StarDate Podcast

One of the reddest stars in the galaxy bounds across the south on February evenings, hidden in the “fur” of Lepus, the hare. Its primary name is R Leporis, but it’s better known as Hind’s Crimson Star for the astronomer who discovered it in the 19th century. The star looks so red for a couple of reasons, both of which are related to its age. Hind’s Crimson Star is in the final stages of life, so its outer layers have puffed up to giant proportions — about 75 times the Sun’s diameter. That’s caused its outer layers to get cooler, so they shine reddish orange. At the same time, a lot of carbon has been dredged from the star’s interior and pulled to the surface. The carbon absorbs blue light, which enhances the star’s red color. Some of the carbon, along with other elements, is being blown into space by a strong “wind” from the surface of the star. This wind is much thicker than the wind from the surface of the Sun. And it’s a first step in the star’s demise. Eventually, the star’s outer layers will all blow out into space, forming a glowing bubble. Over tens of thousands of years, the bubble will spread out and vanish from sight. After that, only the star’s hot core will remain — a tiny stellar corpse known as a white dwarf. Lepus is in the south as night falls, below the feet of Orion. Hind’s Crimson Star is too faint to see with the eye alone. But a small telescope reveals its rich red color — the color of a dying star. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

As darkness falls this evening, the zodiac arcs high across the southern sky, with Orion, the hunter, just below this famous band of stars. Under dark skies, it’s a grand view. But from places like New York City, it’s much less grand — overpowered by the glow of city lights. Fortunately for New Yorkers, though, they can see that panorama anytime they want — on the ceiling of Grand Central Terminal. The railroad station opened to the public 100 years ago today. It was one of the wonders of its time — an $80 million model of efficiency and technology. It was also a grand work of art, from its ornate exterior to its astronomical ceiling. The ceiling was conceived by architect Whitney Warren and French artist Paul Helleu. The design was based on illustrations from a medieval atlas — which caused a bit of consternation: Like the pictures in the atlas, the stars on the ceiling are backwards. The ceiling includes the outlines of six constellations of the zodiac, plus Orion — the same swath of sky that’s visible this evening. They were painted in gold leaf on a background of cerulean blue. Small light bulbs illuminated the 60 brightest stars — replaced today by LEDs. The ceiling had to be replaced in the 1930s. And it was fully restored with the rest of the terminal in the 1990s. Workers removed a layer of cigarette smoke that had darkened the sky. The clean up allowed the zodiac to shine brightly above New Yorkers — but only from inside Grand Central Terminal. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Moon and a couple of bright companions put in a good showing at dawn this weekend. And for the Moon, the show doesn’t end there — it continues for most of the morning. As twilight begins to paint the sky tomorrow, the star Spica stands close to the right of the Moon, with the planet Saturn a bit farther to the upper left of the Moon. By Sunday, the Moon will have moved eastward in its orbit around Earth, so both Spica and Saturn will be to its right. As the twilight waxes, Saturn and Spica will wane, eventually fading from view — hidden in the glare of the daytime sky. The Moon will fade as well, but unlike its companions, it won’t disappear — it’ll remain in view until it sets in late morning. In fact, over the course of its month-long cycle of phases, the Moon spends just as much time in the daytime sky as in the nighttime sky. The Moon commands the night because it’s thousands of times brighter than just about any other astronomical object. But in the daytime sky, it’s a pale second. The Sun is about 400,000 times brighter than the full Moon, and a million times brighter than tomorrow’s gibbous Moon. And the blue glow of the daytime sky itself is much brighter than the dark of the night sky, so the Moon doesn’t stand out. Once you notice the Moon in the daytime sky, though, you’ll wonder why you didn’t see it before — moving wanly across the Sun’s domain. Tomorrow: the night sky in the daytime sky. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Black holes should be the ultimate contestants at hide-and-seek. After all, their surface gravity is so strong that not even light can escape them, so they really are completely dark. Yet that gravitational pull also frequently gives them away. Just as fields of flowers attract bees, black holes attract gas. As the gas spirals toward a black hole, it gets extremely hot, so it shines brightly — especially in X-rays. And that gives the black hole away. In fact, astronomers have used X-ray telescopes in space to discover four likely black holes in M31, the Andromeda galaxy. M31 is high in the west at nightfall, above the Great Square of Pegasus. Under dark skies, it’s visible to the unaided eye as a small, hazy patch of light. The new black holes are all in globular clusters — densely packed balls of old stars. Some theories have suggested there shouldn’t be any black holes in such clusters, because they’d get kicked out by gravitational interactions with other stars. Yet the X-ray objects found in M31’s clusters can’t be explained by anything other than black holes that are ingesting large amounts of gas — gas stolen from companion stars. All the black holes are likely a few times as massive as the Sun, although one could be 30 times the Sun’s mass. That means they’re all the collapsed cores of once-mighty stars. So while the black holes are completely dark, they’ve given themselves away — by taking gas from their companions. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The black holes that form from collapsed stars are stories in contradiction. They’re small but heavy. They have a surface, but it’s not something you could touch. And they can be both completely dark and overpoweringly bright. Astronomers have been studying an example of that last contradiction in M31, the Andromeda galaxy. They discovered an object that produced more X-ray energy than the rest of the galaxy combined. Yet that energy came from a tiny region of space — a region encircling a black hole. The object is known as an Ultraluminous X-ray source. It was discovered in 2009 by an X-ray telescope in space. Since then, astronomers have watched with several space telescopes as the object slowly faded a bit. The X-rays came from a disk of superhot gas around a black hole that’s about 13 times as massive as the Sun. The black hole is “stealing” gas from a fairly average companion star. So much gas was spiraling in that the black hole couldn’t swallow it all, so the gas piled up. This logjam caused the gas to get hotter and hotter, so it emitted huge amounts of X-rays. Eventually, something broke the logjam. Perhaps the X-rays blew some of the infalling gas away from the black hole, or perhaps something else happened. Whatever the case, the X-rays faded a bit. But such outbursts tend to repeat, so the object in M31 may one day flare up again as the black hole gorges itself on gas from its companion. More about M31 tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

M31, the giant Andromeda galaxy, is a near twin to our own galaxy, the Milky Way. Both are spiral galaxies, and they’re about the same size and mass. And each has a supermassive black hole at its center. The black holes themselves aren’t exactly twin-like — the one in Andromeda is probably 10 to 20 times as massive as the one in the Milky Way. But the environments around the black holes are similar — each is encircled by a cluster of bright young stars. Astronomers recently confirmed the cluster at the center of M31. It spans several light-years, and contains hundreds of stars. Many of those stars are hotter and brighter than the Sun, indicating that they’re also more massive than the Sun. Such stars can’t be very old. In fact, the cluster may be just 100 million to 200 million years old, compared to an age for the overall galaxy of more than 10 billion years. The cluster may have formed when a giant cloud of gas collapsed around the black hole, breaking up into smaller clumps that made individual stars. Today, these stars provide a bright contrast to M31’s dark heart. M31 is in good view on winter evenings. Tonight, it’s about two-thirds of the way up the western sky at nightfall, not far from the upper right corner of the Great Square of Pegasus. Under dark skies, it’s visible to the unaided eye as a small, hazy smudge of light — the light of a galaxy that’s much like our own. More about M31 tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Galileo Galilei is already known as one of the greatest astronomers in history. With his handmade telescopes, he discovered the four largest moons of Jupiter and the phases of Venus. He found that the Milky Way actually consists of countless individual stars, and saw that instead of being smooth, as just about everyone thought, the Moon was covered by jagged mountains, valleys, and craters. Yet if he’d realized what he was looking at 400 years ago today, Galileo might have burnished his reputation even more. He recorded a small star near Jupiter, which had moved relative to the other stars around it. This pinpoint of light was the planet Neptune, which wasn’t officially discovered until 1846. Galileo was fascinated by the moons of Jupiter. He’d been watching them for a couple of years, charting their positions and even predicting their motions. And in January 1613, Neptune crept behind Jupiter, sliding across Galileo’s field of view. His notebooks show that he actually recorded the planet three times over several weeks. It was at a point where it doesn’t move much against the background of stars, so its position relative to the true stars didn’t change by a lot. One researcher has suggested that Galileo knew he was looking at a possible planet. But Galileo never announced his finding to the rest of the world. Since he kept the mysterious “star” to himself, Neptune remained “undiscovered” for more than two centuries. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Modern depictions of Greek and Roman mythology tend to sanitize things a bit — less blood and gore, more ear-catching tunes. A prime example is Hercules, the Roman version of Heracles. In the Disney telling of the story, he fights a bunch of monsters, then earns immortality by being willing to sacrifice himself to save his true love. But in the original version of the story, he has to fight the monsters because he killed his own wife and children. The story says that he killed them after he was driven mad by his stepmother, Hera, the queen of the gods of Olympus. As atonement, Hercules must complete 12 herculean feats of strength and courage. The first of these labors was to kill a lion that was terrorizing the people of Nemea, and take its skin to the king. But the lion’s skin couldn’t be pierced, so Hercules’s arrows just bounced off it. So the strongman followed the lion to its lair. He blocked one of its two entrances, then entered the cave. When Hercules found the lion, he grabbed it in a mighty choke-hold, eventually strangling it. He then used the lion’s own claws to skin it. Afterwards, Zeus, the king of the gods, placed the lion in the heavens, as the constellation Leo. And Leo is in great view tonight, spreading out near the Moon. The lion’s bright heart, the star Regulus, is not far to the lower left of the Moon as they climb into good view around 8 or 9 o’clock, and remains close as they spring across the sky during the night. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

