of gravity that continues today. The experiment was called Luna See. Scientists and engineers from MIT aimed a red laser at the lunar surface. Over three nights, they fired the laser 80 times, and used a telescope to measure its reflection. The experiment didn’t provide much scientific return, but it did show that you could bounce a laser off the Moon. And that set up an experiment that’s still running. Apollo astronauts and unmanned Soviet rovers left special reflectors on the Moon to bounce lasers back to Earth more efficiently than by using the Moon itself. And scientists have been using those reflectors ever since. Among other things, their work has helped probe the Moon’s interior and measured how quickly the Moon is moving away from Earth. The work has also provided a test of Einstein’s theory of gravity, General Relativity, by measuring the motions of Earth and the Moon around the Sun. So far, the experiment has confirmed Einstein’s equations. But today they’re using bigger telescopes and a more powerful laser to continue the experiment — providing an even better test of General Relativity. More tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/8/12 | Free | View In iTunes |
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Relativity and GPS | [SFX: GPS device sounds] The Global Positioning System is one of the marvels of modern technology. It guides us on land, in the air, and at sea. It helps rescuers find lost hikers. And it makes it possible for most of the world to track your every move. Yet without the contributions of Albert Einstein, GPS wouldn’t work at all. The system consists of a network of satellites in Earth orbit. Each satellite has an atomic clock that’s accurate to a few billionths of a second. GPS receivers determine your position by triangulating the time signals from several satellites, providing an accuracy of a few feet. But each satellite is moving at thousands of miles an hour. And it’s thousands of miles high, so it “feels” a weaker gravitational pull than at Earth’s surface. According to Einstein’s theories of Relativity, those effects mean that the clocks on the satellites tick faster than those on the ground — by about 38 millionths of a second per day. That may not sound like much, but for a system in which billionths of a second matter, it’s huge. Over a single day, that would add up to a positioning error of several miles. So before the satellites are launched, their clocks are adjusted so that they tick slightly slower than they would on Earth. That keeps their timing just right — and keeps you on target. More tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/7/12 | Free | View In iTunes |
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General Relativity | When it comes to describing gravity, Albert Einstein is the heavyweight champ. So far, every test has confirmed his theory of gravity, which is known as General Relativity. Published more than a century ago, the theory said that gravity wasn’t a “force” acting instantly across the universe, as Isaac Newton had envisioned it. Instead, any object with mass — from a pill bug to a galaxy — “warped” the spacetime around it. A pill bug’s effect is negligible, but the effect of more massive objects could be profound. A star, for example, should curve space in such a way that it would deflect the light of more-distant stars passing by it. This effect was confirmed during a solar eclipse in 1919. That made Einstein an international star — and put him at the pinnacle of gravitational theory. Since then, General Relativity has been confirmed in many other ways. One of the first was a small shift in Mercury’s orbit around the Sun — it’s caused by the Sun warping the space around it. General Relativity also predicts a gravitational redshift, in which the gravity of a star stretches the lightwaves that leave its surface — an effect seen with white dwarf stars. And it predicts that the passage of time is different for observers in different gravitational fields. That’s been confirmed by flying atomic clocks in high-altitude airplanes — and it’s a key factor in the success of a bit of modern technology. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/6/12 | Free | View In iTunes |
