StarDate Podcast

It may be the first enduring astronomical myth of the Internet age. Every August, emails, blogs, tweets, and other electronic communications report that Mars will suddenly look as big as the full Moon. If you see that message, please ignore it — it just isn’t so. Mars is low in the southwest at sunset this month, and looks like a modestly bright orange star. It’s a pretty sight, but nothing out of the ordinary. The rumor started in 2003, when Mars passed closest to Earth in about 60,000 years. The planet was brighter than during most close approaches, but only by a bit. At the time, an astronomy publication noted that, through a small telescope, Mars would look as large as the full Moon does to the unaided eye. Yet to the eye alone, Mars itself would remain a star-like point of light. Unfortunately, the story got garbled, then it got spread, then it got to be a pain in the neck. Now, it’s become an electronic myth — one that pops up every August. What’s also about to pop up is the next Mars rover. It’s scheduled to land on Mars on Sunday night, inside a wide crater that may have been filled with water in the distant past. Rock layers at the base of a mountain in the crater’s middle may record that watery era. The nuclear-powered rover will spend two years or longer studying those layers and other formations in the crater — telling us whether conditions on Mars were once comfortable for life. We’ll have more about the rover tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

When we look at a star, all we see is the layer of gas at its surface. But astronomers would like to see a star’s core, because that’s where the action is. Nuclear reactions in the core convert lightweight elements to heavier ones, yielding energy — the energy that powers the star. One way they can learn about the core is to look for ripples on a star’s surface. In fact, by using this technique, the Kepler spacecraft has shown that the cores of some giant stars are spinning much faster than their surfaces. Kepler’s mission is to find Earth-like planets orbiting Sun-like stars. It stares at more than 150,000 stars in the constellations Cygnus and Lyra, monitoring their light for tiny dips that result when a planet passes in front of its star. But the stars themselves also flicker. They vibrate, like a ringing bell, and Kepler is so sensitive to starlight that it can detect these vibrations. Mission scientists have converted some of those vibrations to sound. [SFX: Kepler audio] The vibrations probe a star’s interior just as earthquakes probe Earth’s interior. Kepler observations of three giant stars indicate that their cores spin at least 10 times faster than their surfaces. Billions of years from now, the Sun will swell to the same giant proportions as the stars that Kepler studied. And like those stars, the Sun’s core may spin much faster than its surface — producing flickers of light that will ripple through the galaxy. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Six million years ago, a brilliant star suddenly vanished from view. The star could no longer produce energy in its core to counteract the inward pull of gravity, so in a matter of hours, it collapsed. Its great mass was crushed to an infinitely small point, then hidden from the outside universe — behind the event horizon of a black hole. Although it produces no energy at all, this black hole is one of the most intensely studied objects in the galaxy. It’s known as Cygnus X-1 — the first source of X-rays discovered in the constellation Cygnus. The X-rays come not from the black hole, but from gas that’s stripped from a brilliant companion star. As the gas spirals toward the black hole, it’s heated to hundreds of millions of degrees, so it produces copious amounts of X-rays. Astronomers have been studying the system for 40 years. But it wasn’t until just last year that they finally nailed down the details. They measured the distance to Cygnus X-1 at 6,000 light-years. That allowed them to accurately measure the mass of the black hole — 15 times as massive as the Sun. And they also measured how fast the black hole is spinning — about 800 times per second. Those numbers helped astronomers calculate when the black hole was born, which indicated how it was born. The original star probably didn’t explode as a supernova, which is the birth process for many black holes. Instead, it simply collapsed — giving birth to a black hole. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

For most birds, it’s the beautiful feathers that get most of the attention. And that’s pretty much the case for Cygnus, the celestial swan. To the eye alone, its most impressive sight is Deneb, the bright star that represents its tail feathers. If you look more closely, though, the swan’s fainter beak is far more colorful. Through a telescope, that single pinpoint of light becomes double — one of them golden orange, the other a dazzling blue-white. That contrast makes Albireo one of the favorite double-star targets in the sky. The golden star is actually two stars on its own. They’re so close together that they blur into a single point of light even through a telescope. One of them is orange, while the other is white. The other visible member of Albireo is thousands of degrees hotter than the Sun, hence the blue-white color. It’s not clear if the two visible components are a true binary or just happen to line up in the same direction in the sky. Astronomers determine if two stars are a binary by measuring their relative motions across the sky. If they are bound to each other, then their paths curve around each other. But the components of Albireo are so far apart that there hasn’t been enough time to see that. Albireo is on good display on summer nights. Cygnus is high in the east at nightfall, with its body parallel to the horizon. Brilliant Deneb is at the left end of the body, with Albireo at the right. More about Cygnus tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

