StarDate Podcast

The night sky is filled with circles, triangles, and all other manner of geometric figures. In fact, like the skywatchers of old, you can draw your own figures by connecting different groups of bright stars. And if you look in the west at nightfall at this time of year, one pattern you’re almost certain to see is a big square or diamond standing high in the sky. It won’t be a new picture, though — it’s the Great Square of Pegasus, which has been around for more than 2,000 years. Alpheratz stands at the highest point of the square, and it’s the brightest of the square’s four stars. Through a quirk of modern mapmaking, though, it’s no longer officially a member of the constellation Pegasus. In the 1930s, astronomers drew precise boundaries for all 88 constellations. Under this system, Alpheratz is just across the border from Pegasus, in Andromeda. Indeed, it’s Andromeda’s brightest star. Alpheratz is actually two stars, not one. The one that’s visible to us is bigger, brighter, and heavier than the Sun. It’s also near the end of its “normal” lifetime, so it’s getting ready to puff up like a big balloon. The star at the opposite corner of the square, Markab, is similar to Alpheratz, and it’s in about the same phase of life. It looks a little fainter than Alpheratz mainly because it’s several dozen light-years farther. Markab stands below Alpheratz as they drop toward the western horizon and set in late evening. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

There’s a lot of elbow room out in our region of the Milky Way galaxy. The nearest star system is four light-years away, and only a few dozen stars are within 15 light-years. If the Sun were in the middle of a star cluster in the constellation Gemini, though, our night skies would be a lot busier, with perhaps 2500 stars or more within 15 light-years. Many of those stars would outshine any of the stars that are visible in our current skies, so it would be a spectacular sight. M35 is in the east at nightfall, at Gemini’s feet — well to the upper right of its “twins,” the stars Castor and Pollux. Although the cluster is more than 2500 light-years away, under dark skies it’s visible to the unaided eye as a fuzzy blob of light. Binoculars enhance the view, and small telescopes reveal many of the cluster’s individual stars. M35 is only about 150 million years old. Yet that’s plenty of time for the cluster’s hottest, heaviest stars to have expired. Some may have blasted themselves to bits, while others cast their outer layers into space in a more gentle process, leaving behind their hot, dense cores. That’s also long enough for many of the cluster’s original stars to have been pulled away by the gravity of the rest of the galaxy. But M35’s remaining stars are bound together so strongly by their mutual gravitational pull that they’re likely to stay together for a long time — keeping a crowded stellar neighborhood intact. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Understanding the stars is all about models. Astronomers build mathematical models to explain how stars generate energy, how they evolve, and how they die. The models make predictions about a star’s brightness, its temperature, its size, and other parameters. So to verify how well the models work, astronomers compare their predictions to measurements of real stars. Consider the star Epsilon Geminorum. It’s in the constellation Gemini, which is in the east in early evening. Epsilon Geminorum is well to the right of Gemini’s brightest stars, the “twins” Castor and Pollux. A technique called photometry reveals a star’s temperature by measuring its color. Epsilon Geminorum is yellow-orange, so it’s fairly cool. And astronomers get a star’s true brightness by comparing its distance to how bright it looks in the night sky. Epsilon is about 900 light-years away, so it’s thousands of times brighter than the Sun. The Moon periodically passes in front of Epsilon, blocking it from view. Measuring how long it takes to disappear behind the Moon reveals the star’s size. Astronomers also measure the size by combining the view from several telescopes, which produces ultra-sharp images. These techniques reveal that Epsilon Geminorum is about 150 times the Sun’s diameter, making it a supergiant. All of these numbers match the models quite well — showing that astronomers have a pretty good grasp on how the stars work. We’ll talk about a star cluster tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

There’s no formula for predicting how long a person will live. Genetics, nutrition, exercise, and other factors all play a role, but you can’t just plug in a couple of numbers and come up with an exact lifespan. But that’s not the case with the stars. A single number determines how long a star will live: its mass. An example of how it works is in good view on winter nights: Pollux, the brightest star of Gemini. It’s in the east at nightfall, below its slightly fainter “twin,” Castor. Pollux is almost twice as massive as the Sun. And that number makes all the difference in its lifespan. Pollux is roughly half as old as the Sun. But it’s already finished its “normal” lifetime — the phase the Sun is in right now. During that normal lifetime, a star “burns” the hydrogen in its core to make helium. When the hydrogen is gone, the core gets smaller and hotter, so it begins to burn the helium to make carbon and oxygen. At the same time, its outer layers puff up like a balloon, making the star much brighter. That also