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Moving Clouds | Changes in seasons bring changes in cloud cover — not just here on Earth, but on other worlds as well. On Saturn’s moon Titan, for example, a giant cloud system above the north pole vanished as winter gave way to spring. The Cassini spacecraft discovered the cloud deck in late 2006 — near the middle of winter in Titan’s northern hemisphere. The clouds spanned about 1500 miles, so they looked like a beanie cap atop the big, cold moon. Titan is so cold that the clouds were made not of water, but of ethane and methane — organic compounds that are gases in the warmer climate of Earth. It’s likely that some of these compounds were falling from the clouds as rain, filling cold lakes near the north pole. The clouds remained in place throughout the rest of the northern winter — which, like all seasons on Titan, lasts about seven Earth years. But in 2009, as winter ended, the clouds began to vanish. By early spring they were gone, leaving the north pole with clear skies. But more clouds were popping up in the southern hemisphere, indicating that just as on Earth, the clouds on Titan change with the seasons. On Titan, though, the seasonal differences may be more extreme. During summer, Titan’s lakes may evaporate, with the ethane and methane moving to the opposite hemisphere. There, they form fresh clouds that dump heavy rains on the surface, filling the lakes there — part of a constant back-and-forth cycle on this cold, intriguing moon. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/5/12 | Free | View In iTunes |
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Humid Skies | Springtime in much of the United States means muggy days and steamy nights, as moisture moves in from the Gulf of Mexico, creating high levels of humidity. An astronomer at the University of Texas is looking at how the humidity varies on another world: Titan, the largest moon of Saturn. Titan’s atmosphere is similar to Earth’s. It’s thick, it’s made mainly of nitrogen, and it supports a weather cycle that includes clouds and rainfall. But Titan is hundreds of degrees colder than Earth, so the clouds and rainfall are made not of water, but of liquid methane. The Cassini spacecraft has made dozens of close passes by Titan, providing many details about its atmosphere. But it watches Titan for only a few hours or days at a time, with long gaps between passes. Texas astronomer Laurence Trafton is using observations from ground-based telescopes to fill in the gaps. In particular, he’s measuring the amount of methane in the atmosphere at different points on Titan. Since methane fills the same role as water does here on Earth, measuring the amount in the atmosphere reveals the humidity — how “muggy” Titan’s air gets. Monitoring Titan will reveal how methane varies by location and by season. And comparing the methane humidity in the summer and winter hemispheres will provide a better picture of Titan’s climate, and reveal where the methane is coming from — helping scientists predict the weather on this cold, humid world. More about Titan tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/4/12 | Free | View In iTunes |
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More Moon and Companions | Titan, the largest moon of Saturn, is a deep freeze, with surface temperatures close to 300 degrees below zero Fahrenheit. But it would be even colder without one of the components of its atmosphere: methane. The gas traps heat from the Sun, making Titan dozens of degrees warmer. Although it makes up only a small fraction of the dense atmosphere, methane plays a critical role in shaping Titan’s surface because it acts as water does here on Earth: It forms clouds, falls as rain, carves channels, and fills lakes. Planetary scientists aren’t sure where the methane is coming from, though. Methane floats to the top of the atmosphere, where it’s destroyed by sunlight. The total supply in the atmosphere today wouldn’t last more than 10 million years. So more methane must somehow be entering the atmosphere. Scientists have looked at several possibilities. One is that there may be deposits of methane-rich ice far below the surface. Some of the ice occasionally makes its way to the surface, adding fresh methane to the atmosphere. Scientists are combining observations from spacecraft and ground-based telescopes to try to pinpoint the source of this critical ingredient in Titan’s atmosphere; more about that tomorrow. Bright golden Saturn stands high above the Moon as night falls this evening, with the star Spica close to Saturn’s lower right. Through a telescope, Titan looks like a tiny star quite close to the giant planet. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/3/12 | Free | View In iTunes |
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Moon and Companions | [SFX: Huygens entry] That’s the sound of the atmosphere of Titan, the largest moon of Saturn, whizzing past the Huygens probe as it parachuted toward the surface in 2005. The probe and its mothership, Cassini, found that like Earth, Titan’s atmosphere consists of a series of layers. But because Titan’s gravity is weaker than Earth’s, its atmosphere extends much farther into space. Titan is the only moon in the solar system with an appreciable atmosphere. The air is denser than Earth’s, and much colder. It consists mainly of nitrogen — the main ingredient in the air here on Earth — with a small amount of methane and other compounds. The outermost parts of the atmosphere are mere wisps of gas. Below those wisps there’s an orange haze that’s rich in organic compounds — the equivalent of smog. And below that, there are layers of clear air sandwiched around a layer that supports clouds. These clouds appear to rain methane onto Titan’s surface, where it carves channels and fills lakes. One of the puzzles about Titan’s atmosphere is where the methane comes from. It’s a lightweight gas that floats to the top of the atmosphere, where it’s destroyed by sunlight. That means something is pumping more methane into the atmosphere; we’ll have more about that tomorrow. In the meantime, look for Saturn to the lower left of the Moon this evening. It looks like a bright golden star, with the true star Spica nearby, a bit closer to the Moon. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/2/12 | Free | View In iTunes |