A giant ring of bright stars dominates the southern half of the sky on winter nights. It includes the brightest star in all the night sky, plus the leading lights of several well-known constellations. And tonight, it’s easier to pick out than usual because it’s bracketed by two brilliant objects: the full Moon and the planet Jupiter. Jupiter outshines all the other planets and stars in the sky for most of the night, so you can’t miss it. The hub of the great Winter Circle is a little south of the line that connects Jupiter and the Moon: Betelgeuse, the orange shoulder of Orion, the hunter. Brilliant Sirius, the brightest star in the night sky, is almost directly below Betelgeuse as darkness falls, twinkling fiercely in the southeast. And the other bright stars of the circle extend about the same distance from Betelgeuse, with Capella at the top. They include the twins of Gemini, the eye of Taurus, and the foot of Orion. And they shine in different colors — white, yellow, orange, and blue. The full Moon actually helps the Winter Circle stand out a bit, because its light overpowers the glow of the fainter stars. Only the really bright ones stand out — like those of the multi-colored Winter Circle. And by the way, the Moon is officially “full” at 10:38 p.m. Central Standard Time. It’s known as the Wolf Moon, Old Moon, or Moon After Yule — or tonight, the Moon That Follows the Winter Circle. More about the Moon tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The human eye is finely tuned to see a narrow range of wavelengths — a range of colors from deep red to deep blue. Yet there’s an entire universe beyond those extremes — from wavelengths that are just a thousandth as long as the eye can see, to wavelengths that are a million times longer. The longer side begins with the infrared. It’s produced by some of the coolest objects in the universe — objects like clouds of gas and dust that are giving birth to new stars. But they’re difficult to study from Earth’s surface because the atmosphere absorbs most infrared energy. The first major attempt to extend our view into the infrared began 30 years ago today, with the launch of IRAS — the Infrared Astronomy Satellite. When it was launched, astronomers had discovered about 250,000 objects in the infrared. During its 10 months of operation, IRAS doubled that number. It also provided details on those objects that were impossible to see from the ground — details like temperature and composition. And it provided the most detailed pictures of these objects, allowing us to see their structure. IRAS studied newborn stars, disks of gas and dust that are giving birth to planets, dusty galaxies, and icy comets. Those observations helped astronomers learn more about how stars and planets are born, and how galaxies evolve — new knowledge made possible by extending our vision into a new realm. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

One of the smallest planets yet discovered around a “normal” star isn’t likely to be a popular destination for future star travelers. The planet is smaller than Earth, but it’s only a couple of million miles from its parent star. At that distance, its surface temperature is more than a thousand degrees Fahrenheit — so hot that the surface may be coated with molten rock. The planet orbits the red-dwarf star Gliese 436, which is far smaller, fainter, and cooler than the Sun. Its surface is so cool that it emits most of its light in the infrared. Infrared wavelengths are tough to see from Earth because they’re absorbed by the atmosphere. So scientists were studying the star and another known planet with Spitzer Space Telescope, which is sensitive to the infrared. Spitzer detected tiny dips in the star’s brightness. Astronomers realized those dips were caused by a planet passing in front of the star, briefly blocking some of its light. From that, they were able to measure the planet’s size, mass, and its distance from the star — compiling a thorough dossier with the help of infrared light. Infrared provides the best views not only of cool stars, but of the gas clouds that are giving birth to stars, the cocoons of dust that are giving birth to new planets around stars, and many other objects. And the best way to study them all is with space telescopes. In fact, the first infrared space telescope was launched 30 years ago. More about that tomorrow. