StarDate Podcast

Summertime ended a month ago, but two astronomical markers of the summer season are still hanging in there. One of them will be gone from view pretty soon, though, while the other will linger a while longer. As twilight begins to drain from the evening sky, look toward the southwest for the sinuous trail of stars that outlines Scorpius, the scorpion. It’s so low in the sky that you need a clear horizon to pick it out. Its brightest star, Antares, shines dull orange, a little below the similarly colored planet Mars. And to the upper left of Scorpius, look for the other summer marker, Sagittarius, the archer. Its brightest stars form the shape of a teapot, with the steamy Milky Way rising from the spout. Scorpius will drop from sight within a few days. But Sagittarius will remain in view until around the middle of next month. All the stars and constellations have their own “seasons” — the time of year when they’re best viewed. For Scorpius and Sagittarius, it’s summer and early fall, when they scoot low across the southern sky for those of us in the United States. Because they’re so far south, they remain in view for a much shorter time than constellations like Leo and Virgo, which climb high overhead. Yet Scorpius and Sagittarius will both return to view when the weather grows hot and the nights grow short — once again heralding a changing of the seasons in the stars. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Halley ’s Comet has made a big mess. The comet has been passing close to the Sun for at least two millennia. And on each pass it sheds a little more debris — tiny grains of rock that are released when ice at the comet’s surface vaporizes. We see evidence of that messiness every October as the Orionid meteor shower, as some of those bits of debris slam into the upper atmosphere, producing the glowing streaks of light known as meteors. The shower should be at its best the next couple of nights. And the Moon sets by around midnight, so it won’t pollute the sky with light during the peak meteor-watching hours. Although the Orionids are always one of the year’s best showers, just how good varies. Some years, the shower produces a peak rate of only about a dozen or so meteors per hour. Other years, it’s several times that rate, with an average of around a couple of dozen. And just how long the peak lasts varies, too — from a few hours to a couple of days. That’s because the trail that Halley has left behind is complicated. There are streamers and voids within the trail that are tough to predict. So while just about every year is a good year for the Orionids, some years are better than others. With that in mind, the Orionids are always worth a look. The best viewing hours are after midnight, when your part of Earth turns into the meteor stream. Find a dark but safe skywatching site, then look up — for fireworks from a messy comet. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Back in 2003, astronomers spotted what was then the farthest object ever seen orbiting the Sun — more than eight billion miles away, which is more than twice as remote as distant Pluto is. Since the newfound world lies far from the warmth of the Sun, it must be very cold, so the discoverers named it Sedna, after an Inuit sea goddess who dwelled at the bottom of the Arctic Ocean. At the time of its discovery, Sedna was thought to be roughly two-thirds the diameter of Pluto. But more recent observations have cut Sedna down to size. Because Sedna is so cold, it should emit most of what little heat it does produce at far-infrared wavelengths. Those wavelengths are much longer than the human eye can see, but they’re well within the range of several telescopes in space. One of those, Spitzer Space Telescope, failed to see Sedna at infrared wavelengths. Recently, however, the European Herschel Space Observatory succeeded where Spitzer failed — it picked up distant Sedna’s feeble heat radiation. Its observations indicate that Sedna is just 620 miles across — less than half the diameter of Pluto. The same observations indicate that Sedna reflects about a third of the sunlight that strikes it. Herschel also measured Sedna’s temperature. And as you might imagine, it’s pretty darn low: minus 424 degrees Fahrenheit. So while astronomers initially overestimated Sedna’s size, they did pick a perfect name for this frigid and remote little world. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Moon has a pair of bright orange companions this evening. The two look so much alike that you might think you’re seeing double. The companions are the planet Mars and the star Antares — a name that means “rival of Mars.” They’re close to the lower right of the Moon. Antares is slightly brighter than Mars right now, and it stands a little lower in the sky. While plenty of nightlights twinkle in the sky, not many of them show much color. Most of the stars shine pale white. That’s mainly because they’re so faint — there’s just not enough light to trigger the color receptors in our eyes. So the stars that show any color at all are the ones that look especially bright in our sky. Antares is one of those. It’s hundreds of light-years away, but it’s also one of the biggest stars in the galaxy, so it shines tens of thousands of times brighter than our own star, the Sun. The star’s color comes from its temperature. Its surface is thousands of degrees cooler than the Sun, so it shines reddish-orange. If we could see Antares from close range — as close as the Sun is, for example — we wouldn’t see much color at all. That’s because the star produces some light at all wavelengths. At close range, the light would be so intense that it would saturate the color receptors, so the star would appear white. Only from afar does Antares show its true color — the same color as the planet for which it was named: orange Mars. