StarDate Podcast

When the Voyager 1 spacecraft arrived at Saturn in 1980, scientists were almost as eager to see Saturn’s largest moon as they were the planet itself. Observations from the ground had detected an atmosphere. But Titan is so small and far away that no one could learn much about it, or see how it affected the surface below. It turned out that Voyager couldn’t see the surface, either, because the atmosphere is topped by a thick haze. So all the craft saw was a featureless orange ball. But its instruments did reveal that Titan’s atmosphere is thicker than Earth’s, and that it consists mainly of nitrogen — the main ingredient in Earth’s atmosphere as well. Voyager also detected a mixture of hydrocarbons in the air, such as methane and ethane. And it measured a surface temperature of about 300 below zero Fahrenheit. Planetary scientists soon speculated that methane and ethane could fill an ocean that would cover Titan’s entire surface. But 15 years after Voyager, Hubble Space Telescope peered through the haze to provide a rough look at the surface, and it found no evidence of an ocean. But we didn’t get a really good look at Titan until Cassini entered orbit around Saturn in 2004. It used radar and other instruments to see the surface. Its observations have revealed lakes of liquid methane and ethane, riverbeds, and giant sand dunes. These features keep Titan’s surface young — and we’ll talk more about that tomorrow. Script by Damond Benningfield, Copyright 2012 This program was made possible in part by a grant from the NASA Science Mission Directorate. For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The planet Saturn is quickly pulling into view in the morning sky. It’s low in the east-southeast at first light, and looks like a fairly bright star. Right now, it’s to the lower left of Venus, the “morning star.” The two will slide past each other in a few days. A telescope will show you Saturn’s largest moon, Titan. In fact, if you look at Titan with even a modest backyard telescope, you’ll know almost as much about the little world as professional astronomers did until well into the last century. It held onto its secrets because it’s so far away. Dutch astronomer Christaan Huygens discovered Titan in 1655. In the 1880s, George Hill determined its mass by measuring its gravitational effects on the orbit of another of Saturn’s moons. The first big breakthrough in understanding Titan came in 1944. Using the brand-new 82-inch telescope at McDonald Observatory, Gerard Kuiper detected the chemical “fingerprint” of methane, demonstrating that Titan has an atmosphere. It was the first moon in the solar system known to have any atmosphere, and it’s the only moon with a thick atmosphere. Bigger telescopes allowed astronomers to see Titan more clearly, yet they revealed few details. That’s because a thick “haze” at the top of the atmosphere conceals not only the surface, but the rest of the atmosphere. More details about Titan awaited its first visitor from Earth — the Voyager 1 spacecraft. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 This program was made possible in part by a grant from the NASA Science Mission Directorate. For more skywatching tips, astronomy news, and much more, read StarDate magazine.

As befits its name, Cetus, the whale or sea monster, is one of the largest constellations in the sky. It glides across the southern sky on November evenings. Despite its size, though, Cetus isn’t prominent, because like most autumn constellations, it lacks brilliant stars. Still, Cetus does boast one of the brightest red-giant stars in the heavens. The star is known as Menkar or Alpha Ceti, and it shines in the whale’s head. A good star map can help you find the star and the rest of the constellation. Menkar is about 250 light-years from Earth, so the light you see from the star tonight actually left its surface shortly before the signing of the Declaration of Independence.Menkar was once a main-sequence star, so it generated energy as the Sun does — by converting hydrogen into helium in its core. But the star burned up the hydrogen in its core, so it had to burn hydrogen in a thin layer around the core. This caused the star to expand. Since an expanding gas cools, Menkar’s surface temperature dropped. So the star turned yellow, then orange, and then finally red. Today, the star is a red giant — a star that’s so large that if it were to take the Sun’s place in our own solar system, it would engulf the planet Mercury. And in fact, Menkar gives us a preview of the Sun’s distant future. In several billion years, the Sun’s core will run out of hydrogen, and our star will slowly expand until it becomes a red giant — just like Menkar. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

There's much more to most stars than meets the eye. A good example is Spica, the brightest star of the constellation Virgo. It's in the east at dawn tomorrow, just to the right of Venus, the brilliant "morning star." Spica is pretty impressive to the eye alone — it's one of the brightest stars in the night sky. But what our eyes can't see is that Spica is actually two stars. Both stars are a good bit bigger and heavier than the Sun, but they're only a few million miles apart, so they're impossible to see as individual stars even through a large telescope. There's something else our eyes miss, although they do give us a hint. Spica shines blue-white, indicating that its stars are quite hot — thousands of degrees hotter than the surface of the Sun. Such hot stars produce most of their light not at visible wavelengths, but in the ultraviolet. When you combine the visible light from Spica's two stars, they shine about 2,000 times brighter than the Sun. But when you throw in the ultraviolet, they're about 14,000 times brighter than the Sun. Even if our eyes were sensitive to ultraviolet as well as visible light, though, Spica wouldn't look any brighter than it does now. That's because Earth's atmosphere absorbs almost all ultraviolet light before it can reach the surface. So the only way to study the ultraviolet is to loft telescopes on balloons or spacecraft — adding extra "eyes" to help us see the wonders of the universe. