StarDate Podcast

The Moon’s gravity pulls on the water in Earth’s oceans. That creates “bulges” in the oceans that move as Earth rotates on its axis, creating the daily cycle of high and low tides. Tides aren’t limited to planets and moons, though — they’re also found on stars. In fact, a good example is a star system that keeps company with the last-quarter Moon late tonight: Spica, the leading light of Virgo. It’s to the lower left of the Moon as they rise in the wee hours, and to its left at first light. Spica actually consists of two stars, each of which is much bigger, brighter, and heavier than the Sun. They’re so close together that they orbit each other once every four days. At that range, each star exerts a powerful gravitational pull on the other. That pull is strongest on the sides of the stars that face each other, just as the Moon’s pull is strongest on the side of Earth that faces it. The difference in the gravity on the two sides of each star causes the stars to bulge toward each other. As a result, the stars are slightly egg-shaped, with the tapered ends pointing at each other. We can’t see this effect directly because the stars blur together to form a single point of light. But we can see it indirectly. As the two stars orbit each other, we see them from different angles. When we look at the system from the side, where the bulges are most obvious, Spica grows a tiny bit brighter — the result of giant tides on giant stars. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Most of what we see in the night sky is neat and orderly. We know exactly where the stars and planets will appear centuries in advance. We know when eclipses will occur, and where best to view them. And we can spool out the phases of the Moon far into the future. Yet the night sky still offers some unpredictable treats. In fact, two are coming up this year — we think. Both of them are comets — big balls of rock and ice that sprout long, glowing tails when they get close to the Sun. One is scheduled to put on its best showing in the early evening skies of mid-March, when it’s expected to be bright enough to see with the unaided eye. The other will be at its best in November. But if early predictions are correct, it could be the brightest comet in centuries — perhaps shining bright enough to see during the day. Both comets were discovered just last year. And both are probably making their first close approach to the Sun. Their paths indicate they’re heading inward from the far edge of the solar system. Comets are notoriously fickle, though, so it’s hard to predict just how brightly they’ll shine. The November comet will pass less than a million miles from the surface of the Sun, so it could become truly spectacular. Or as it nears the Sun it could disintegrate, leaving nothing to see. Or it could do something in between — something that adds a bit of disorder — and a lot of fun — to the night sky. We’ll keep you posted. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The year’s first meteor shower should be at its best in the hours before dawn tomorrow. The Quadrantids “rain” into the atmosphere from the extinct constellation Quadrans Muralis, which is fairly close to the handle of the Big Dipper. The Quadrantids may be the spawn of an asteroid, which in turn could be the dead remnant of a comet. Comets are balls of frozen water and gases mixed with rock. They’re left over from the birth of the planets. In fact, the planets probably formed as many of these iceballs stuck together to form larger and larger bodies. But hundreds of billions of iceballs remained. Many were hurled into interstellar space by the gravity of the giant planets. Others were thrown into distant orbits around the Sun. Occasionally, one of these gets a gravitational nudge — or a bump from one of its kin — and heads toward the Sun. As it nears the Sun, some of its outer layers of ice vaporize. That releases water vapor and other gases into space, along with small grains of rock. They form a giant cloud around the comet’s nucleus. And the Sun’s radiation and magnetic field push some of this material away from the comet, forming a long, glowing tail. As a comet loops close to the Sun, it leaves a trail of rocky debris. And if Earth happens to fly through this path, then we see a meteor shower — the calling card of a comet. A couple of comets are expected to put on good displays in this year’s night skies. More about that tomorrow. Script by Damond Benningfield For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The new year begins with fire and ice in the sky. For fire, there’s the Sun, which is at its closest to Earth for the entire year. And there’s more fire in the night sky — a meteor shower — but its source is a ball of ice: a comet. The part about the Sun doesn’t seem right at this time of year, which has the coldest days and longest nights in the northern hemisphere. Yet late tonight, Earth will snuggle closest to the Sun for the year — about a million-and-a-half miles closer than the average distance of 93 million miles. The change in seasons is caused not by the changing distance to the Sun, but by Earth’s tilt on its axis. Right now, the north pole is tipped away from the Sun, so the northern hemisphere gets less solar energy. And late tomorrow night, the year’s first meteor shower should reach its peak — the Quadrantids. Its fiery “shooting stars” all appear to “rain” into the atmosphere from an extinct constellation, not far from the handle of the Big Dipper. But they can streak across any part of the sky, so you don’t have to look in a particular direction to see them. The best view comes before dawn on Thursday. The Quadrantids may come from a small asteroid, which may in turn be the remnant of a dead comet — a ball of ice and rock that shed bits of debris as it neared the Sun. When Earth plows through this debris, it rains into the atmosphere, creating meteors — fiery lights from a ball of ice. More about comets tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

