StarDate

As most parents can tell you, coming up with names isn’t easy. It sometimes takes a while to settle on something that sounds just right. It wasn’t easy for the people who named the constellations, either. Some of the names sound like they just gave up. They picked a region of the sky with few stars, gave it the name of a nearby bright constellation, then added the word “minor.” All three of these minor constellations are in good view at dawn: Ursa Minor, Canis Minor, and Leo Minor. The most famous of the bunch is Ursa Minor – the little bear. Seven of its stars form the Little Dipper, which is in the north – directly below the Big Dipper, which is part of Ursa Major. The constellation is especially well known because its brightest star is Polaris, the Pole Star. It’s at the tip of the little bear’s tail. Canis Minor is the little dog. It’s about half way up the sky in the west-southwest. It has only a couple of bright stars. The brightest is Procyon – a name that means “before the dog.” That’s because the little dog leads the big dog across the sky. In ancient Greece, in fact, the constellation was known as Procyon. Finally, Leo Minor is high overhead. It’s the little lion, standing on the shoulder of Leo. That region of the sky wasn’t depicted as a separate constellation until 1687. Today, though, it’s one of the 88 official constellations – even if it is a “minor” one. Script by Damond Benningfield

The shortest season on the planet Mars begins today – autumn in the northern hemisphere, and spring in the southern hemisphere. It will last for 142 Mars days – almost eight weeks less than the longest season. Mars has seasons for the same reason that Earth does – it’s tilted on its axis. And the tilt is at almost the same angle as Earth’s. But the seasons on Mars are more exaggerated because the planet’s orbit is more lopsided. A planet moves fastest when it’s closest to the Sun, and slowest when it’s farthest from the Sun. That stretches out some seasons, and compresses others. It also changes the intensity of the seasons. Mars is farthest from the Sun when it’s summer in the northern hemisphere. So northern summers are fairly mild, while southern winters are bitterly cold. On the flip side of that, northern winters are less severe, while southern summers are the warmest time on the whole planet. The start of northern autumn also marks the beginning of dust-storm season. Rising currents of air can carry along grains of dust. Enough dust can be carried aloft to form storms that cover thousands of square miles. And every few Martian years, a storm gets big enough to cover the entire planet. The storms usually peak around the start of southern summer. Mars is about to pass behind the Sun, so it’s hidden in the Sun’s glare. It’ll return to view, in the dawn sky, in early spring – on Earth. Script by Damond Benningfield

The Moon slides by Saturn the next couple of nights. The planet looks like a bright star. It’s to the left of the Moon as night falls this evening, and to the lower right of the Moon tomorrow night. Saturn is best known for its rings. They’re almost wide enough to span the distance from Earth to the Moon. Right now, we’re viewing them almost edge-on, so they look like a thin line across the planet’s disk. Saturn isn’t the only world with rings. The solar system’s three other giant outer planets also have them. But they’re dark and thin, so they’re hard to see. Several asteroids and dwarf planets have rings, too. But the biggest set of rings yet seen may encircle a “rogue” planet about 450 light-years away. The possible rings were discovered years ago. Over a period of eight weeks, the light of a star in Centaurus flickered – sometimes dropping to just five percent of its normal level. The most likely cause was the passage of a set of rings in front of the star. And it’s quite a set. The rings are more than a hundred million miles across – greater than the distance from Earth to the Sun. The ringed planet appears to be traveling through the galaxy alone, and it just happened to pass in front of the star. It could be up to six times the mass of Jupiter, the giant of our own solar system. And moons could be orbiting inside the rings – the most impressive rings we’ve seen anywhere in the galaxy. Script by Damond Benningfield