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The life of a planet is never easy. When it’s young, it’s bombarded by the leftover building blocks from the process that gave it birth. In middle age, the energy from its star varies, changing the planet’s temperature and allowing it to be zapped by cosmic radiation. And at the end, it may be done in by the star’s own demise. Astronomers from England have found evidence of that final stage in the outer layers of white dwarfs — the hot, dense corpses of stars that were once like the Sun. The surface of a white dwarf usually consists of just hydrogen and helium. But using Hubble Space Telescope, the British astronomers detected oxygen, magnesium, iron, and silicon at the surfaces of four white dwarfs — the materials that make up almost all of Earth and the other rocky planets in our own solar system. These elements must have come from outside the star. Yet such heavy materials would quickly sink into the white dwarf’s center, so the supply must be renewed. The astronomers say that means there’s a “rain” of residue from one or more Earth-like planets — up to a thousand tons a second. As a Sun-like star ends its life, it puffs up, then ejects its outer layers into space. This process may knock some of the planets out of their orbits and cause them to ram together. That could pulverize the planets, leaving a ring of debris. The debris then rains onto the surface of the white dwarf — ending a planet’s life in the embrace of its parent star. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Astronomers have found planets orbiting all kinds of stars. Yet they haven’t found planets orbiting the dead stars known as white dwarfs. But one astronomer says they shouldn’t be hard to find — and that some of those planets could even be like Earth. A white dwarf is the dead core of a once-normal star like the Sun. It no longer produces nuclear energy, but it continues to shine because it’s extremely hot. The typical white dwarf is about 60 percent as massive as the Sun, but only about as big as Earth. White dwarfs are so dim that not a single one is visible to the unaided eye. Yet they’re quite common — they account for one of every 20 stars in the Milky Way galaxy. Last year, Eric Agol of the University of Washington wrote that white dwarfs could harbor Earth-like planets at just the right distance from their star for life to exist. Agol reported that if such planets exist, they should be easy to find. Because a white dwarf is so small, an Earth-sized planet that passed in front of it would block nearly all of the star’s light. Detecting such a deep eclipse would require only a small, inexpensive telescope. The idea is highly speculative, though, because it doesn’t explain how a planet would survive the process that created the white dwarf in the first place. Even so, it gives astronomers one more place to look for planets — including worlds that could be similar to our own. More about white-dwarf planets tomorrow. Script by Ken Croswell and Damond Benningfield For more skywatching tips, astronomy news, and much more, read StarDate magazine.

There are lots of ways to split up the night sky. One of the most natural is to divide it into northern and southern halves. And in fact, astronomers have done just that with the celestial equator — the projection of Earth’s equator on the sky. You can trace the equator’s path this evening by following several constellations, which stretch from due west, to high in the south, to due east. As darkness falls, Ophiuchus, the serpent bearer, is well up in the west, flanked by the divided halves of the serpent. None of their stars are all that bright. But Ophiuchus takes up a huge chunk of the sky, so if you look up from the western horizon, you’re looking right at it. Fairly high in the south, there’s a more prominent constellation — Aquila, the eagle. Its brightest star, Altair, is a little above the equator. Altair is one of the points of the bright Summer Triangle, so it’s easy to pick out. And over in the southeast there’s another faint constellation, but one that’s well known: Aquarius. A couple of its brighter stars lie almost atop the celestial equator. And if you stay up until midnight, you’ll see the most famous equatorial denizens of all — the three stars of Orion’s Belt. They form a short line that’s almost due east. The Belt’s top star, Mintaka, is just a fraction of a degree from the equator. Orion climbs across the sky during the night — with his top half in northern skies, and his bottom half in the south. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Every star tells a tale. It tells us how big it is, how hot it is, how it’s moving through space, and even what stage of life it’s in. The story is told in the star’s spectrum — the rainbow of colors that’s produced when you split starlight into its individual wavelengths. But sometimes, the story is difficult to decipher. Consider Deneb Algedi, a star whose name means “tail of the kid” — a reference to its position at the tail of Capricornus, the sea-goat. The constellation is in the south at nightfall. Its brightest stars form an outline that looks like the bottom of a bikini bathing suit, with Deneb Algedi at the left point. We do know that the star is bigger, hotter, and brighter than the Sun, and that it’s about 40 light-years away. But the rest of the story is unclear. Astronomers are sure that the star is around the end of its “normal” lifetime — the long stretch when it burns the hydrogen in its core to produce helium. But they’re not quite sure just where the star is in this process. It could be in the final days of its hydrogen-burning phase. Or it could have completed that phase and moved into the next phase, where it begins burning the helium to make heavier elements, and puffs up to become a giant. Or it could be in the transition stage between those phases — basically marking time until the core triggers the process of helium fusion. The answer is yet to be deciphered — hidden in the star’s light. