StarDate Podcast

[SFX: RBSP solar sounds] Although it sounds like a strange aviary, this is really the sound of particles from the Sun interacting with Earth’s magnetic field. It was recorded by a pair of spacecraft launched earlier this year. Together, the craft are known as the Radiation Belt Storm Probe. They’re designed to study a region around Earth that most spacecraft try to avoid: the Van Allen radiation belts. The belts are wide zones where Earth’s magnetic field traps electrically charged particles from the Sun. Long exposure to the belts can damage or knock out satellites and endanger the health of astronauts who travel to the Moon or beyond. Crews aboard the International Space Station are safe because they’re generally below the belts. But when Earth is pelted by especially strong storms on the Sun, the belts can change. In particular, the outer belt can become much stronger, and expand farther into space. At times, it can envelop communication satellites in high orbits. The new probes use special electronics and heavy shielding to protect them from the radiation. That’ll allow them to loop through the Van Allen belts for two years or longer. Scientists will use their observations to learn how the belts change during solar storms. That could provide new tools to help forecast the effects of the storms on Earth’s own space environment — offering extra protection against stormy skies. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

It’s pretty easy to define the surface of Earth. Just trip over a rock, or even jump off a pier, and you won’t have any trouble telling where the atmosphere ends and the surface begins. But many other astronomical objects have no solid surface at all. In many cases, in fact, there’s little difference between the surface and the surrounding atmosphere. A prime example is the Sun. Its visible surface is known as the photosphere. But that surface isn’t solid — it’s a bubbling cauldron of hot gas. And it’s surrounded by an “atmosphere” that’s only slightly less dense than the surface itself. The surface is determined by the density of the gas. Below the surface, the gas is so dense that radiation can’t escape into space. Instead, it’s absorbed by the gas itself. Only at the surface does the density drop enough that radiation can leave the Sun and travel through space — most of it in the form of visible light. Detailed images show that the photosphere isn’t smooth. Instead, it’s made of bubbles of gas that are typically twice as big as Texas. And the Sun’s magnetic field creates temporary features on the surface — cool, dark sunspots, and bright, hot regions known as faculae and plages. The field also creates powerful explosions, as well as big eruptions of hot gas that speed through the solar system. These outbursts can create storms in Earth’s magnetic field, and wreak havoc with modern technology. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

When you’re heading out on a road trip, it sometimes feels like the most time-consuming part of the journey is just getting out of town. The same thing happens with sunlight — it takes far longer for energy to escape the Sun itself than it does for that energy to travel from the Sun to Earth. The Sun generates its energy in its core, which is hundreds of thousands of miles below the surface. The nuclei of hydrogen atoms ram together to form helium atoms, releasing energy. As the energy heads toward the surface, though, it rams into atoms in the core or in the surrounding layer, known as the radiative zone. The atoms absorb the energy, then re-radiate it back into their surroundings. The new energy then rams into other atoms, with the process repeating over and over again. Gradually, though, energy works its way to the next layer outward, the convective zone. In this layer, energy isn’t passed from atom to atom. Instead, blobs of gas heated by the radiative zone rise toward the surface like bubbles in a pot of boiling water. By the time they’ve reached the surface, the blobs have cooled to about 10,000 degrees Fahrenheit, so they radiate their energy mainly as visible light. The trip from the Sun’s surface to Earth takes about eight minutes. But getting from the center of the Sun to the surface — the trip out of the Sun’s own neighborhood — takes much longer: up to millions of years. More about the Sun tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

For those of us in the United States and other northern latitudes, the Sun makes itself scarce at this time of year. In fact, the shortest day of the year — the winter solstice — is coming up on Friday. Despite the colder, shorter days, the Sun still warms our planet just as it’s done for the past four-and-a-half billion years. That warmth is the result of nuclear reactions deep in the Sun’s heart, known as the core. The core accounts for about a quarter of the Sun’s diameter, so it’s hundreds of thousands of miles below the surface. The Sun’s powerful gravity squeezes the core so tightly that it heats it to millions of degrees. At those temperatures, the hydrogen that makes up most of the core consists not of atoms, but of individual electrons and protons — the building blocks of atoms. As these particles zip around, some of the protons fuse together through nuclear reactions to form the nucleus of a helium atom. There’s so much material in the core that this process adds up. Every second, in fact, the Sun converts about 700 million tons of hydrogen to helium. But a little less than one percent of the mass of the original hydrogen is converted to energy — about four million tons per second. It’s this process that causes the Sun to shine. Yet the energy produced in its core isn’t what we see from the Sun’s surface. The Sun’s light is the result of a long and twisting path from the core to the surface — and we’ll talk about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