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Titan | There are only two worlds in the solar system where rain falls on a solid surface, carving riverbeds and filling broad, dark lakes. One of them is Earth. The other is Titan, the largest moon of Saturn. But there’s one big difference between them: temperature. Titan is more than 300 degrees colder than Earth is, so the liquid that falls from its skies and fills its lakes is not water, but methane. Titan is the second-largest moon in all the solar system — about as big as the planet Mercury. But it ranks second to none in the “intriguing” category. For one thing, it’s the only moon with a thick atmosphere — more than half again as thick as Earth’s. And like Earth, the atmosphere supports a cycle of rainfall and evaporation. It’s not yet clear whether the rainfall takes the form of a steady drizzle or periodic showers. The rains fill lakes near Titan’s poles, but just how that works is also unclear. It could be that the lakes remain at least partially full year-round, and the rains just top them off. Or a more likely scenario is that the lakes dry up during summertime and refill during winter. Perhaps most intriguing of all, Titan contains many of the organic building blocks for life — not just methane, but many of the other compounds from which life arose here on Earth. So Titan may well be a chilly version of a very early Earth — a world with all the ingredients for life. We’ll have more about Titan tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 5/1/12 | Free | View In iTunes |
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Moon and Mars | Two NASA spacecraft are entering their final month of work — mapping the gravitational field of the Moon in exquisite detail. Their efforts will help scientists understand the way the Moon is put together, from its blotchy skin to its heavy core. The probes form a mission known as GRAIL. And they’re not alone in their lunar studies — three other craft are also orbiting the Moon. One is taking the sharpest pictures of the lunar surface ever snapped from orbit. The others are studying the Moon’s composition and its interaction with the solar wind. Having five working spacecraft in lunar orbit is a record. Even during the busy days in the run-up to the Apollo missions, NASA never had more than two fully operational craft at the Moon at one time. GRAIL began its science mission in early March. The two craft follow the same orbital path, with one craft trailing the other. Instruments aboard the craft measure their distance from each other to less than a thousandth of an inch. Such tiny changes in distance reveal variations in the Moon’s pull, yielding detailed maps of its gravitational field. The mission will end around the end of May, though, because the two craft will no longer be able to track each other — turning the quintet of active lunar explorers into a trio. Look for the Moon in the south at nightfall. Another world that’s getting a detailed look stands above it: the planet Mars. It looks like a fairly bright yellow-orange star. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 4/30/12 | Free | View In iTunes |
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Moon, Mars, and Regulus | The stars yield their secrets grudgingly. Consider Regulus, the brightest star of Leo, the lion. It’s directly above the Moon as night falls this evening, with the planet Mars close to its left. For most of human history, Regulus was no more than a bright point of light in the night sky. But it held a special place in human affairs because it lies along the Sun’s path across the sky. In ancient Persia, it was one of four “royal” stars -- the guardians of the night. The first observers to look at Regulus with a telescope found that it’s a double star -- the bright star that we see as Regulus, plus a fainter companion. And in 1867, an astronomer found that the companion is also a double star. About that same time, astronomers also got their first good measure of Regulus’s distance. And in the late 20th century, they got their first good measure of its size. Not until a few years ago, however, did they get a really complete dossier on Regulus. It’s several times the size and mass of the Sun, and about 350 times brighter; it spins so rapidly that it looks like a squashed beachball; and Regulus itself has a small companion in a tight orbit -- a “dead” star known as a white dwarf. Yet there’s a lot about Regulus we don’t know. Its age is a bit muddled, for example. The star itself looks young, yet the presence of the white dwarf suggests it’s much older. Even today, Regulus continues to guard its secrets. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 4/29/12 | Free | View In iTunes |