Planets are tough little buggers. They can form and survive in some extreme environments. In fact, the first confirmed planets outside our own solar system orbit the remnant of a dead star – a pulsar. A pulsar is tiny – the size of a small city. But it’s more massive than the Sun. A teaspoon of its matter would weigh as much as a mountain. Yet a pulsar spins rapidly – up to several hundred times per second. It has an extreme magnetic field. The field shoots “jets” of particles out into space. As the pulsar spins, the jets can sweep across Earth like a lighthouse beacon, producing short pulses of energy. The timing of those pulses is extremely precise. That makes pulsars some of the best clocks in the universe. But the timing can be changed by a companion – another star, or even a planet. And that’s how pulsar planets are discovered – through tiny changes in the timing of the pulses. Eight pulsar planets have been confirmed. But they present quite a challenge. A pulsar is the remnant of a titanic explosion – a supernova. It’s hard to see how any planets could survive such a blast. So it’s likely that the planets formed after the blast – perhaps from debris from the explosion’s aftermath. Regardless of how they formed, the planets aren’t friendly places. They’re blasted with charged particles, X-rays, and gamma rays from the pulsar. That may slowly erode the planets – no matter how tough they are. Script by Damond Benningfield

[pulsar audio] This is the rhythm of the stars – the beat of dead stars. It’s the “pulses” of radio waves produced by rapidly spinning stellar corpses. They produce beams of energy that sweep around like the beacon of a lighthouse. Radio telescopes detect the beams when they sweep across Earth. The stars are known as pulsars. They’re some of the most extreme objects in the universe. They’re neutron stars – the dead cores of some of the most massive stars. When a heavy star can no longer produce nuclear reactions in its core, the core collapses. Gravity squeezes the core down to the size of a small city. But that tiny ball is heavier than the Sun. The star is rotating as it dies. As the core collapses, it keeps on spinning. But the smaller it gets, the faster it spins. So newborn neutron stars can spin a few dozen to a few hundred times per second. Particles trapped in the neutron star’s magnetic field produce energy that’s beamed into space – the source of the pulses. The neutron star spins down over time, slowing the pulses. But if it has a close companion, it can be revved up even faster. The neutron star can pull gas from the surface of the companion. As it hits the neutron star, the gas acts like an accelerator – creating some of the fastest pulsars in the universe. These extreme stars can still host planets; more about that tomorrow. Script by Damond Benningfield

Getting too close to a black hole is bad news. The black hole’s gravity can pull apart anything that’s falling into it atom by atom. A magnetar can do the same thing. And it’s not just its gravity you have to worry about. Its magnetic field can do the job as well – from hundreds of miles away. A magnetar is a neutron star -the crushed corpse of a once mighty star. It’s heavier than the Sun, but only a little bigger than Washington, D.C. It’s born when a massive star can no longer produce nuclear reactions in its core. The core collapses, while the star’s outer layers explode. The original star generated a strong magnetic field. As the core collapsed, the field was mashed inward as well, making it extremely powerful. It’s boosted by the turbulent sloshing inside the newly formed neutron star. So a typical magnetar’s magnetic field is a million billion times the strength of Earth’s field. The neutron star sticks around, but its magnetic field weakens in a hurry. So there aren’t many magnetars around – only about 30 have been discovered. The magnetic field can help produce titanic explosions. Interactions with the field can cause the crust of a neutron star to crack in a “starquake.” Energy from the quake is beamed out by the magnetic field, producing an outburst of gamma rays. The most powerful quake yet seen generated more energy in a tenth of a second than the Sun will emit in 150,000 years – the enormous power of a magnetar. More about neutron stars tomorrow. Script by Damond Benningfield

When the most massive stars die, they can leave behind two types of corpse. The heaviest ones probably form black holes. But the fate of the others is no less exotic. They form neutron stars – ultra-dense balls that are more massive than the Sun, but no bigger than a small city. A massive star “dies” when its core can no longer produce nuclear reactions. For a star of about eight to 20 or more times the mass of the Sun, the core collapses, while the star’s outer layers explode as a supernova. The gravity of the collapsing core squishes together protons and electrons to make neutrons – particles with no electric charge. The neutrons can be squished together only so much before they halt the collapse. By then, the core is trillions of times as dense as Earth. So a chunk of a neutron star the size of a sugar cube would weigh as much as a mountain. A neutron star probably has a solid crust made of iron or other elements, with no features more than a couple of millimeters tall. The gravity at the center of a neutron star is so strong that we don’t really know what the conditions are like – there’s just nothing to compare it to. There could be as many as a billion neutron stars in the galaxy. But they’re hard to find. Some of them make it a little easier, though. They produce the most powerful magnetic fields in the universe – and some of the most powerful outbursts. More about that tomorrow. Script by Damond Benningfield