You may not have noticed it, but the Sun is setting a little later right now than it did a few days or weeks ago. Yet the days are continuing to get shorter, and will until after the winter solstice on Friday. The difference is caused by the fact that there are two ways to figure the length of a day. The one we use defines a day as exactly 24 hours. But the other way follows the motion of the Sun from one solar noon to the next — the moment the Sun is highest in the sky. Under this system, the length of a day can vary by about a half-minute from one day to the next. There are a couple of reasons for that variation. One is Earth’s tilt on its axis, which causes the Sun to rise at different angles and at different locations along the horizon on different days. The other is Earth’s lopsided orbit, which causes the Sun to return to the same point in the sky a little earlier or later in the day depending on whether we’re close to the Sun or far away. When you add these factors together, you find that the earliest sunsets for places like Honolulu and Miami came around the end of November. For higher latitudes, like Philadelphia, they came about a week ago. And for cities that are even farther north, like Anchorage, earliest sunset is happening about now. And to balance things out, the date of latest sunrise comes after the solstice, working from north to south — a few more minutes of darkness before the dawn of another day. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The crescent Moon looks down on the planet Mars this evening. They’re quite low in the southwest as darkness falls, and set not long afterwards. Mars looks like a modest orange star directly below the Moon. Although the Moon and Mars are a long way off, we actually have pieces of them here on Earth. The main source of Moon samples is the Apollo missions of the 1960s and ‘70s; astronauts brought back more than 840 pounds of lunar rock and soil. In fact, the last of those samples, collected by the crew of Apollo 17, began the journey to Earth 40 years ago tomorrow. But pieces of both the Moon and Mars actually made it to Earth on their own, as meteorites — rocks that traveled through space and fell to Earth. These rocks were blasted into space when asteroids slammed into the surfaces of Mars or the Moon. The impacts threw debris clear of their parent worlds. Some of these pieces eventually found their way to Earth. Most of the meteorites from Mars and the Moon have been found in Antarctica or in the deserts of Africa and the Middle East, where there are few Earth rocks to clutter things up. Scientists determine where these rocks come from by carefully measuring traces of gas trapped in tiny bubbles in the rock. They compare these gases to measurements of the Apollo Moon rocks, or to measurements made on Mars by robotic landers. The mixtures of these gases are unique to Mars and the Moon — confirming their extraterrestrial origin. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The planet Venus continues to dazzle in the morning sky this month. The “morning star” is low in the southeast at first light. And right now, the fainter planet Mercury is off to its lower left. Venus is hidden beneath an unbroken blanket of clouds. For many decades, scientists and the public alike expected to find a warm, wet world beneath those clouds — a world of steamy jungles, perhaps filled with prehistoric beasts. By the early 1960s, that concept was starting to crack a little. But it remained intact until 50 years ago today, when Venus was visited by the first successful mission to another planet. Mariner 2 flew less than 22,000 miles from Venus. The craft weighed only a few hundred pounds, and transmitted data a few bytes at a time. Yet Mariner completely transformed our concept of the bright planet. By measuring microwaves produced by Venus, it measured the planet’s surface temperature at about 800 degrees Fahrenheit. In an instant, that wiped away the idea that Venus was a comfortable abode for life. And combined with observations by radio antennas on the ground, Mariner helped pin down the length of Venus’s day — something that couldn’t be done earlier because no one could see features on the surface. It revealed a length of several Earth months. So in a few minutes of observations, Mariner destroyed the concept of Venus as a second Earth — but unveiled a world unlike any other for scientists to ponder. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

