StarDate Podcast

A giant star that teased astronomers into thinking it had exploded three years ago finally blasted itself to bits last year. When the star produced a mammoth eruption in 2009, astronomers designated it as Supernova 2009ip. Within days, though, they had second thoughts. The explosion faded too quickly for a true supernova, and the material it blasted into space was moving too slowly. Astronomers realized the star had duped them. After a similar outburst a year later, 2009ip staged a third eruption last July. It remained bright for weeks, and the ejected material was traveling at a few percent of the speed of light. In other words, this outburst really was a supernova. Pictures snapped over a period of about 10 years before the final explosion revealed that the star was a luminous blue variable. Such stars are dozens of times as massive as the Sun and a million times brighter. 2009ip is the first confirmed instance of such a star exploding as a supernova. Astronomers aren’t sure what caused the earlier outbursts. One possibility is a reduction in the radiation pressure in the star’s core, which keeps the core from collapsing. Another is the ignition of nuclear reactions in different layers around the core. Either process could mimic a supernova - and fool astronomers into thinking the star had blasted itself to bits. The blast probably left behind a tiny, crushed core known as a neutron star. More about neutron stars tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

If it’s been a nasty winter where you are, then you have our sympathy. On the bright side, though, it’s almost over - spring arrives in the northern hemisphere early tomorrow. Now that doesn’t mean the weather conditions will change overnight. The shift of the seasons is a long, slow process, not something that happens with the flip of a switch. It’s governed by the leisurely progression of the Sun across the sky, which in turn is the result of the changing angle between the Sun and Earth’s poles. At the start of spring - the vernal equinox - the Sun crosses the equator from south to north. Neither pole dips toward the Sun, so the entire planet will see roughly equal amounts of daylight and darkness. Over the next three months, though, as Earth continues in its orbit around the Sun, the north pole will gradually dip toward the Sun. That will bring longer, warmer days to the northern hemisphere, and shorter, cooler ones to the southern hemisphere. It’ll also bring non-stop sunshine to the north pole - a “day” that will stretch almost six months from sunrise to sunset. One other item of note is that the Sun rises due east and sets due west on the equinox. That’s not the case at other times of the year. As the Sun moves northward across the sky, its rising and setting points move northward, too. So the equinox is a good time to get your bearings right here on Earth - all part of the constant progression of the seasons. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Moon passes close to the tip of one of the horns of Taurus this evening. It’ll slip within a few degrees of Zeta Tauri, the star that marks the bull’s eastern horn. The other horn, El Nath, will stand to their upper right as night falls. Zeta Tauri is much larger, heavier, and hotter than the Sun. The combination also makes it much brighter than the Sun, so it’s easily visible even though it’s more than 400 light-years away. A disk of gas and dust surrounds Zeta Tauri, blown into space from the star’s surface. The dust grains form as atoms in that thick stellar wind link together to form solid particles. They absorb some of the star’s light. As they do so they warm up, so they emit their own glow, in the infrared. El Nath looks brighter than Zeta Tauri, but that’s because it’s only about a third as far as the bull’s other horn. In fact, El Nath is only a few percent as bright as Zeta Tauri. It, too, is bigger and more massive than the Sun, but not as big as Zeta Tauri. Both stars are nearing the ends of their lives. As they age, they will puff up to giant proportions and shine far brighter than they are now. Millions of years later, they’ll shed their outer layers, leaving behind only their dead cores, known as white dwarfs. Those stellar corpses will be as heavy as the Sun, but only as big as Earth. They’ll still shine because they’ll be extremely hot. But over the eons, they’ll radiate their heat into space, ending their days as dark cosmic ash. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The Moon slides between two bright companions this evening - the planet Jupiter and the star Aldebaran, the “eye” of Taurus, the bull. They’re in grand view as night falls, and set in the wee hours of the morning. If you keep an eye on them during that period, you’ll get a good illustration of how quickly the Moon moves across the sky. It takes four weeks for the Moon to circle through the background of stars. So from one night to the next, the Moon moves a little more than the width of your fist held at arm’s length. That’s a pretty good distance, but it’s hard to see it during the night because there aren’t always bright stars or planets around to measure the Moon against. Tonight, though, there are two good markers. Jupiter is by far the brighter of the two. In fact, after the Moon itself, it’s the brightest object in the evening sky right now. Aldebaran is only a few percent as bright, but it’s still one of the brightest true stars, so you won’t have any trouble finding it. The exact Moon-Jupiter-Aldebaran configuration depends on your location. But the trio will remain in view for several hours after sunset. During that time, the Moon will move about six times its own diameter. With the other bright objects so close by, that distance is pretty obvious to even the most casual of skywatchers. So if you have the chance, keep tabs on the Moon throughout the evening, as it continues its eternal eastward slide across the sky. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Most of the stars in the Milky Way galaxy more or less go with the flow - they orbit the center of the galaxy in the same direction and at about the same speed as the stars around them. But a few follow their own paths. An example is a star at the tip of the Guitar Nebula - a big bubble in space whose outline resembles a guitar. It’s in Cepheus, the king, which is low in the north on March evenings. The constellation’s brightest stars form an outline that resembles a child’s drawing of a house. Don’t look for the nebula, though, because it’s so faint that it wasn’t discovered until 1992. It was sculpted by a pulsar - the crushed core of a once-mighty star. It spins once every two-thirds of a second, emitting a pulse of energy with each turn. The pulsar was born when the star exploded as a supernova. The explosion must have been off-center, so it gave the dead core a powerful kick. The pulsar is plowing through clouds of gas and dust at more than a million miles an hour. It leaves an expanding wake behind it, like a boat traveling across the ocean. That wake is what we see as the Guitar Nebula. But there’s more to the nebula than what we can see. X-ray telescopes reveal a long, high-speed “jet” of material squirting away from the tip of the nebula. The jet most likely is powered by the pulsar’s magnetic field, which funnels material away from the pulsar - adding another interesting note to a celestial guitar. More about pulsars tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The swallows are coming back to Capistrano. A celebration kicks off next week at the mission in San Juan Capistrano, where the little birds have migrated for decades. Another visitor from above descended on the California town 40 years ago today: a meteorite - a rock from beyond Earth. It crashed into the aluminum roof of a carport and split apart. The owners found the biggest piece the next morning on the floor of the carport. They found a much smaller piece about a month later while cleaning the gutter. The pieces didn’t add up to much - only about two ounces in all. But the meteorite represents a treasure to scientists, because it helps them understand more about the early solar system. The San Juan Capistrano meteorite is classified as a chondrite. That means it contains small bits of rock that melted then resolidified long ago. Chondrites probably formed at the same time as Earth and the other planets of the solar system. As a result, they may reflect the composition of the original cloud of dust from which the planets formed - four and a half billion years ago. This meteorite is especially valuable because it was picked up within hours of landing, so scientists know it hadn’t been changed by exposure to Earth’s atmosphere. It should preserve a good sampling of the materials present at the birth of the planets - an important scientific gift that descended on a California town. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