You can always count on the constellations. Over the course of a human lifetime, their configuration doesn’t change – they don’t appear to move at all. That’s an illusion, though. The stars are all so far away that we don’t see any motion. But they’re all moving in a hurry. And one of the fastest is in view on autumn evenings. Gamma Piscium is the second-brightest member of Pisces, the fishes. The constellation stretches across the east and southeast at nightfall. Gamma Piscium is near its top right corner – part of a pentagon of faint stars. Gamma Piscium is a giant. It’s nearing the end of its life, so it’s getting bigger and brighter. Right now, it’s about 10 times the diameter of the Sun, and more than 60 times the Sun’s brightness. That makes it faintly visible to the eye alone, even though it’s 135 light-years away. Perhaps the most interesting fact about Gamma Piscium is its speed: It’s moving through the galaxy at about 340,000 miles per hour – faster than all but a few other visible stars. At that rate, it’ll move the equivalent of the Moon’s diameter in less than 3,000 years. The star’s composition hints that it came from outside the disk of the Milky Way – the part of the galaxy that includes the Sun. The star has very few heavy elements. That suggests it formed outside the disk, and just happens to be passing by – zipping through the galaxy like a speeding rocket. Script by Damond Benningfield

An interloper from another galaxy scoots low across the south on October evenings. It’s a tight family of stars – hundreds of thousands of them. The stars probably belonged to another galaxy that was consumed by the Milky Way in the distant past. Messier 30 is low in the south at nightfall, in Capricornus. The sea-goat’s brightest stars form a wide triangle. M30 is on the lower left side of the triangle Messier 30 is a globular cluster – a ball of stars about 90 light-years wide. Most of the stars are concentrated in the cluster’s dense core. The numbers tail off as you move toward the cluster’s edge. Anything that wanders too far from the center gets yanked away by the gravity of the rest of the galaxy. The Milky Way is home to more than 150 globular clusters. But several of them appear to have come from other galaxies. And that includes M30. The main clue to its origin is its orbit. As it circles the center of the galaxy, M30 moves in the opposite direction from most of the stars and star clusters. The only way for such a massive cluster to move against the traffic is if it came from outside the galaxy. So Messier 30 isn’t a native of the Milky Way. Instead, it was pulled in by the Milky Way’s powerful gravity – making it a refugee from another galaxy. We’ll talk about an individual star that might be a refugee from another part of the galaxy tomorrow. Script by Damond Benningfield

If you’ve ever left a can of soda in the freezer for too long, you can appreciate what happened to the largest moon of the planet Uranus: It cracked. Titania is almost a thousand miles in diameter – less than half the size of our moon. But it orbits Uranus at about the same distance as the Moon does from Earth. And like the Moon, it’s locked in such a way that the same hemisphere always faces its planet. When Titania was born, its interior was warm. But it quickly froze. As it did so, the surface cracked, creating some impressive canyons. The largest is a network known as Messina Chasma. Like Titania itself, it’s named for a character from Shakespeare – in this case, from “A Midsummer Night’s Dream`.” The canyons are more than 900 miles long, wrapping from the equator to near the south pole. They’re up to 60 miles wide, and miles deep. Few impact craters have scarred Messina, indicating that it’s fairly young. In fact, Titania’s entire surface appears to be younger than those of Uranus’s other big moons. That doesn’t mean the moon itself is younger. Instead, it probably was repaved by ice flowing from inside – resetting the clock for this fractured moon. Uranus is in view all night, in Taurus. And it’s closest to Earth for the year – 1.7 billion miles away. Despite the distance, it’s big enough that it’s an easy target for binoculars. But you need a decent telescope to see Titania. Script by Damond Benningfield