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A couple of nice conjunctions bracket the sky tonight, one in early evening, the other at dawn. And a third skywatching treat will fill the hours between them — a meteor shower. The action begins as evening twilight drains from the sky, with the Moon and the planet Mars in the southwest. Mars looks like a modestly bright orange star. It’s to the lower right of the Moon, by about the width of your fist held at arm’s length. Fortunately, the Moon is in its crescent phase right now, so it sets about three hours after the Sun. That leaves plenty of dark hours for watching the Leonid meteor shower, which should be at its best tonight. Earth is flying through the orbital path of a comet, sweeping up grains of “comet dust.” As these tiny particles hit the upper atmosphere, they vaporize, forming the streaks of light known as meteors. The dust is pretty thin at this point in the comet’s orbit, though, so we probably won’t see more than a dozen or so meteors per hour. The best view comes in the wee hours of the morning, as your part of Earth turns most directly into the meteor stream. By the time the sky begins to lighten, the third part of the triple feature will be in view in the east — a close pairing of the planet Venus and the star Spica. Venus is the “morning star,” so you can’t miss it. Spica will stand close to the lower right of Venus. And the two of them will line up side by side on Sunday morning; more about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The planet Mars has more or less parked itself in the evening sky right now. It’s quite low in the southwest as night falls, and sets a couple of hours after sunset. Tonight, it’s not far to the upper left of the crescent Moon, so it’s a little easier to pick out than on most evenings. It looks like a modestly bright orange star. Mars is about two-thirds of the way around the Sun as seen from Earth — a little less than 200 million miles away. Over the next few months, it’ll inch farther from Earth, eventually passing behind the Sun next April. Thanks to the relative motions of the two planets, and the time of year here on Earth, Mars won’t appear to move too much in the evening sky, though. It’ll creep to the right along the horizon, eventually appearing almost due west instead of southwest. But from night to night, its altitude above the horizon will remain almost the same at the same hour. And its brightness won’t change much, either. The background behind Mars will change substantially, though, as the planet continues its usual eastward motion against the background of stars. Tonight, it’s near the “spout” of teapot-shaped Sagittarius. By the first of the year, it’ll be one constellation over, in Capricornus. And by the time it disappears in the Sun’s glare around the end of February, it’ll be at the eastern edge of Aquarius. So keep an eye on Mars as it lurks in the fading glow of twilight over the next few months. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Some discoveries are just sweeter than others — sometimes literally. Earlier this year, for example, astronomers discovered a type of sugar molecule close to a distant star. The discovery is especially sweet because sugars form some of the basic chemical building blocks of life. The sugar was found at a young, Sun-like star that’s part of a binary system. The system is about 400 light-years away, in the constellation Ophiuchus. The sugar is known as glycolaldehyde. It’s already been seen in giant interstellar clouds near the heart of the Milky Way galaxy. But those clouds are quite cold. The molecules seen in the star system are in a much warmer region — about as far from the star as Uranus — the seventh planet out — is from the Sun. That’s a region where planets could be taking shape. Glycolaldehyde is a fairly simple molecule. But it can combine with another type of sugar to form one of the chemical building blocks of RNA, one of the basic molecules of life. So if the glycolaldehyde found its way onto the surface of a planet with liquid water, it would complete the list of ingredients needed to form life like that found on Earth. Of course, it’s a long way from the building blocks of life to life itself. But finding them in the right location increases the odds that we may someday find evidence of life on other worlds — a discovery that could well be the sweetest of all. Tomorrow: a planet hovers in the west. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Mars is passing in front of the center of the Milky Way galaxy this week. The planet looks like a modest orange star in the southwest in early evening, above the “spout” of teapot-shaped Sagittarius. The galaxy’s center is about 27,000 light-years beyond Mars, and it’s hidden behind billowing clouds of interstellar dust. One of those clouds is just a few hundred light-years from the center itself. Known as Sagittarius B2, it’s one of the busiest stellar nurseries yet discovered — it’s giving birth to thousands of new stars. It’s also a busy molecule factory. In fact, just about every molecule that’s been detected anywhere in space has been seen in Sagittarius B2. The most complicated molecules may form on the surfaces of the cloud’s dust grains. Simple molecules may stick to these grains, which may be coated with thin layers of ice. Over time, the molecules migrate across the dust grains, allowing them to link up. When the dust grains pass close to a newborn star, their ice vaporizes, releasing the new molecules into space. The list of molecules includes some of the precursors of life, such as some types of sugars. One of the most complicated yet seen is glycolaldehyde. It can link with another sugar to form a key molecule in RNA and DNA, which contain the genetic code of life. Glycolaldehyde was recently seen around a young star — a discovery with implications for life on other worlds. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

If you happen to find yourself along Australia’s Great Barrier Reef around sunrise tomorrow, Nature will offer up one more spectacle in addition to the clear waters and colorful fish: a total solar eclipse. It’ll last a couple of minutes before the Moon’s shadow heads across the vast open waters of the South Pacific. A total solar eclipse takes place when the new Moon passes directly between Earth and Sun, covering the solar disk and briefly turning day to night. That allows the Sun’s faint outer atmosphere, the corona, to shine with a pearly glow around the Moon. But the Moon’s orbital path is tilted a bit with respect to the Sun, so most months the Moon passes a little above or below the Sun, so there’s no eclipse at all. This eclipse is an especially good one because it happens around the time the Moon is closest to Earth. That makes the Moon look a bit bigger, so the eclipse lasts a little longer — a maximum of about four minutes. But the path of the eclipse isn’t very good for skywatchers. About the only inhabited land it crosses is northern Australia. Most of the rest of Australia, all of New Zealand, and parts of Antarctica will see a partial eclipse. Those of us in the United States are out of luck — we won’t see any eclipse at all. Several web sites will broadcast all or part of the eclipse live, though. The total phase of the eclipse begins around 2:35 p.m. Central Time and ends a bit more than three hours later. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The coldest temperatures ever seen here on Earth were recorded at a research station in Antarctica, not far from the south pole. On the planet Saturn, though, the south pole is the site of the warmest temperatures yet recorded — about a hundred degrees warmer than at the equator. That hotspot is inside the south polar vortex — a hurricane-like storm that’s as wide as Earth. It has a large central “eye,” just as hurricanes do, that’s surrounded by two walls of clouds. Clouds in the outer wall are about 20 miles high, while those in the inner wall are twice as high. And winds at the edge of the vortex reach speeds of about 350 miles per hour — twice as strong as the most powerful hurricanes on Earth. Like hurricanes, the vortex must be powered by heat from below it. On Earth, that heat comes from the oceans. But Saturn has no oceans, so scientists are trying to pinpoint the source of the vortex’s heat. And they’re also trying to understand why the heat breaks through only at the south pole — creating a hotspot in Saturn’s cold atmosphere. Look for Saturn quite low in the east about 45 minutes before sunrise tomorrow. It looks like a moderately bright star. It’s a bit tough to see through the glow of early dawn, but the crescent Moon is close to the right of Saturn, helping you pick out the giant planet. Brilliant Venus, the “morning star,” stands well above them, completing a beautiful tableau in the dawn sky. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

As the Moon orbits Earth, the same hemisphere always aims our way. But it’s like the face of a bobblehead doll — it bounces around a little bit. Over the course of the Moon’s month-long cycle of phases, this “bounciness” allows us to see a total of 59 percent of the lunar surface. And until spacecraft began flying around the Moon, that provided the only way to see any of the Moon’s hidden farside. Several factors contribute to these motions, known as librations. The main ones are the Moon’s tilt on its axis and its changing orbital speed. The Moon’s axis is tilted a bit with respect to its orbit around Earth. That causes first its north pole and then its south pole to tip toward us. That allows us to see over the poles a bit, revealing a smidgen of the Moon’s farside. And the Moon’s distance from Earth changes, which causes the Moon to speed up and slow down as it goes around our planet. But the Moon spins on its axis at a near-constant speed. The difference in those two motions allows us to see around the Moon’s eastern and western limbs, adding tiny slivers of lunar territory to the view from Earth. And the view will be especially pretty tomorrow, as the crescent Moon is in the eastern sky at first light. And it has a couple of bright companions. Venus, the “morning star,” is close to the upper left of the Moon. And Spica, the brightest star of Virgo, is a little farther to the lower left of the Moon. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