As the clock strikes midnight tonight, many will light up the sky with fireworks. But it’s hard to beat the light show offered by the sky itself. The view is especially impressive away from city lights. But there are enough bright stars and other objects to shine through even from most cities. The most prominent object is the Moon. It was full just four days ago, so it’s still big and bright. Regulus, the brightest star of Leo, the lion, is close to its left. Sirius, the brightest star in all the night sky, is well up in the south. It twinkles fiercely, changing color from red to blue to pure white. And if you’re in the southern tier of states, you can also see the second-brightest star, standing below Sirius — Canopus, the luminary of Carina, the keel. Orion, the hunter, shines to the upper right of Sirius. Its most prominent feature is its “belt” of three closely spaced stars. The hunter’s brightest stars are above and below the belt, forming the corners of a big box. Jupiter, the largest planet in the solar system, blazes high in the southwest. It looks like a brilliant cream-colored star. It outshines everything else in the sky at that hour except the Moon, so you can’t miss it. And it has a bright companion — Aldebaran, the orange “eye” of Taurus, the bull. So if you have a chance, take a break from the holiday festivities to appreciate the beauty of the night sky — an ever-changing light show that’s on display all year long. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Sun and similar stars are steadily losing weight — they blow some of their gas into space through strong “winds.” And at the end, they blow away their entire outer envelopes of gas, leaving behind only their hot, dense cores, known as white dwarfs — tiny remnants of their once glorious selves. An example is Sirius B, the faint companion to Sirius A, the brightest star in the night sky. Sirius climbs into view in the east-southeast by around 8:30 or 9, and arcs across the south during the night. Sirius B is too small and faint to see without a telescope. But millions of years ago, that wouldn’t have been the case. The star probably was a few times as massive as the Sun, so it would have shined many times brighter — brighter than Sirius A is today. Such a hot, bright star produces a much thicker wind than the Sun does, so it loses mass at a higher rate. And because the star was heavier than the Sun, it burned through the nuclear fuel in its core much faster — it burned out in a couple of hundred million years, while the Sun is still only half way through a 10 billion-year lifetime. As it neared the end of its life, Sirius B puffed up like a giant balloon, then ejected its outer layers. Some of that gas probably piled on the surface of Sirius A, increasing its mass. Today, Sirius B is as heavy as the Sun, but only as big as Earth. It still shines because it’s extremely hot. But it’s only a dim remnant of its former glory. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Over the centuries, we’ve given all the visible stars many names — proper names, catalog designations, and others. But only one star is best known not by any of its formal names, but by its nickname: the Dog Star. Its proper name is Sirius, and it’s the leading light of the constellation Canis Major, the big dog — hence the nickname. Sirius is so well known because it’s the brightest star in the night sky — its closest competition is only about half as bright. Part of that is because Sirius itself is a couple of dozen times brighter than the Sun. But part of it is because Sirius is one of our closest neighbors — it’s less than nine light-years away. And thanks to the relative motions of Sirius and the Sun around the center of the galaxy, Sirius is moving closer, at about 17,000 miles per hour. It’ll continue to close in on us for tens of thousands of years. But the distances between stars are so enormous that even at that high rate of speed, Sirius won’t grow much brighter in our sky. Astronomers discovered the star’s motion toward us by measuring its Doppler shift — a slight change in the wavelength of its light. The Doppler shift also allowed them to measure the orbit of a faint companion — a stellar corpse known as a white dwarf; more about that tomorrow. In the meantime, look for Sirius climbing into good view in the east-southeast by around 8:30 or 9. It’s the brightest star in the night sky, so you can’t miss it. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Orion, the hunter, strides boldly across the southern sky on winter nights. The big, bright constellation is low in the east shortly after nightfall, with its famous “Belt” of three bright stars pointing up from the horizon. Orion’s brightest star, blue-white Rigel, is to the right of the Belt, representing the hunter’s foot. A mighty foot can get mighty tired, so long-ago skywatchers gave Orion a convenient footstool to rest it on — a pattern of four relatively faint stars that’s above Rigel in early evening. The brightest member of the group is known as Cursa, from an Arabic name that means “footstool of the Central One.” It marks the western end of the winding constellation Eridanus, the river. Like many of the stars that are visible to the unaided eye, Cursa is a stellar giant. It’s nearing the end of its “normal” lifetime, so it’s beginning to puff up, getting brighter as it does so. So even though it’s almost 90 light-years away, the fact that it’s bigger and brighter than the Sun makes it easy to see. As Cursa undergoes a series of changes in its core, it’ll grow even bigger and brighter. Then it’ll blow its outer layers off into space, leaving behind only its hot but dead core — a white dwarf. Over the eons, that remnant will slowly cool and fade away, shifting the course of the meandering celestial river. Watch Orion as it climbs across the south during the night, with the footstool rotating below the hunter’s bright foot. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