The planet Uranus has always been an oddball. It lies on its side, so it rolls around the Sun like a giant bowling ball. Its magnetic field is tilted and offset more than any other planet’s. And for the past four decades, it’s seemed that the planet radiated less energy into space than it receives from the Sun. The solar system’s other giant planets all radiate at least twice as much energy as they receive – mainly in the form of heat left over from their formation. But two recent studies have changed that story – at least a little. Most of the earlier estimates were based on observations by Voyager 2, which flew past the planet in 1986. But the new studies found that Voyager might have scanned Uranus at the wrong time. The Sun was especially active then, skewing the readings. The studies combined decades of observations by telescopes on the ground and in space. Researchers then used computer models to analyze the results. They found that Uranus emits up to 15 percent more energy than it gets from the Sun. But that’s still a lot less than the other giants. So Uranus is still an oddball – just not quite as odd as it seemed. Uranus is at its best this week. It’s opposite the Sun, so it’s in view all night. It’s closest to us for the year as well, so it shines at its brightest. Even so, you need binoculars to see it. It’s in the east in early evening, to the lower right of the Pleiades star cluster. Script by Damond Benningfield

If you suffer from seasonal affective disorder during the dark winter months, then stay away from the poles of Uranus. The giant planet is tilted on its side. So during each 84-year-long orbit around the Sun, the polar regions have 42 years of daylight followed by 42 years of darkness – a looong time to feel sad. Planetary scientists have been watching the slow change of seasons for two decades with Hubble Space Telescope. At visible wavelengths, Uranus looks like an almost-featureless ball – faint bands of clouds are about the only details. A smattering of methane in the atmosphere absorbs red light, giving the planet a pale green color. But Hubble’s instruments split the light into its individual wavelengths. It also can see into the infrared, which isn’t visible to the eye. That reveals more details, providing a better picture of what’s going on. Among other things, it’s revealed that there’s not much methane at the poles, regardless of the season. On the other hand, as the north pole warmed up during spring, it got hazier. At the same time, the haze thinned out over the south pole. Scientists are studying those results to learn more about the planet’s atmosphere and the slow march of its seasons. Uranus is low in the east in early evening, to the lower right of the Pleiades star cluster. Through binoculars, it looks like a star with just a hint of color. More about Uranus tomorrow. Script by Damond Benningfield

Uranus is the seventh planet of the solar system, so it’s a long way from both the Sun and Earth. Right now, it’s about 1.7 billion miles away. At that distance, under especially dark skies it’s barely bright enough to see with the eye alone. It’s easy to pick out with binoculars, though. This is an especially good week to look for the planet because it reaches opposition, when it lines up opposite the Sun. It rises around sunset and is in view all night. And it shines brightest for the entire year. In early evening, it’s close to the lower right of another good binocular target, the Pleiades star cluster. Even though Uranus is sometimes visible to the eye alone, it’s so faint that no one realized it was planet for a long time. Every astronomer who saw Uranus logged it as a star, missing out on a chance at immortality. It was officially discovered as a planet by British astronomer William Herschel, in 1781. But even he was fooled by it for a while. When he first saw it, he thought it was a comet. But calculations of its orbit showed that the object was much too far away to be a comet – it had to be a planet, and a big one. Herschel wanted to call it George’s Star after his patron, King George III. Astronomers outside Britain weren’t crazy about that. So almost 70 years later, they finally named it for a Greek god of the sky: Uranus. More about Uranus tomorrow. Script by Damond Benningfield