When the weather turns colder, many birds head south. But the swan heads west. Cygnus, the celestial swan, is high in the east as night falls during the warm nights of mid-summer. Its body stretches roughly parallel to the horizon, with its tail at the left and its head at the right. Its graceful wings attach about a quarter of the way from the tail to the head, and extend far above and below the body. The tail is marked by the star Deneb, which also forms one of the points of the widespread Summer Triangle. Yet summer isn’t the only time to see Deneb in the evening sky. As Earth turns on its axis, the distant stars return to the same position in the sky every 23 hours and 56 minutes. If you’re quick with numbers, you’ll notice that’s four minutes shorter than the length of a day. That’s because as Earth moves in its orbit around the Sun, the viewing angle to the Sun changes just slightly. So it takes four minutes longer for the Sun to return to the same spot in the sky compared to the other stars. And that means the other stars rise and set four minutes earlier each day. So Cygnus will be a little higher in the sky at the same hour tomorrow night than tonight. By autumn, it’ll be high in the south at nightfall. And by winter, it’ll be in the west, with its beak pointing down toward the horizon. At that angle, the swan’s outline looks like another shape, giving Cygnus a second name: the Northern Cross. More about Cygnus tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Pegasus, the flying horse, is beginning its climb into the evening sky. It clears the eastern horizon by about 11 p.m. It’s preceded into the sky by another horse, which is to the upper right of Pegasus. Equuleus is far smaller and less prominent than its famous equine cousin. In fact, of all the constellations passed down from the ancient world, it’s by far the smallest — you can cover all of it with your palm held at arm’s length. Unlike most ancient constellations, there’s not much of a story associated with Equuleus. And as it’s drawn in the sky, it’s not even a full horse — only a head, which is outlined by a lopsided rectangle of four meager stars. The brightest is Alpha Equulei, which is actually a pair of stars locked in a tight orbit around each other. Both stars are about twice as massive as the Sun, with one just slightly heavier than the other. That difference in heft has made a big difference in the lives of the two stars. The heavier one has already ended its “normal” lifetime, and is entering one of its final stages. That’s caused the star to puff up like a balloon. The smaller star is still in the prime of life. Yet as the bigger star puffs up, the surfaces of the two stars may get so close that the stars begin to swap some of their gas — a process that may alter the evolution of both stars. Equuleus is in the east at nightfall. It’s below Delphinus, the dolphin — another small constellation, but one that’s much easier to pick out. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A star and an onion might not seem to have much in common. But as the heaviest stars near the ends of their lives, they’re put together a lot like an onion. All stars begin their lives by “fusing” together atoms of hydrogen in their cores to make helium. When they’ve used up all the hydrogen they can, gravity squeezes their cores more tightly, making them hotter, so they fuse the helium to make carbon and oxygen. For stars like the Sun, that’s as far as it goes — they can’t get hot enough to make heavier elements. But stars that are at least 8 to 10 times the mass of the Sun can. Gravity squeezes them much more tightly, allowing the carbon to fuse to make neon and other elements, which takes a few thousand years. It then takes just a few years for the neon to make oxygen, and a few months for the oxygen to make silicon. Each of these steps leaves a layer of the earlier elements, creating the onion-like structure. The final step takes just a few days. The silicon fuses to make iron. The iron can’t fuse to make heavier elements, so the reactions stop. With no energy to resist the pull of gravity, the core collapses, creating a shock wave that blasts away the onion-like layers around the dead core as a supernova. One star that will undergo that fate is Antares, which is to the lower right of the Moon as night falls. It’s probably fusing helium in its core right now, so the clock is ticking toward its demise — sometime in the next million years. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Although the Sun is a star, just like all those twinkling points of light in the night sky, not many stars closely resemble it. Most stars are much fainter than the Sun, while a few are much brighter; most stars are cooler, while a few are hotter; and most stars are a good bit younger or older. But a few stars are near twins to the Sun, including one that’s visible in the southwestern sky tonight: 18 Scorpii, which is faintly visible to the unaided eye. Astronomers in Brazil reported the star’s remarkable similarity to the Sun in 1997. They found that its light output was nearly identical to the Sun’s, as were its color, temperature, and mass. It’s also about the same age as the Sun, with a similar abundance of heavy, planet-forming materials, so it could have a planetary system like ours. So far, no one has actually discovered planets orbiting 18 Scorpii, but the search continues. And if any planets orbit the star at about the same distance that Earth is from the Sun, conditions could be just right for life. 18 Scorpii is just 45 light-years away, so it’s visible to the unaided eye — if you have a dark sky and know just where to look. As darkness falls tonight, it’s high above the lineup of the Moon and the beautiful orange star Antares to its left or lower left. A good star map should show you the way from Antares to 18 Scorpii — a near neighbor to our Sun in more ways than one. We’ll have more about the Moon and Antares tomorrow. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Mid-summer may not be the best time for a steaming cup of tea, but that’s just what the night sky offers at this time of year. The brightest stars of Sagittarius, which is low in the southern sky at nightfall, form the outline of a teapot. And the hazy Milky Way seems to form puffs of steam from its spout. The puffs are a combination of bright stars and gas and dark clouds of dust in the disk of the Milky Way galaxy. And if you look deeply into those puffs you’ll see quite a few other little puffs of matter — star clusters and the vast clouds known as nebulae. Two famous ones are directly above the spout, by about the width of your fist held at arm’s length — the Lagoon Nebula and the Trifid Nebula. The Lagoon is a stellar nursery — a cloud of gas and dust dozens of light-years across. It’s given birth to scores of stars, with more taking shape even now. Through binoculars or a small telescope, it looks like a hazy oval of light. Photographs show a reddish-pink glow, which is the color of hydrogen atoms being zapped by the radiation of young stars. The Trifid is also a hot-pink stellar nursery, but with a different appearance. Dark lanes of dust across its center make it look like three different blobs. There’s also a nearby cloud of dust that reflects starlight, so it glows blue instead of pink. Look for these beds of starbirth immersed in the steam rising from the celestial teapot, low in the south on warm summer nights. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

One of the brightest stars in the night sky snuggles close to the first-quarter Moon tonight. Spica, the leading light of the constellation Virgo, is to the right of the Moon at nightfall. Equally brilliant Saturn is about the same distance to the upper right of Spica. Although Spica looks like a single pinpoint of light, it’s actually the combined glow of two stars, each of which is quite impressive in its own right. The system’s primary star is more than 10 times as massive as the Sun and about 12,000 times brighter. The second star is about six or seven times as massive as the Sun, and about 1500 times brighter. On its own, it would still be visible to the unaided eye, but just barely. The two stars are only a few million miles apart, so from Spica’s distance of 250 light-years, their light blurs together. But that close proximity has more profound effects on the stars themselves. Their gravitational pull on each other is so strong that the stars puff out toward each other, giving each of them a “bulge” on one side. When the stars align so that these bulges are visible from Earth, Spica’s overall brightness increases by a tiny bit. The brightness of the primary star also varies a bit because the star pulses in and out like a beating heart. So Spica’s light flickers like a light bulb with a slightly bad connection — the flickering of two brilliant stars. Tomorrow: A steaming cup of starlight. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A compact box of four bright astronomical objects stands in the southwest at nightfall this evening. The Moon anchors the rectangular box. The planet Mars is close to the upper right of the Moon, with the star Spica and the planet Saturn to its upper left, forming the other side of the rectangle. All four objects are bright enough to see well before the end of twilight — the colorful result of sunlight interacting with the atmosphere. You’d also see twilight on Mars. In fact, twilight there lasts up to two hours — a bit longer than the typical twilight on Earth. That’s because the Martian atmosphere is filled with dust — tiny grains of sand lofted by the Martian winds. The dust grains absorb most of the blue wavelengths of sunlight and scatter redder wavelengths. That makes the daytime sky look pink or orange. Much of the sky stays pink as the Sun sets, although the region around the Sun looks blue. The dust extends many miles above the surface. So well after the Sun sets, its rays are still illuminating dust grains high above the Martian nightside. That prolongs the twilight — keeping the Martian skies aglow with color well after sundown. Again, look for Mars — which is colored orange by the same dust that colors its sky — quite close to the Moon this evening. By tomorrow evening, the Moon will have left Mars behind, and will stand closer to Spica and Saturn. We’ll have more about that on our next program. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Perhaps the most famous star in the night sky is Polaris. It’s not especially bright or close by. Instead, it’s famous for its location. It marks the north celestial pole, so it’s also known as the North Star or the Pole Star. Right now, it’s about two-thirds of a degree from the true celestial pole. But over the next century, it’ll snuggle even closer. The change is caused by a slow “wobble” in Earth’s rotation. Over a period of 26,000 years, that causes the planet’s axis to draw a big circle on the sky. So while Polaris itself will still be around, it won’t keep its position as the North Star. The axis is sweeping counterclockwise. So the next moderately bright star it’ll point to is Gamma Cephei, which is to the right or lower right of Polaris as darkness falls this month. It’ll take over as the North Star in about 3,000 years. After moving past another star of Cepheus, the pole will take aim at Deneb, the “tail” of Cygnus, the swan, around the year 10,000. And 3500 years later it’ll be the brightest pole star of all, Vega. Neither Deneb nor Vega will be all that close to the true celestial pole, but their brilliance will make up for the gap. And in about 20,000 years, the pole will come around to Thuban. It marked the pole about 4,500 years ago, when it helped architects align the pyramids of Giza. Finally, around the year 28,000, the pole will return to Polaris — closing its great circle on the sky. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Like a chick that’s left the nest, the Sun moves through the galaxy alone. But many of the galaxy’s stars are still in their nests — in great clusters of hundreds of stars. All the stars in a cluster are members of the same brood — they were all born from the same giant cloud of gas and dust. Two examples are near the tail of Scorpius, which is low in the south at nightfall. The brighter one is M7, which is to the left or upper left of the two stars that represent the scorpion’s stinger. Under moderately dark skies, it’s visible to the unaided eye as a tight knot of stars. Binoculars reveal more stars, and telescopes reveal still more. From the types of stars the cluster contains, astronomers deduce that M7 is about 200 million years old — only about five percent the age of the Sun. That youthfulness is one reason the cluster is still together. As a cluster orbits the center of the Milky Way, the combined gravity of the galaxy’s other stars gently pulls it apart, sending its stars off on their own. The other cluster, M6, is to the upper right of M7. It’s farther than M7, so it doesn’t look as big or bright. In fact, you need pretty dark skies to see it without optical aid. With optical aid, the colorful stars of M6 form a pattern that resembles the outline of a butterfly. M6 is also young, so its stars are also still tightly bound together by their own gravity — keeping the nest full for a little while longer. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The celestial scorpion packs a mighty sting — the two stars that mark its “stinger” are quite impressive. Scorpius is low in the south at nightfall, with its brightest star, orange Antares, near its middle. The tail curls to the lower left of Antares, forming a hook with the barbed stinger at the end. The brighter of the stinger stars is Lambda Scorpii. It’s actually a system of three stars. Two of them are hot giants that are thousands of times brighter than the Sun. They’re also much more massive than the Sun. In fact, one of them may be massive enough to end with a titanic explosion — a supernova. Either way, both stars are nearing the ends of their “normal” lifetimes and soon will enter their final phases. Lambda Scorpii’s third star may be on the other end of the age scale — an infant that hasn’t yet settled into stellar maturity. If so, it’ll outlive its siblings by millions or billions of years. Upsilon Scorpii forms the stinger’s tip. It’s more than 500 light-years away — half again as far as Lambda. Yet indications are that it’s a single star, which makes it impressive indeed — about 12,000 times brighter than the Sun. It’s a similar mass to the two older stars of Lambda. But it appears to be a little bigger, which is why it shines so brightly. It, too, may end its life as a supernova — adding a little more zing to the scorpion’s sting. We’ll talk about some stars that are close to the stinger tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The lion’s bright heart is dropping from view in the evening sky. The star Regulus is low in the west by nightfall, and sets not long after. It’ll drop lower in the sky each evening, and disappear from view within a few weeks. More than two millennia ago, Regulus was just climbing into view in the morning sky at this time of year. That appearance may have served as a marker for several cities in the ancient world, including Alexandria. Alexander the Great, who was born on or near today’s date in the year 356 BC, established Alexandria on the Mediterranean coast of Egypt. The city was intended not only as a tribute to Alexander, but as a symbol of his power and his rightful place in the cosmic order. In fact, a recent study by two architecture professors in Italy suggests the city layout was based on two celestial alignments. The alignment of Alexandria’s original main road didn’t follow the natural contours of the land, suggesting that there was another reason for it: paying tribute to Alexander. That’s because the road points at the sunrise on the date of Alexander’s birth. That’s also the point where Regulus first became visible in the dawn sky. And in the ancient world, Regulus was the star of kings. The study found that several later cities in the region also seemed to align with Regulus — bolstering the idea that the star of kings helped glorify the achievements of Alexander — the greatest king of his day. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.