This is a great night for werewolves and other lunaphiles in the northern hemisphere. That’s because it’s the night of the Long-Night Moon, when the full Moon is in view longer than any other full Moon of the year. The full Moon lines up opposite the Sun in Earth’s sky, so it does just the opposite of what the Sun does in the daytime sky. Since the winter solstice — the shortest day of the year — was just a few days ago, the Sun is still putting in its most feeble appearances of the year. It rises late, sets early, and scoots low across the south during the short day. So the full Moon does just the opposite — it rises around sunset, climbs high across the sky during the night, and sets around sunrise. The difference is more dramatic at more northerly latitudes. San Antonio, for example, will see about three hours and 45 minutes more moonlight than sunlight. But from Seattle, the difference is more than seven hours — eight-and-a-half hours of sunlight, followed by 15-and-a-half hours of moonlight — a long night to watch the silvery glow of the full Moon. And as you watch the Moon, look for some bright companions around it. The brilliant planet Jupiter is high above it in early evening, flanked by the star Aldebaran, the ruddy “eye” of Taurus, the bull. And a star that looks like a near twin to Aldebaran, Betelgeuse, is closer to the right or lower right of the Moon — adding to the beauty of a winter’s night. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Until recently, planetary scientists thought the Moon was bone dry, with not a drop of water anywhere. They still haven’t found any drops of water, but they have found water molecules spread across much of the Moon. And one of the ingredients for much of that water may come from the unlikeliest of places: the Sun. When Apollo astronauts brought samples of lunar rock and soil back to Earth, scientists found no trace of water in any of them. But in recent years they’ve analyzed more of the samples with techniques that weren’t around back in the 1960s and ’70s. These studies have revealed water molecules embedded in tiny beads of glass. At the same time, orbiting spacecraft have detected the chemical “fingerprint” of water mixed with the powdery dirt across much of the lunar surface. And spacecraft have also detected large amounts of water ice at the Moon’s south pole. The polar water may come from comets that have slammed into craters that never see sunlight. But a recent study says that much of the rest of the water forms when hydrogen in the solar wind rams into the lunar surface. Some of the hydrogen links up with oxygen in the dirt to form water or another compound, known as hydroxyl. So the hot Sun and the dry Moon work together to produce water molecules across the lunar surface. The Moon is low in the east as darkness falls this evening. The brilliant planet Jupiter stands to its upper right, with the star Aldebaran close to Jupiter. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

This is the coldest, darkest time of year for the northern hemisphere. The days are shortest, and the Sun scoots lowest across the sky. In ages gone by, many cultures tried to lure the Sun back with lights of their own — big bonfires outdoors, or big hearthfires indoors. Some of this tradition of light has carried over into the modern celebration of Christmas, with Yule logs, candles, and in today’s world, twinkling electric lights as well. And on this Christmas night, the Sun compensates a bit for its daytime absence by lighting up two brilliant night lights: the Moon and the planet Jupiter. Both shine not by producing their own light, but by reflecting sunlight. The Moon is the same distance from the Sun as Earth is, so each square foot of the lunar surface receives the same amount of sunlight as the same area on Earth. Jupiter is five times farther from the Sun, though, so the same area of its surface receives much less sunlight. Not one-fifth as much, as you might expect, but one twenty-fifth. That’s because at Jupiter’s distance, the sunlight has spread out. So the same amount of sunlight that falls on one square foot of Earth or the Moon spreads out to cover 25 square feet on Jupiter. And the light that Jupiter reflects also spreads out as it heads toward us. Even so, there’s plenty of light to make Jupiter the third-brightest object in the night sky — and a beautiful decoration for Christmas night. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Long before the last blush of twilight fades away on this Christmas Eve night, two brilliant objects blaze into view in the east: the gibbous Moon and, to its lower left, the planet Jupiter. They arc high across the south during the night, drawing ever closer to each other as they do so. Although they’re the two brightest objects in the sky for most of the night, neither the Moon nor Jupiter actually shines on its own — they don’t produce light like the bulbs on a Christmas tree. Instead, they shine by reflecting sunlight. The Moon reflects very little sunlight — only about 10 percent, give or take. That means its surface is quite dark. But it’s so close to Earth that it forms a big disk in our sky, so there’s a lot of visible surface to reflect sunlight our way. Jupiter is close to 2,000 times farther than the Moon, so it forms a much smaller target. But it’s the largest planet in the solar system, and it’s topped by bright clouds that reflect close to half of the sunlight that strikes them. So Jupiter shines brilliantly — only the Moon and the planet Venus are brighter. One other bright object stands to the lower right of Jupiter: Aldebaran, the orange “eye” of Taurus. Although it looks fainter than Jupiter, that’s only because it’s farther away. Aldebaran is a giant star — one that’s much bigger and brighter than the Sun. But its light is dimmed by its great distance: more than 65 light-years. More about this bright lineup tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