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Few of us want to be thought of as the tail — the one who’s always bringing up the rear. But in the sky, tail stars are pretty common. More than a half-dozen of them have names that include the Arab word “Deneb,” which means “the tail.” The most famous of these tail stars is Deneb itself — the tail of Cygnus, the swan. It’s directly overhead as night falls right now. It’s the most impressive of all the tail stars because it’s a supergiant — one of the biggest, heaviest, and brightest stars in all the galaxy. And it’s fated to explode as a supernova — singeing the swan’s tail feathers. The next-best known tail star is Denebola, the tail of the lion. It’s quite low in the east at first light, bringing up the rear as the lion springs across the sky. Several other constellations also have tail stars. There’s Deneb Dulfim, the tail of the dolphin, for example, and Deneb Kaitos, the tail of Cetus, the whale or sea monster. And one constellation has two tail stars. Aquila, the eagle, has two bright stars at the eagle’s end. Together, they’re known as Deneb al Okab. Another tail star puts in its best showing during the nights of autumn. Deneb Algedi is the tail of the “kid,” part of the constellation Capricornus, the sea-goat. The constellation is low in the southern sky at nightfall. It looks like a wide triangle, with Deneb Algedi at the left point — bringing up the rear of the sea-goat. More about Deneb Algedi tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A wide swath of the southern sky is known as the Celestial Sea — a series of constellations associated with water. All of them were created and named millennia ago, at a time when their appearance in the night sky heralded a rainy time of year. The leading edge of that wave of watery constellations is Capricornus. It’s fairly low in the southern sky as night falls at this time of year. Its brightest stars form a wide triangle that looks like the bottom of a bikini bathing suit. The constellation itself represents a “sea goat” — a creature with the head and shoulders of a goat and the tail of a fish. One story says it represents the god Pan, who dived into the water to save himself from a nasty monster. He transformed his lower body into a fish in the process. Capricornus doesn’t have any particularly bright stars, so you need dark skies to pick it out. But its borders do contain an interesting deep-sky object — a globular star cluster known as M30. It’s about 30,000 light-years away, and it’s a ball of stars that spans about a hundred light-years. Its stars are among the oldest in the galaxy — billions of years older than the Sun. Such stars are all small and faint. So even though M30 contains more than a hundred thousand stars, you need binoculars to see it. To give it a try, scan to the lower left of the constellation’s pattern of bright stars — the edge of the great Celestial Sea. More about Capricornus tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

On many cell phone calls, there’s a noticeable delay in the conversation — a lag of a fraction of a second that often has people talking over each other. That’s a small taste of what it’s like to communicate with people or spacecraft at other worlds. Radio waves travel at the speed of light, which is 186,000 miles per second. When you consider the great distances between worlds, the seconds add up in a hurry. The round-trip travel time between Earth and Moon is two-and-a-half seconds. That created a lot of double-talk between Apollo astronauts and mission control. Even so, they could hold two-way conversations, and flight controllers could keep an eye on spacecraft systems. But for spacecraft at other planets, the lag time is much greater. Tonight, for example, the planet Venus is more than a hundred million miles away. At that distance, it takes radio waves more than nine minutes to travel from Venus to Earth. So if the orbiting Venus Express spacecraft were to encounter a problem right now, it would take almost 20 minutes for engineers to learn about it and send a response — a gap that could endanger the mission. So when a spacecraft at another world encounters a problem, it shuts down most of its systems and waits for instructions from home — a good while later. Venus stands just to the left of the Moon at first light tomorrow. The planet looks like a brilliant star — whose light traveled more than nine minutes to reach your eyes. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The powdery “dirt” that covers much of the lunar surface is almost as dark as charcoal. In the far-distant past, though, it was almost white. It’s been darkened by exposure to radiation — mainly the flow of charged particles from the Sun known as the solar wind. Yet the lighter color still shows through in some beautiful patterns known as lunar swirls. They look like dollops of cream being swirled into a cup of coffee. A recent study says the swirls are protected by magnetic “bubbles” that deflect the solar wind. The Moon doesn’t generate a magnetic field today, but it did in the distant past. That magnetized the rocks, which create their own magnetic fields around them. The study found that in places, these fields produce magnetic bubbles that extend dozens of miles above the surface. They deflect the negatively charged particles known as electrons around the bubble. The electrons hit the lunar surface at the edges of the bubble, forming a dark outline. Funneling away the electrons creates an electric field that shoots the positively charged protons in the solar wind back into space. The result is a lunar deflector shield — a magnetic bubble that blocks radiation, keeping the surface below nice and bright. Look for the Moon in the east at first light tomorrow. The bright star Regulus, the “heart” of Leo, the lion, is to its left or lower left. And Venus, the “morning star,” is well below them. More about Venus and the Moon tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Just about every scientist who studies black holes is convinced they exist. But so far, the case is entirely circumstantial — no one has ever actually seen one. A team of astronomers hopes to change that in the next few years. The team is linking radio telescopes around the world to produce sharp images of the possible black holes at the centers of galaxies. The project is known as the Event Horizon Telescope. The event horizon is a black hole’s “surface” — the point of no return for anything that falls into the black hole. Matter and energy pass through the horizon, but only in one direction — nothing can come back out, including light. Albert Einstein’s theory of gravity says that a black hole should bend the light from objects behind it to produce a bright ring — an effect that would make it possible to “see” the black hole. The project will target the supermassive black holes at the center of the Milky Way and another galaxy, M87. Although these are huge objects, they’re so far away that they are tiny in our sky — the size of an orange at the distance of the Moon. Combining telescopes at locations around the world provides sharper views — it’s like seeing with a part of a giant telescope. So far, the project has used a few telescopes. Project leaders are trying to upgrade some of those telescopes, while adding others to the network — steps that could provide undeniable proof that black holes really do exist. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The things we see in the night sky aren’t always what they seem. An example is an object that was discovered 125 years ago today. Lewis Swift found it during a night of observing at Warner Observatory in New York. He described it as a faint star surrounded by nebulosity — in other words, a cloud of gas and dust. But a half-century later, another astronomer realized that it’s not a star at all — it’s a small galaxy. Cataloged as IC 10, it turns out that it’s a member of our own galactic neighborhood, the Local Group. IC 10 is unique among the group’s members because it’s been undergoing intense bouts of starbirth. Astronomers see evidence of these waves of starbirth in the large number of massive stars that are ending their lives. These stars are much heavier than the Sun, so they live much shorter lives. Since they’re all in the same stage of life now, they must have been born at about the same time. IC 10 is about two-and-a-half million light-years away, which makes it one of our closer galactic neighbors. But it’s only a few percent as massive as the Milky Way, so it’s small and faint. And it’s hidden behind clouds of dust in the Milky Way, so it’s tough to study — adding to the uncertainty about this small but busy star factory. IC 10 is in the constellation Cassiopeia, which wheels high across the north on October nights. Its brightest stars form a letter M or W, twinkling through the hazy band of the Milky Way. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Our Sun is a single star, traveling through the galaxy all alone. But many star systems are double or even triple. That includes the nearest star system to our own, Alpha Centauri. Its proximity, combined with the fact that two of its three stars are similar to the Sun, makes it one of the brightest stars in the night sky, although it’s too far south to see from most of the United States. In contrast, the next-nearest triple star system is so dim that you need a telescope to see it. Luyten 789-6 resides in the faint constellation Aquarius. It’s 11 light-years from Earth, so it’s almost three times farther than Alpha Centauri. The star system takes its name from Willem Luyten, an astronomer at the University of Minnesota who discovered it in the 1930s. It’s the 12th-closest star system to the Sun. Luyten 789-6 is faint because it consists of three red dwarfs. Such stars generate energy just as the Sun does — through nuclear reactions in their cores that convert hydrogen into helium. But red dwarfs are much less massive than the Sun. That makes their cores much cooler, which in turn cools the pace of their nuclear reactions. That makes these stars the most feeble in the galaxy — they put out only a small fraction as much energy as the Sun does. So even though it’s one of our closest neighbors, the triple-star system of Luyten 789-6 is so faint that no one knew of its existence until less than a century ago. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.