If the pictures you snap with your cell phone just aren’t sharp enough for you, you may want to invest in a new camera like one that’s about to start hunting for dark energy. The camera’s images are 570 megapixels, providing amazingly sharp images of the night sky. There are a couple of drawbacks, though - the camera’s the size of a phone booth, and it cost millions of dollars. The camera is the centerpiece of the Dark Energy Survey, which will attach the camera to a four-meter telescope in Chile. The project will use several techniques to study dark energy - a mysterious force that appears to make the universe expand faster as it ages. Astronomers are trying to find out whether it’s a form of energy created by space itself, a flaw in our understanding of gravity, or something else entirely. The camera will snap pictures of hundreds of millions of galaxies and thousands of exploding stars. Those observations will reveal how fast the universe was expanding at different times in its history. They should also reveal a pattern in the way galaxies are distributed in the sky - a pattern established in part by the influence of dark energy. The camera took its first pictures in September and became operational last month. But the Dark Energy Survey won’t begin until fall, when the part of the sky it’ll study is in good view. Until then, the camera is available for use on other projects - projects that will benefit from giant pictures of the sky. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

One of the most remarkable objects that’s visible to the unaided eye stands well up in the south-southeast as night falls: the Orion Nebula. It looks like a small, fuzzy patch of light below the three stars of Orion’s Belt. Yet it’s really a spectacular stellar nursery - a complex of thousands of newborn stars, plus the gas and dust for making many more. The nebula is a prime target for a new telescope that’s being dedicated today in Chile. It’s called ALMA - the Atacama Large Millimeter-Submillimeter Array. When it’s completed, it’ll consist of 66 large radio dishes scattered across a three-mile-high plateau in the Andes Mountains. A supercomputer will combine the signals from the dishes to produce images and other observations of a variety of astronomical objects. Many of those objects involve gas and dust, which glow brightly at ALMA’s wavelengths. The list of targets includes stellar nurseries like the Orion Nebula, star systems where planets are taking shape, and the gas clouds around black holes. ALMA will also study the chemistry of interstellar space, putting together a list of the ingredients available to make new stars and planets. Right now, only about half of ALMA’s antennas are hooked up, and astronomers are already using them to study the universe. But the view will get a lot better when the full array is online next year - providing clearer views of some dusty parts of the cosmos. We’ll talk about another new telescope project tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