A barely-there crescent Moon teams up with the disappearing “morning star” in tomorrow’s dawn twilight. But there’s not much time to look for them. The Moon will cross between Earth and the Sun in a couple of days. It’ll be lost in the Sun’s glare. It will return to view, in the evening sky, by Friday or Saturday. Venus is getting ready to disappear in the dawn twilight as well. It will cross behind the Sun on January 6th. It’s a slower passage, so the planet will be hidden in the Sun’s glare for about three months. It’ll emerge as the “evening star” in February. Most cultures figured out that the morning and evening star were actually the same object thousands of years ago. Even so, they had different names for the morning and evening appearances. In ancient Greece, morning Venus was named for the god Phosphorus. In Rome, he was Lucifer. Both names mean “bringer of light” – the god lit the dawn sky with a torch. Venus passes behind the Sun every 584 days – a bit more than 19 months. Before and after it disappears, it’s almost full. So if you look at Venus with a telescope now, it’ll be almost fully lit up – like a negative image of the “fingernail” crescent Moon. Look for Venus and the Moon quite low in the eastern sky beginning about 45 minutes before sunrise. Because of the timing and the viewing angle, they’ll be a little easier to spot from the southeastern corner of the country. Script by Damond Benningfield

If you ever warp over to another star, it would help to know its distance. Say, for example, you wanted to visit Spica, the brightest star of Virgo, which is quite close to the Moon at dawn tomorrow. The system is worth visiting because it consists of two giant stars. They’re so close together that their shapes are distorted, so they look like eggs. The best measurement we have says that Spica is 250 light-years away. But there’s a margin of error of about `four percent. So you could undershoot or overshoot the system by 10 light-years. The distances of most stars are measured with a technique called parallax. Astronomers plot a star’s position at six-month intervals, when Earth is on opposite sides of the Sun. That can produce a tiny shift in the star’s position against the background of more-distant objects. The bigger the shift, the closer the star. But the stars are so far away that the shift is tiny – like the size of a dime seen from miles away – or hundreds of miles. And Earth’s atmosphere blurs the view, so the stars look like fuzzy blobs instead of sharp points. So the most accurate measurements have been made from space. Spica’s distance was measured by Hipparchos, a European space telescope. An even more accurate satellite, Gaia, measured the distances to more than a billion stars – but not Spica. The star was too bright for its detectors – leaving a big margin of error for this impressive system. Script by Damond Benningfield

The patchiest of all meteor showers will be at its best tomorrow night. Unfortunately, this is one of its off years. At best, it might produce a dozen or so “shooting stars” per hour. Over the past two centuries, though, the Leonids have produced some amazing outbursts. The first of these came in 1833. Skywatchers in parts of America reported rates of a hundred thousand meteors per hour – not a shower, but a storm. The nature of meteor showers was unknown at the time, so many saw the outburst as the end of the world. The Leonids flare to life when Earth crosses the path of Comet Tempel-Tuttle. The comet passes close to the Sun every 33 years or so. It sheds tons of material on each pass – tiny bits of rock and dirt. Each cloud of debris spreads out and forms its own stream. A shower takes place when Earth flies through one of the streams. Newer streams are denser, so they produce more intense displays. Those streams congregate near the comet, so the outbursts occur when the comet is close to the Sun. The last outburst came in the early 2000s. And Earth probably won’t pass through another storm-producing stream until the end of the century – leaving us with meager displays of the Leonids. To see this year’s display, find a safe viewing site away from city lights. The meteors can appear anywhere in the sky, so you don’t need to look in a particular direction to see them. The best view comes between midnight and dawn. Script by Damond Benningfield

Galaxies frequently collide with each other, and the results can be spectacular. The encounters can pull out giant ribbons of stars. They can trigger intense bouts of starbirth. And they can scramble a galaxy’s stars and gas clouds, creating beautiful rings that look like cosmic bulls-eyes. One well-known galaxy that’s experienced a head-on collision is the Cartwheel. It’s about 500 million light-years away, in the constellation Sculptor, which is low in the south on November evenings. The Cartwheel is a good bit bigger than the Milky Way. It has a bright inner ring of mainly older stars that’s offset a little from the galaxy’s middle. A brighter ring of younger, bluer stars is far outside it. Wispy spiral arms that look like the spokes of a wagon wheel connect the rings, giving the “Cartwheel” its name. The Cartwheel probably started as a normal spiral galaxy. But a few hundred million years ago, a smaller galaxy plunged through it. The collision created a wave that rippled outward, like a rock thrown into a still pond. The wave disrupted the original spiral structure. It also squeezed clouds of gas and dust, causing them to give birth to new stars. And the drama isn’t over. Many more stars are being born in the outer ring, in giant nurseries that look like a strand of lights on a Christmas wreath. They will continue to make the Cartwheel shine brightly as it spins through the universe. Script by Damond Benningfield