makes the star’s surface much cooler, so it glows reddish-orange, as Pollux does now. Over time, Pollux will get even bigger and brighter. Then it’ll expel its outer layers, briefly surrounding itself with a colorful bubble of gas. That bubble will quickly fade, though, leaving only the star’s small dead core — a hot ember known as a white dwarf. The same fate awaits the Sun — several billion years in the future. More about Gemini tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The star Castor represents one of the twins of Gemini. But it takes the business of “twinhood” to extremes. Although we see it as a single point of light, Castor actually consists of three sets of stellar twins — a total of six stars in all. All six stars in the system really are related, because they were born from a single giant cloud of gas and dust, probably around 200 million years ago. Two pairs of Castor’s twins are more fraternal than identical. One star in each pair is a good bit bigger, brighter, and heavier than the Sun, while the other star in each pair is smaller, fainter, and less massive than the Sun. The stars in each pair are so close together that they orbit each other in just a few days. At such close range, there’s no way for telescopes to see them as individual stars. Instead, special instruments separate the “fingerprints” of the stars as they go around each other, providing details on each star. The third set of Castor twins is identical. Each star is smaller, cooler, and less massive than the Sun, and much fainter. And while the other two sets of twins are relatively close to each other, this set is so far away that it takes thousands of years to orbit the others — a set of twins that keeps its distances from its brighter siblings. Castor is low in the eastern sky at nightfall, not far above Gemini’s other twin, Pollux. Castor is slightly fainter than Pollux, and shines pure white. More about Pollux tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Ancient skylore is pretty tawdry. Everywhere you look, you find stories of betrayal, seduction, vanity, and even murder. Yet some skylore is a bit more uplifting — tales of love, devotion, and sacrifice. One of those tales is told in the story of Castor and Pollux — the twins of Gemini — who climb high overhead on winter nights. According to the most common version of the story, the queen of Sparta gave birth to two sets of twins — one boy and one girl in each pair. One set was fathered by her husband, the other by Zeus, king of the gods. The four children were raised together, and the two boys — one mortal, the other immortal — were inseparable. They had many adventures, and joined Jason and the other Argonauts in the search for the golden fleece. But during a fight with some landowners, the mortal Castor was killed. Pollux was inconsolable, and eventually begged Zeus to allow him to die so he could join Castor. Moved by Pollux’s love for his brother, Zeus agreed to keep them together for eternity. They spend half of their time in the underworld, the other half in the heavens — where they’re represented by the stars of Gemini. The constellation is in the east as night falls this month. Its two brightest stars represent the twins themselves, with slightly fainter Castor above Pollux as they rise. The rest of Gemini stretches to their right as two streamers of moderately bright stars. We’ll have more about Gemini tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Phobos, the larger moon of Mars, could be one of the solar system’s most exciting thrill rides. But if you’re not careful, it could become a little too thrilling — one big push and you’d float off into space. Phobos is a lumpy boulder that’s only about 15 miles in diameter. Its main feature is a giant impact crater. The impact that gouged it was so strong that it almost blasted the moon to bits. Phobos orbits just 3700 miles above the Martian surface. At that altitude, it moves so quickly across the Martian sky that it rises in the west and sets in the east, with moonrises about 11 hours apart. Seen from Phobos, Mars would span about a quarter of the sky, and its surface would slide past you at about a thousand miles per hour. So in a single circle around Mars — daylight permitting — you’d see everything from the giant volcanoes of the Tharsis Ridge to Valles Marineris, a complex of canyons that dwarfs the Grand Canyon here on Earth. But because of Phobos’s low altitude, you wouldn’t see Mars’s polar ice caps — they’d be hidden around the curve of the planet itself. You wouldn’t want to get too excited by the view, though. The gravity of Phobos is so weak that a single big jump would launch you into space — leaving the Martian moon behind. Mars is in our own sky right now, quite low in the west-southwest as twilight begins to fade. It looks like an orange star. And this evening, it’s well below the crescent Moon. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The crescent Moon and the planet Mars are quite low in the western sky as twilight fades away, and set not long after the sky gets good and dark. Mars looks like a moderately bright orange star to the upper left of the Moon. The Moon probably formed after another planet slammed into the young Earth, spewing debris into space. Much of that material coalesced to form the Moon — and perhaps several moons; the others fell back to Earth or merged with the one moon we have today. The same process may also have given birth to the moons of Mars. Phobos and Deimos are lumpy boulders only a few miles across. That led to speculation that they are asteroids that were somehow captured when they wandered close to Mars. Catching an asteroid is a tricky process, though, so many scientists questioned that scenario. And today, the “capture” idea has given way to a different model: that Phobos and Deimos formed from the debris from an impact between Mars and a smaller body. The case isn’t closed, though — scientists continue to debate the origins of these tiny moons. But their fates are clear. Deimos is slowly inching away from Mars. Phobos, on the other hand, is inching toward Mars — by about an inch a year, in fact. Eventually, it’ll either slam into Mars or be pulverized before it hits, forming a ring around the planet — a ring similar to the one that may have given birth to the tiny moon. More about the moons of Mars tomorrow. Script by Damond Benningfield For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Cancer, the crab, scuttles high across the sky on January nights. It’s not that much to look at — a sprinkle of faint stars between Gemini and Leo. One of those stars is quite a treasure, though. It has at least five planets, making it one of the busiest planetary systems outside our own. And one of those planets may be made largely of diamond. The planet is 55 Cancri E. It’s a good bit bigger and heavier than Earth. A recent study said that as much as a third of it may be made of diamond, with diamonds as common on the surface as granite is here on Earth. In part, that’s because the parent star contains a lot of the raw ingredient for diamonds: carbon. Adding high heat and pressure transforms it into its crystalline form: diamond. 55 Cancri E is far from the biggest diamond out there. An object that orbits a pulsar appears to be a diamond about 35,000 miles in diameter — the core of a once-normal star that was stripped of almost all its mass by the neutron star. And a smaller but heavier stellar core forms an even more massive diamond — one that’s about two-thirds the mass of the Sun. The core is a white dwarf — the last remnant of a once-normal star like the Sun. This small, dense stellar corpse is made of carbon and oxygen. Over a couple of billion years, its center cooled enough for the carbon to crystallize — forming the biggest diamond yet discovered. The core of the Sun may become a diamond as well — billions of years from now. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

According to Russian scientists, vast beds of diamonds lie beneath the floor of an impact crater in Siberia. Instead of the “girl’s-best-friend” variety, though, they’re industrial grade — good for manufacturing, not so much for ring fingers and earlobes. In a way, all diamonds are cosmic in origin. They’re made of carbon, which is forged inside stars and expelled into space when the stars die. Earth incorporated carbon from stars that had died long before its birth. Most of the diamonds on Earth formed far below the surface, where high temperatures and pressures transformed carbon into its crystalline form. But some diamond formed when large asteroids slammed into our planet, instantly transforming carbon to diamond — carbon that was already here on Earth, or that was in the rock that hit Earth. Tiny diamond grains have been found in the fragments of the asteroid that created Barringer Meteor Crater in Arizona, for example. The Russian crater formed about 35 million years ago, when an asteroid a few miles in diameter gouged a crater that’s about 60 miles across. The impact could have generated enough energy to create a large bed of diamonds. In some cases, meteorites arrive with bits of diamond already inside. These small grains may have been created in supernova explosions, when shock waves heated and compressed carbon in the outer layers of the exploding stars — a fiery birth for tiny bits of “ice.” More about diamonds tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The days have been getting longer since the winter solstice three weeks ago. The extra daylight has all been tacked on to the end of the day. Sunrise has continued to come a little later each day for much of the United States. The Sun is just now beginning to reverse that trend and rise a little earlier. For skywatchers, the benefit of that arrangement is that you don’t have to get up all that early to enjoy the delights of the dawn sky. Tomorrow is a good example, with the Moon and the planet Venus quite low in the sky at first light. Venus is the brilliant “morning star,” to the right of the crescent Moon. The combination of Venus and the Moon shining through the early blush of twilight paints a beautiful tableau. Another beautiful aspect of the view is the non-crescent portion of the Moon — the part of the lunar surface that’s not bathed in sunshine. It still shines through, though, because it’s bathed in earthshine — sunlight reflected off our own planet. That light makes the bulk of the Moon look like a ghostly apparition framed by the crescent. That light comes from an almost-full Earth suspended in the lunar sky, shining so brightly that it would almost hurt to look at it. In fact, Earth will be full as seen from the Moon on Friday, when the Moon is new — it crosses between Earth and Sun, and is hidden in the Sun’s glare. It’ll return to view by Sunday, this time as a thin crescent in the early evening sky. Script by Damond Benningfield For more skywatching tips, astronomy news, and much more, read StarDate magazine.