NEUGEBAUER: It was just a hair-raising mission. Several things failed and then just recovered by themselves. It took about three miracles to get Mariner 2 to Venus. It just looked like the end several times along the way. Fifty years ago, Marcia Neugebauer oversaw one of the experiments for the first successful mission to another planet. Mariner 2 flew less than 22,000 miles from Venus on December 14th, 1962. In those early days of rocketry, missions failed as often as they succeeded. In fact, a twin Venus spacecraft, Mariner 1, had to be blown up less than five minutes after launch. And the United States still hadn’t even reached the Moon. Mariner 2 was problem-plagued almost from the moment of launch. A sensor had a hard time tracking Earth, one of its solar panels failed, and it overheated. Yet even before it reached Venus, Mariner 2 was making important discoveries. It resolved a dispute, for example, about the solar wind. Most physicists expected to find some sort of flow of charged particles from the surface of the Sun. But there was a major disagreement about the form of that flow. One leading scientist expected a million-mile-an-hour gale. But another expected more of a gentle breeze. Within weeks, Mariner 2 resolved the issue — it discovered a high-speed solar wind that never let up during the long cruise to Venus. But Mariner 2 is best known for transforming our concepts of Venus itself. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The next couple of nights offer some of the best skywatching of the year. For one thing, the brilliant planet Jupiter soars high across the south during the night. It far outshines the other pinpoints of light in the sky for most of the night, so you can’t miss it. And the only pinpoint that outshines it — the planet Venus, the “morning star” — rises before dawn, flanked by two other planets; we’ll have more about Venus tomorrow. And to spice things up a bit more, one of the year’s best meteor showers is at its peak, with no Moon in the way to spoil the show. The Geminid shower actually peaks during the daylight hours tomorrow as seen from the United States. That means that tonight and tomorrow night are both pretty good nights for viewing the shower. The shower is named for the constellation Gemini. That’s because if you trace the paths of its meteors across the sky, they all appear to originate in Gemini. So the best view of the shower comes after Gemini climbs high into the sky in late evening. The meteors can actually streak across any part of the sky, though, so you don’t have to look toward Gemini to see them. The shower’s peak might produce a hundred or more meteors per hour. Since the peak comes during daylight here in the U.S., the nighttime rates will be lower. But there should still be enough meteors to make the shower worth looking for — streaks of light accenting a great night of skywatching. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

It’s been 40 years since Apollo 17 astronaut Gene Cernan took humanity’s final steps on the Moon, leaving the world with this hope for the future: CERNAN: As we leave the Moon and Taurus-Littrow, we leave as we came — and God willing, as we shall return: with peace and hope for all mankind. So far, of course, no one has returned to the Moon at all. And no one is likely to for many years to come. Plans for the next round of human exploration come and go just about as breezily as the seasons. But after a lengthy hiatus, lunar exploration has returned, with the next round of robotic missions. Over the last few years, orbiting American spacecraft have mapped the Moon in unprecedented detail. They’ve also mapped the composition of its surface, and found evidence of ice at the south pole. And a current mission is measuring the Moon’s gravity field, providing a better look than ever at the Moon’s interior. Other nations are exploring the Moon, too. An Indian probe, for example, found evidence that water is mixed with the dirt across much of the lunar surface. The exploration also continues here on Earth, as scientists study the hundreds of pounds of rock and soil remaining from the Apollo missions. Using techniques that didn’t even exist 40 years ago, they’re finding new details about the Moon’s composition, structure, and birth. They’re also helping identify sites for future study — whenever we’re ready to send the next astronauts back to the Moon. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

APOLLO 17: Stand by for touchdown. Stand by. This is an auspicious week in the history of space exploration. 50 years ago, an American spacecraft staged the first successful encounter with another planet — a brief passage by Venus. And just 10 years later, the final crew of the Apollo program landed on the Moon. APOLLO 17: Okay, Houston, the Challenger has landed! We is here! Man is we here! Astronauts Gene Cernan and Jack Schmitt landed on December 11th, 1972, in a valley in the lunar highlands. The site gave them a chance to sample two different types of terrain — the surrounding mountains of the highlands, and a small plain of relatively young volcanic rock on the valley floor. Schmitt was the first and only geologist to visit the Moon. During three moonwalks, he and Cernan picked up more than 240 pounds of rocks and soil. One of the highlights was a patch of bright orange soil, which scientists are still studying today. A recent analysis found that it contains a lot of water, showing that the Moon is much wetter than anyone had expected just a few years ago. And from lunar orbit, the third Apollo 17 astronaut, Ron Evans, operated cameras and other instruments that mapped a large swath of the surface. Cernan and Schmitt rejoined Evans after three days on the Moon, and the crew returned to Earth on December 19th. At the time, most expected astronauts to return to the Moon within a few years, but it hasn’t worked out that way. More about the long break tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The solar system offers a beautiful display at first light tomorrow, as three planets flank the crescent Moon. Golden Saturn stands close to the upper left of the Moon. Dazzling Venus, the “morning star,” is farther to the lower left of the Moon, with shy little Mercury to the lower left of Venus. At least one spacecraft is orbiting each of these worlds right now. And several missions to the Moon are scheduled for the next few years. But the grand era of lunar exploration came to an end 40 years ago this month, with the flight of the final Apollo mission — Apollo 17. Over the preceding dozen years, the United States had launched about 30 missions to the Moon. Many of them failed — especially the early ones. But about 20 succeeded. They dispelled many myths about the Moon, and helped us understand our satellite world in detail — its composition, its structure, and even its origin. They also brought a greater appreciation of our own Earth, showing the vibrant blue world against the blackness of space and the stark grandeur of the Moon. In the 40 years since Apollo 17, the U.S. has sent only about a half dozen missions back to the Moon. And plans for future exploration keep getting axed. So today, the Moon is much as it was a half-century ago — a world beyond our grasp. Even so, it’s a world made familiar by the accomplishments of a bold era of exploration — an era that ended four decades ago. More tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