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Sun is a pretty sedate star — which is a good thing for life on Earth. It bathes us in life-giving light and heat. But it doesn’t zap us with the titanic explosions of energy seen on many other stars. The Sun does produce outbursts known as solar flares. These eruptions can knock out orbiting satellites and trigger blackouts on the ground. But recent observations by the Kepler spacecraft show that some stars launch superflares up to 10,000 times more powerful than any solar flare ever seen. Kepler’s main task is to find planets that pass in front of their parent stars, blocking a bit of the star’s light. But because the craft is so sensitive to changes in stellar brightness, it can also detect superflares. Japanese scientists studied Kepler observations of more than 83,000 stars that are similar to the Sun. During a four-month period, about 150 of these suns launched at least one superflare strong enough to damage the ozone layer of an Earth-like planet and produce a mass extinction. Most of the superflares came from stars that spin much faster than the Sun does. Rapid rotation intensifies a star’s magnetic field, generating dark starspots and powerful flares. When the Sun was younger, it probably spun faster, too, so it may have produced its own superflares. Today, the Sun spins slowly, so its magnetic storms are much less intense than those seen on other stars — keeping us safe from these stellar catastrophes. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Today, the Sun races around the galaxy with only its planets in tow. But when the solar system was forming, it was a different story. The Sun had lots of company then — it was a member of a cluster of more than a thousand stars. And one of those stars exploded quite close to the newborn Sun. Evidence for this “flashy” neighbor comes from meteorites — space rocks that have fallen to Earth. Most meteorites formed when the solar system itself did, so they’re time capsules that preserve the conditions that prevailed just before Earth was born. By analyzing meteorites, astronomers have concluded that a massive star likely exploded less than one light-year from the young Sun. That’s only a quarter of the distance to what’s now the closest star system, Alpha Centauri. When a massive star explodes, it hurls radioactive debris into space. Some of the radioactive elements from the neighboring supernova splattered the solar system and became embedded in chunks of rock. Over time, these elements decayed into other elements, altering the chemistry of compounds in the rocks. An explosion so close to home may have changed the structure of the solar system, making it easier to produce a planet like Earth. And it tells us that the Sun was born in a large cluster, because the heavy stars that explode as supernovae form only in such clusters. So a flashy neighbor helped mold our current neighborhood — and provided long-lasting clues to how it happened. Script by Ken Croswell, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Two worlds that have taken a beating stage a spectacular encounter in tonight’s sky. The Moon will swing quite close to the planet Jupiter, which shines like a brilliant star. The Moon’s most prominent features are its impact basins. They formed billions of years ago, when giant asteroids slammed into the Moon. The basins filled with molten rock, forming the dark volcanic plains we see today. Yet the Moon also carries the scars of much smaller impacts, which form craters. These have formed throughout the Moon’s lifetime. You won’t find an impact crater anywhere on Jupiter, because the planet is a ball of gas, with no solid surface. But like the Moon, it continues to get hit. And its composition makes those impacts stand out — but only for a while. The most spectacular impacts came almost two decades ago, when the remnants of a fractured comet hit Jupiter like a cosmic hailstorm. But the aftermath of several smaller impacts have been seen over the last few years. When space rocks slam into Jupiter’s upper atmosphere, they explode. That stirs up material from below the planet’s cloud tops, forming dark splotches. Strong high-altitude winds sweep these blotches into long streaks that can last for days or weeks. Jupiter is the largest planet in the solar system, and it has the strongest gravity, so it’s a big target for asteroids. They continually pound the planet — they just don’t leave long-lasting scars for us to see. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Sirius, the brightest star in the night sky, rotates across the south on winter evenings. It’s low in the southeast at nightfall, and it’s hard to miss. Not only is it especially bright, it’s also especially twinkly — it shifts from blue to red to pure white in the blink of an eye. Sirius is visible from most of Earth’s surface — all but the high Arctic. But the second-brightest star has a more limited range. Canopus is a stunner from the southern hemisphere, but here in the northern hemisphere, it’s tough to see. You have to be south of about Los Angeles or Atlanta to find it. And even then it never climbs more than a few degrees above the horizon. Canopus itself is quite a bit more impressive than Sirius. It’s far larger and more massive, and about 500 times brighter. But it’s also close to 300 light-years farther, so it can’t quite match Sirius’s luster. Canopus is at the end of its “normal” lifetime, so it’s quite puffy — if it took the Sun’s place in our own solar system, it would extend all the way out to Mercury. But no one is quite sure whether it’s getting even bigger, or if it’s starting to “deflate” after going through a puffier phase not long ago. Either way, Canopus will continue to shine brightly in Earth’s night sky — even if not everyone can see it. If you’re far enough south, look for Canopus quite low in the south beginning around 9 o’clock. It’s due south around 10 or 11, almost directly below Sirius. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.