FORTIN: We have each telescope send a signal when each telescope thinks that there's a nice gamma-ray. Then we combine the signal from all four telescopes... Pascal Fortin is an astronomer with VERITAS -- an odd-looking array of four telescopes in southern Arizona that's designed to probe some of the most energetic objects in the universe. VERITAS is looking for flashes of light produced when gamma rays strike molecules high in Earth's atmosphere. Each collision generates a cascade of other collisions, and each of those can produce a flash of blue light that lasts for a few billionths of a second. High-speed cameras on the telescopes record the flashes. Gamma rays come from quasars, pulsars, gamma-ray bursts, and the remnants of exploded stars, among other exotic objects. So studying them can reveal the conditions in the most extreme environments in the universe. The brightest gamma-ray object is the Crab Nebula -- the remains of a star that was seen to explode almost a millennium ago. It consists of a neutron star, which pumps out a wind of charged particles, and a surrounding cloud of debris from the explosion. When the wind hits the debris, it produces gamma rays. Gamma rays are invisible to the human eye, but the Crab also produces visible light. Through a telescope, it looks like a fuzzy blob with glowing tendrils. It's well to the lower left of brilliant Jupiter and the "eye" of Taurus, which are in the east during the evening hours. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Five telescopes rise from the Khomas Highland of Namibia like giant alien bugs. Their red steel structures look like exoskeletons, their multi-faceted mirrors like compound eyes, and their camera masts like sharp snouts. Also like some other-worldly creature, they see wavelengths of light that are invisible to the eyes of any living thing on Earth — wavelengths produced by some of the most powerful objects in the universe. The telescopes form an array known as HESS — the High Energy Stereoscopic System. Four of the telescopes have main mirrors that span about 40 feet. The fifth, which was dedicated this fall, spans 90 feet. HESS looks for Cherenkov radiation — flashes of blue light that occur when gamma rays strike particles high in Earth’s atmosphere. Seeing the flashes with more than one of the telescopes allows astronomers to track the gamma rays to their source. HESS is the largest Cherenkov detector in the world. The gamma rays are byproducts of exploding stars, the black holes at the hearts of galaxies, and other powerful objects. Magnetic fields and shock waves in these environments accelerate particles to close to the speed of light. Interactions with the magnetic fields or with other particles cause them to emit gamma rays. Studying the Cherenkov radiation can help astronomers understand what’s going on around these exotic objects — an understanding made possible by some exotic telescopes. More tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Namibia is one of the poorest countries in the world. But among the country’s natural resources are great beauty and dark night skies. The beauty is bringing in tourists, while the night skies are bringing casual skywatchers and professional astronomers alike. Not surprisingly, the natural beauty and dark skies often overlap. As an example, a wildlife reserve in the Namib Desert recently became the first site in Africa to earn “dark skies” certification from the International Dark-Sky Association. That means there’s almost no light pollution to obscure the Milky Way, meteors, and other faint sights in the night sky. It also means that the region is taking steps to keep the sky nice and dark. The skies above the Khomas Highland region are nice and dark, too — so nice that they’re home to a growing astronomical observatory. Its major tenant is called HESS. It’s the largest telescope of its kind, which studies some of the most energetic objects and events in the universe; more about that tomorrow. Several smaller projects have added their own telescopes to the site. One of them, called ROTSE, looks for powerful explosions known as gamma-ray bursts. And another, part of a network known as HAT-South, hunts for planets in other star systems. And in fact, astronomers confirmed the first discovery with HAT-South just a few months ago — a giant planet close to a Sun-like star — discovered in part under the dark skies of Namibia. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Milky Way soars high across the sky as twilight fades this evening. It stretches from the brilliant yellow-orange star Capella in the northeast, to the graceful outline of Cygnus, the swan, high overhead, to teapot-shaped Sagittarius in the southwest. If you’re like most Americans, though, you won’t be able to see it — it’s hidden behind a curtain of light: the glare of streetlamps and other artificial light sources. One place you can see the Milky Way, though, is Big Bend National Park in West Texas. It has the darkest measured night skies in the Lower 48 states. So earlier this year, Big Bend was designated as an International Dark Sky Park — an honor bestowed by the International Dark-Sky Association. In part, the park’s skies are so dark because Big Bend is a long away from anywhere. But it’s also because the park, as well as towns and developments around it, have made an effort to control outdoor lighting. The park itself has replaced most of its outdoor light fixtures, cutting the glare considerably — and cutting its lighting costs by 98 percent. Big Bend isn’t alone, though. Natural Bridges National Monument in Utah earned the first dark sky designation, and state parks in Pennsylvania and New Mexico also earned top honors. They’re places where you can always see the Milky Way — and the other glories of the night sky. Africa recently got its first dark-sky park, in a country where astronomy is taking off. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.