When a star explodes as a supernova, it’s bad news for any planets that orbit it. The shockwave and radiation rip the planets apart, leaving nothing more than puffs of debris. As things settle down, though, some of that debris may coalesce to make new planets - desolate chunks of rock orbiting the supernova’s dead core, known as a neutron star. In fact, astronomers have discovered planets orbiting two neutron stars. The stars spin rapidly, emitting bursts of energy with each spin, so they’re also known as pulsars. The time between pulses of energy is like the tick of an ultra-precise clock. But the gravitational pull of an orbiting planet changes the length of each tick by a tiny amount, revealing the planet’s presence. The first pulsar planets were discovered more than two decades ago - the first planets discovered around any star other than the Sun. All three planets in the system are no bigger than Earth. A second pulsar system consists of a planet orbiting the pulsar and a companion star. Another small object has been discovered around a third pulsar. Although it’s sometimes described as a planet, it was born as a star. But the supernova and the extreme radiation from the pulsar have eroded all but its carbon core. Today, it’s basically a chunk of solid diamond orbiting its violent companion. Astronomers study these systems with radio telescopes. And they’re getting ready to dedicate a giant new radio telescope in Chile. More about that tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The brilliant planet Jupiter is slowly pulling away from the face of Taurus, the bull. The bull’s orange eye, the star Aldebaran, is to the lower left of Jupiter at nightfall. The other stars of the bull’s V-shaped face are members of a stellar family known as the Hyades cluster. It’s closer than any other cluster, so it’s a popular target for study. Among other things, astronomers have looked for planets orbiting the stars of the Hyades. They haven’t found any, but they have found evidence of a planetary system around a dead star known as a white dwarf. A white dwarf is the collapsed core of a once-normal star. Its surface and atmosphere consist of hydrogen and helium. But a white dwarf in the Hyades shows evidence of calcium in its atmosphere. The calcium can’t come from the star itself, so it must come from outside. The most likely source is asteroids - large boulders that are some of the building blocks of planets. Encounters with other objects may fling some of the asteroids toward the white dwarf. When they get close enough, they’re pulverized by the star’s gravity. They form a ring of debris, which eventually settles on the surface of the white dwarf. In fact, about one in five white dwarfs shows evidence of “pollution” from asteroids. Most of this debris matches the composition of Earth - suggesting that worlds that are made much like our own are common throughout the galaxy. We’ll have more about exoplanets tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Most astronomers don’t pay a lot of attention to the stars known as red dwarfs. They’re the smallest and faintest stars known, and they don’t change much, so they don’t have a lot of sex appeal. But when it comes to the hunt for habitable planets, these cool stars are a hot topic. To support life as we know it, a planet must be small and rocky, like Earth. And it must be at the right distance from its star to have liquid water on its surface. But finding such planets is difficult. The techniques that astronomers use to reveal Earth-like planets in Earth-like orbits take a lot of time, and the indications of such planets are small and hard to detect. Since red dwarfs are so small, though, they offer advantages in the planet-hunting derby. For one thing, the signature of an Earth-like planet that orbits a red dwarf is much larger. And for another, such a planet would be quite close to the parent star, so each orbit would take only a few weeks or months, which also makes detection easier. And there are a lot more red dwarfs than other types of stars. In fact, red dwarfs account for at least three-quarters of all the stars in the entire galaxy. So that gives astronomers a lot of targets. Searches of the three closest red dwarfs - Proxima Centauri, Barnard’s Star, and Wolf 359 - have yet to discover any planets at all, much less planets in the “habitable zone.” Yet the searches continue - for comfortable worlds around feeble stars. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