What we see in the night sky isn’t just a matter of what we perceive with our eyes. It’s also a matter of what we think about it. A lineup of planets in the morning sky this month is a case in point. To most of us, it’s a beautiful celestial display — a picture to savor. But for a few, it’s something to fear. The planets line up to the lower left of the Moon at first light tomorrow. From top to bottom, they’re Saturn, Venus, and Mercury. Venus is by far the brightest of the three — it’s the brilliant “morning star.” And to add to the display, the star Spica is quite close to the upper left of the Moon. Whenever there’s a planetary lineup, there’s someone around to proclaim it a harbinger of doom. They warn that the gravitational pull of the planets will cause storms or earthquakes, or something even worse, like flipping Earth over like a spinning soccer ball. The cries of doom are even louder this year because of the idea that the Mayan calendar ends on December 21st, bringing the world to an end with it. There’s not a bit of truth to any of it. The Mayan calendar won’t end, just reset. There’s no prophecy of doom. And planetary alignments are as common as predictions of doomsday. They have no effect on Earth at all. Their gravitational pull on our planet is just too tiny to matter. So if you’re up and about before dawn the next few days, enjoy the lineup of the Moon and planets in the pre-dawn sky. It’s a sight to savor. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

As seen from most of the United States, Capella is the fourth-brightest star in the night sky. And it’s close by, too, at a distance of just 43 light-years. Yet until recently, we couldn’t see that Capella is actually a pair of stars. They’re so close together that even the biggest telescopes couldn’t show us the individual stars. Even so, by using astronomy’s full repertoire of techniques, those same telescopes did reveal a lot about the stars. For example, astrometry, which measures the positions of astronomical objects, revealed that Capella is moving at more than 60,000 miles per hour relative to our motion around the center of the galaxy. Spectroscopy, which breaks light into its individual wavelengths, showed that the system is two stars. It also told us how quickly the stars orbit each other, what they’re made of, and how hot they are. And photometry, which measures changes in brightness, revealed that even though the stars are close together, they don’t really “bulge” out toward each other. Astronomers combined techniques to learn the masses of the two stars, and that both stars are nearing the ends of their lives. In recent years, new techniques have produced sharp images of Capella, finally showing us what astronomers have known for a long time: that Capella is two stars that shine as one in our night sky. Capella is in the northeast at nightfall. It arcs high overhead later on, and is in the northwest at first light. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A pair of bright stars with an even brighter future highlights the northern sky on December nights. Capella, the brightest star of Auriga, the charioteer, is in the northeast as night falls, far to the left of the dazzling planet Jupiter. The yellow star arcs high overhead after midnight, and is in the northwest at first light. What looks like a single point of light is really two stars that are gravitationally bound to each other. They’re closer together than Earth is to the Sun, so even with giant telescopes it’s almost impossible to see them as individual stars. Each star is about two-and-a-half times as massive as the Sun, and a good bit bigger and brighter. And in the years ahead, they’ll get bigger and brighter still. That’s because both stars are nearing the ends of their lives, so they’re undergoing changes that are causing their outer layers to puff up. Over time, each star should puff up to dozens of times the Sun’s diameter, and shine hundreds of times brighter. Then the stars will blow off their outer layers, leaving behind their exposed cores, known as white dwarfs. But how that’ll play out is uncertain. As the first one puffs up, it’ll transfer some of its gas to the other, altering the evolution of both stars. The clouds of gas around them will drag the two stars closer together. In the far distant future, they could slam together, creating a supernova — blasting both stars to cosmic dust. More about Capella tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.