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Centaurus A | Some galaxies are calm and serene. But others emit copious amounts of radio waves -- a sure sign that they’re anything but calm. The nearest such galaxy is in the southern constellation Centaurus, about 12 million light-years from Earth. Now known as Centaurus A, the galaxy was discovered by a man born in a country located so far north that its inhabitants never see it. But in the early nineteenth century, Scottish astronomer James Dunlop traveled to Australia, where he scanned the southern skies with a small telescope. On the night of April 29th, 1826, in the 10 o’clock hour, Dunlop spotted a nebula that seemed to have two parts. He had no idea that it was a galaxy beyond our own. More than a century later, other astronomers in Australia detected radio waves from the constellation Centaurus. The following year, these astronomers moved to a better site in New Zealand and found that the radio waves came from the galaxy Dunlop had seen in 1826. Today, we know quite a bit about Centaurus A. It’s an elliptical galaxy -- a type that normally lacks gas and dust and the young stars they produce. But Centaurus A has probably swallowed a smaller galaxy, which splashed dust across it. This extra dust creates a dark lane that seems to split the galaxy in two, explaining why its discoverer thought it was really two objects sitting side by side. The collision also caused the radio waves -- making Centaurus A the nearest radio galaxy to Earth. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 4/28/12 | Free | View In iTunes |
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Brilliant Venus | The planet Venus is always a dazzler. It outshines everything else in the night sky except the Moon, and is even bright enough to see during the daytime -- if you know just where to look. Now, though, thanks to a couple of factors, the planet is at its brilliant best. It shines more than 20 times brighter than the brightest true star in the night sky. One of those factors is distance. Venus and Earth are moving closer together, and will be closest in early June, when the planet crosses between Earth and the Sun. In fact, it’ll pass across the Sun, creating a rare astronomical event known as a transit. Another factor is the fraction of the hemisphere that faces Earth that’s illuminated by the Sun. Venus is a thick crescent right now, just like a crescent Moon. Over the coming weeks, that crescent will grow thinner as Venus moves closer to the Sun in our sky. At times, we actually see an almost full Venus, when you might expect the planet to shine brightest. But that phase occurs when Venus is on the opposite side of the Sun from Earth, so the greater distance dulls its luster. So when you combine the planet’s distance and its phase, the next few nights offer Venus at its best. Look for the planet well up in the west as night begins to fall, shining as the brilliant “evening star.” You just can’t miss it. It drops down the western sky during the evening, and sets by around midnight. Tomorrow: discovering a “loud” galaxy. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine. | 4/27/12 | Free | View In iTunes |
| Total: 28 Episodes |
Customer Reviews
YES!!! A radio classic now an iTune podcast
I've listened to this radio show for 16 years on AM radio here in Los Angeles. This is an EXCELLENT introduction -- two minute snippets -- of our universe. If you are a pocket protector type this may not have enough meat for your plate. But for all of us who gaze upwards into the night sky with wonderment, this is a great appetizer. My eight year old son is hooked... Now if they would only publish it the day of or day before [hint, hint, hint], I'd give it five stars!
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I loved this as a kid and discovered the Podcast not long ago while searching to see if it was broadcast in San Diego. A classic that is sure to interest anybody with an interest in the night sky. Daily stories that you can go out at night and relate to. The Podcast is one day behind the Radio Show, but that doesn't decrease the effectiveness of the show one bit.
A Day Late and a Dollar Short
Great audio, great information. I go running at night so I like to be looking at the night sky for what is talked about, BUT if it is a day late I sometimes miss what is talked about or cannot easily find phenomena because it is a day late.....
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