The discovery of a new “exoplanet” doesn’t generate a lot of excitement these days. That’s because astronomers are discovering planets in other star systems at an astonishing pace. The number of confirmed planets is getting close to a thousand. And just a couple of months ago, scientists with the Kepler mission announced the discovery of almost 500 more possible planets. Astronomers will use ground-based telescopes to try to confirm the discoveries. Today, much of the excitement isn’t over individual new planets. Instead, it’s about what the large numbers reveal about how all planets form - and what percentage of planets might be suitable for life. One thing the numbers tell us is that planets like to move around. Many planets are so close to their parent stars that they must have been born much farther out and then migrated inward. The planets might move inward as the result of friction with gas and dust leftover from the birth of the planets, or through gravitational interactions with other planets. How many planets are suitable for life is still uncertain. A habitable planet would have to be at the right distance for liquid water, and it would have to be small and rocky, like Earth. Searches haven’t revealed many worlds that fit that profile. In part, though, that’s because it takes longer to find such worlds. But it should be easier to find habitable worlds around one particular class of stars. More about that tomorrow. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

If you looked up in your sky today and saw four suns, you’d probably be hallucinating - unless you lived on a planet that was recently discovered in observations by the Kepler spacecraft. Designated PH1, the planet is a giant world that belongs to a quadruple star system. The planet orbits a closely bound pair of the stars every four and a half months. One of the stars is much brighter than the other. In fact, the yellow-white star is brighter than the Sun. But its companion star is just the opposite. It’s a faint cosmic ember known as a red dwarf - a star that’s much smaller, lighter, and fainter than the Sun. But there are two more stars in the distance, about 30 times farther from PH1 than Pluto is from Earth. Depending on where the planet is in its orbit around its two main suns, these two distant stars can appear during the day, during the night, or during both - just as our Moon sometimes appears during the day, the night, or both. Remarkably, this planet wasn’t found by professional astronomers. Instead, it was discovered by a couple of amateurs. They were analyzing Kepler data on their home computers as part of a project called Planet Hunters, which is open to anyone who wants to join. So the planet’s name - PH1 - stands for “Planet Hunters One.” Despite the somewhat dull name, though, PH1 is an extraordinary world: a planet that’s illuminated by four suns. We’ll have more about the search for exoplanets tomorrow. Script by Ken Croswell, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Summer is months away, but the season’s best-known star pattern is already peeking into view in the pre-dawn sky. The Summer Triangle - marked by the stars Vega, Deneb, and Altair - is well up in the east at first light. The Kepler spacecraft has been staring at that region of sky for the last four years. The space telescope is monitoring about 150,000 stars for evidence of planets. And so far, it’s been quite a success. Mission scientists have found more than 2700 possible planets in Kepler’s observations. They’re using ground-based telescopes to confirm the discoveries. And they’re getting help from the general public to find even more planets. Kepler finds a planet by watching it pass in front of its parent star, causing the star’s light to dip by a tiny amount. Computers sift through the thousands of hours of observations to find these dips. But the computers can’t catch everything. So a project known as Planet Hunters is using the human eye and brain to snag what the computers missed. Participants are shown plots of the light from target stars, and they look for the signature of a passing planet. If enough users identify a candidate planet, then scientists will try to confirm it with follow-up observations. The project has already identified several possible planets that the computers missed, and we’ll have more about that tomorrow. In the meantime, you can hunt for planets yourself at the project’s website - planethunters.org. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.

Heartbeats and ringing bells don’t seem to go together. But they’re a perfect match in a set of stars discovered by the Kepler space telescope. The spacecraft hunts for planets orbiting other stars by staring at the same patch of sky non-stop. That steady vision also allows it to see changes in stars. For example, it’s discovered binary systems where the distance between the two stars varies dramatically. When the stars are far apart, they’re round, like normal stars. But when they come close together, their gravitational pull distorts one or both stars, making them much bigger around the middle. That increases the surface area of the stars, so they look brighter. And that’s where the heartbeat comes in. When you plot the brightness of one of those stars, it looks a lot like an EKG, with a long, steady line followed by a large, brief spike. The bell part of the story describes what happens to the stars’ interiors. Researchers say the effect of a close approach is like a mallet striking a bell, causing the star to vibrate. The vibrations bounce around the star’s interior and reverberate on the surface. Follow-up observations with ground-based telescopes should allow astronomers to measure the vibrations - revealing details about the insides of stars that move to their own beat. We’ll have more about Kepler tomorrow - including a way for you to find planets that astronomers have missed. Script by Damond Benningfield, Copyright 2013 For more skywatching tips, astronomy news, and much more, read StarDate magazine.