Nicolas-Louis de Lacaille had a great imagination. In the 1750s, the French astronomer mapped more than 10,000 stars from the southern tip of Africa. Lacaille used those stars to create 14 new constellations. One of them is Sculptor. Lacaille originally called it the Sculptor’s Studio. It depicted a carved head atop a stool, plus a hammer and chisel and a block of granite. But all of that takes a lot of imagination to see. All of the constellation’s stars are so faint that Sculptor is invisible from light-polluted cities and suburbs. Sculptor is important to astronomers, though, because many galaxies lie within its borders. The closest of them is the Sculptor Dwarf. It’s just 300,000 light-years away, and it orbits our home galaxy, the Milky Way. The galaxy contains only 30 million stars or so. But most of them are ancient – far older than most of the stars in the Milky Way. That means the Sculptor Dwarf may be a remnant from the early universe – like the many building blocks that came together to form the Milky Way. So studying the galaxy can tell us much more about the early universe, and the history of our own galaxy. From most of the United States, Sculptor is low in the southeast in early evening,. But you need a dark sky to make out any of its stars – and a good imagination to “see” a pattern in them. We’ll have more about Sculptor tomorrow. Script by Damond Benningfield

The brightness of any star that’s in the prime phase of life is controlled by the star’s mass: Heavy stars are brighter than lightweight stars. But it’s not a simple one-to-one kind of relationship. A star that’s twice the mass of the Sun isn’t twice as bright – it’s more than 15 times as bright. That’s because gravity squeezes the core of a heavier star more tightly. That increases the core’s temperature, which revs up the rate of nuclear reactions. That produces more energy, which makes its way to the surface and shines out into space. Regulus illustrates the point. The heart of the lion consists of four stars, three of which are in the prime of life. The star we see as Regulus – Regulus A – is a little more than four times the mass of the Sun, yet it radiates about 340 times more energy. Much of that energy is in the ultraviolet, which we can’t see. But even at visible wavelengths, it’s about 150 times the Sun’s brightness. Regulus A has a couple of distant companions. Regulus B is about 80 percent the mass of the Sun, but only a third of the Sun’s total brightness. And Regulus C is even more dramatic: a third of the Sun’s mass, but just two percent its brightness – a cool, faint ember in the heart of the lion. Look for Regulus standing close above the Moon as they climb into good view around 1:30 or 2 in the morning. The star will be a little farther from the Moon at dawn. Script by Damond Benningfield

Edwin Hubble gets the credit for discovering that the universe is expanding. But that finding was made possible by work done by Vesto Slipher. He was the first to measure the motions of distant galaxies – the key to Hubble’s discovery. Slipher was born 150 years ago today, in Mulberry, Indiana. He worked on the family farm, and developed an interest in astronomy. A college professor helped him get a job as an assistant at Lowell Observatory in Arizona, where he worked for the next five decades. Slipher studied what were called “spiral nebulae.” It wasn’t certain whether these pinwheels were motes of matter in the Milky Way, or “island universes” of stars outside the Milky Way. Slipher used a technique that splits an object’s light into its individual wavelengths. The object’s motion shifts those wavelengths. Objects that are moving away from us are shifted to longer, redder wavelengths. Slipher found that most of the spirals were moving away from us in a hurry. He suggested the objects were far outside the Milky Way. But he couldn’t prove it because he had no way to measure the distances. Hubble did measure the distances, proving that the spirals are separate galaxies. He then combined Slipher’s observations with his own to show that the farther a galaxy, the faster it was moving. Later, astronomers concluded that the universe is expanding – a finding made possible in large part by Vesto Slipher. Script by Damond Benningfield