One of the most prominent constellations of summer skies transforms itself when the weather turns cold. It’s still the same pattern of stars, but because of the different viewing angle, it’s often seen as a different picture. The constellation is Cygnus, the swan. During the summer months, it soars high across the evening sky, when more people are paying attention to the stars. Its brightest stars form a pattern that reminds many of a graceful bird, with a long neck and widespread wings. By this time of year, though, Cygnus is in the western sky during the evening hours. Its beak points downward, with its wings roughly parallel to the horizon, as though it’s plunging toward the ground. Seen at this angle, it more closely resembles the constellation’s nickname — the Northern Cross. The star at the top of the cross represents the tail of the swan — blue-white Deneb. It’s one of the biggest, brightest, hottest stars in our region of the galaxy. Although there’s some wiggle room in the distance, it’s probably close to 1,500 light-years away. That means the light we see from Deneb tonight has been crossing the Milky Way galaxy for a millennium and a half — a long-distance trek from a star that anchors two star patterns. Look for Cygnus — the Northern Cross — standing well up in the west as night falls, and perching directly atop the horizon in mid-evening. Tomorrow: bright lights for Christmas Eve night. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

If you’re dreamin’ of a White Christmas, you don’t have to stay on Earth to find it. Snow also appears to fall on Mars. And you might even find some snow on Venus — not on its hellish surface, but in a layer of clouds about 75 miles high. The Venus Express spacecraft has found evidence of that layer during its five years in orbit around our closest planetary neighbor. It found that a high-altitude layer of clouds is quite cold — cold enough for carbon dioxide to freeze and form small ice grains or snowflakes. Even if they exist, though, the snowflakes won’t get anywhere close to the surface. For one thing, they’re sandwiched between cloud layers that are hundreds of degrees warmer. And even if they could get through those clouds, Venus’s surface temperature is more than 850 degrees Fahrenheit — an environment where you’re not likely to hear any sleigh bells in the snow. Mission scientists are continuing to study the results to confirm the finding, and to learn what might be causing the cool-down high above the planet. Venus is in view in the dawn sky right now, blazing forth as the brilliant “morning star.” The star Antares, the leading light of Scorpius, is close to its lower right tomorrow. They’re so low in the sky that Antares is tough to see through the early twilight, but its proximity to Venus will help you pick it out. Venus is sliding down toward the Sun, so it’ll stand side by side with Antares on Wednesday. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

One calendar cycle comes to an end today as another begins. This magical moment is the December solstice, when the Sun stands farthest south in the sky for the entire year. It marks the end of autumn and beginning of winter in the northern hemisphere. You probably know that another calendar cycle is coming to an end today as well — the Maya cycle known as 13 baktun. According to some mystics and authors, Mayan prophecy said the end of that cycle would also mark the end of the world. And over the last couple of decades, an industry has sprung up to support that idea, offering theories about hidden planets and other disasters. None of it, of course, is supported by the facts. There was no Mayan prophecy of doom. Instead, the end of a baktun was seen as something like the end of a millennium in the modern calendar — a time when the calendar simply resets with a lot of extra zeroes in it. The Maya were good observational astronomers. They followed the motions of the Moon and the planet Venus, and developed tables that allowed them to predict the appearance of either one in the sky. Certain appearances of these objects were seen as good times to crown kings and launch wars. But nothing in the Mayan calendar foretold the end of the world. And there’s no deadly planetary alignment, no galactic energy rays, and no killer planet headed our way, either. It’s just a day like many others before it — a day in which one cycle ends and another begins. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.