An astronomical troublemaker will pass just a few million miles from Earth early tomorrow. Planetary scientists will keep a close eye on it to see if there’s any chance at all of it causing real trouble in a couple of decades. The asteroid was discovered in 2004. Early measurements of its orbit indicated there was a small chance it could hit Earth in 2029. So its discoverers named it Apophis for a pair of mythological troublemakers — an Egyptian god of darkness and destruction, and the main bad guy in the early seasons of the TV series “Stargate: SG1.” Since then, the asteroid has spawned a legion of doom-and-gloom web sites. Apophis’s orbit crosses Earth’s orbit, so Apophis periodically passes close to our planet. Tomorrow, for example, it’ll be less than nine million miles away. And it’s big enough that if it were to hit us, it would cause widespread devastation. Soon after its discovery, though, better tracking of its orbit ruled out any chance of an impact in 2029. But it left a tiny chance of an impact seven years later — less than one in a hundred thousand. The longer astronomers look at Apophis, the more accurately they can predict its exact location in the future. So each time the asteroid is in good view, it’s being tracked by both optical and radio telescopes. Those continuing observations are expected to rule out any chance of an impact in the next few decades — holding an astronomical troublemaker at bay. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The surface of a star looks like a pot of boiling water. Giant bubbles of hot gas rise from deep inside the star, carrying heat to the surface. But there are bubbles, and then there are bubbles. On the Sun, for example, these bubbles — known as convection cells — are typically as big as Texas. On the biggest stars around, though, the cells can be hundreds of times bigger than the Sun. These stars are known as red supergiants, and a prime example is in good view the next couple of mornings. Antares, the bright heart of Scorpius, is below the Moon at first light tomorrow, and to the right of the Moon on Wednesday. Antares is one of the most impressive stars in the galaxy. It’s around 15 times the Sun’s mass, hundreds of times the Sun’s diameter, and when you combine all wavelengths of light, tens of thousands of times brighter. Its core is much hotter than the Sun’s as well, so there’s a lot of heat that’s trying to escape. It does so in the form of giant convection cells. Antares is so far away that it’s almost impossible to see these cells. But computer simulations show that they may come in a couple of sizes. The little ones are perhaps 50 times wider than the Sun, and last for a few months. The big ones are a couple of hundred times the Sun’s diameter. These giants last for years, and as they cool, they may plunge all the way to the star’s core — where they heat up and once again bubble back to the surface of this giant star. Script by Damond Benningfield For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Most of the stars that are visible in the night sky are youngsters — most are no more than a few billion years old, while some are still in the millions of years. But many of the galaxy’s stars are as old as the Milky Way itself — more than 12 billion years. A whole bunch of those old stars congregate in a globular cluster known as M2. It’s low in the west at nightfall, in the constellation Aquarius. It’s not quite bright enough to see with the eye alone, but binoculars show it as a small, fuzzy blob of light. The cluster is about 35,000 light-years away, and it spans more than 200 light-years. It contains perhaps 150,000 stars, all of which are less massive than the Sun. When it was born, M2 probably contained lots of big, bright stars as well. But such stars burn out in a hurry. All that’s left are the smaller stars, which consume their nuclear fuel much more slowly than the heavier ones. In fact, astronomers determine the cluster’s age by looking at the masses of the stars that are in the final stages of life. Heavier stars have already expired, while lighter ones are still in the prime of life. The stars that are just now expiring are roughly as massive as the Sun. Models of how stars evolve show that those stars are about 12-and-a-half billion years old — which tells us that that’s also the age of the entire cluster. That makes the stars of M2 some of the oldest in the galaxy. Tomorrow: a star on the heavy end of the scale. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

It certainly wasn’t the most destructive storm of last year’s hurricane season, but it was the most tenacious. Nadine meandered across the eastern Atlantic Ocean for more than three weeks, waxing and waning in strength and eventually looping back on itself before finally vanishing. It was one of the longest major storms on record. On the solar system’s giant outer planets, though, storms rage not for weeks, but for months or even years. An example is a storm that flared to life more than two years ago in the northern hemisphere of Saturn. Within weeks, it had wrapped all the way around the planet. And that’s quite a distance, because Saturn is more than nine times Earth’s diameter. The storm remained visible for months. Even after it vanished from view, though, it was still going. Instruments aboard the Cassini spacecraft recorded a giant “hotspot” where the storm had been seen. Temperatures in this region were up to 150 degrees Fahrenheit hotter than the surrounding clouds. The hotspot contained large amounts of ethylene and acetylene — hydrocarbons that probably formed through chemical reactions in Saturn’s turbulent atmosphere. The hotspot — and the giant storm — finally faded last year. Saturn itself is in good view early tomorrow. It’s to the left of the Moon at first light, and looks like a bright golden star. It’s a world where giant storms are common — storms that keep on going even after they vanish from view. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.