StarDate

The solar system is pretty settled. The planets appear to be following orbits that have remained stable for billions of years. But in the early days, things might have been a lot more chaotic. According to one model, in fact, the giant planets Jupiter and Saturn might have moved much closer to the Sun before they moved back out again. The planets probably took shape from a disk of gas and dust around the Sun. Small bits of material stuck together to make bigger bits, all the way up to planets. But much of the material remained free. There was enough of it to exert both a drag and a pull on the giant planets. In this model, Jupiter — the Sun’s heaviest planet — was born at about two-thirds of its present distance from the Sun. It quickly moved inward, though, all the way to the orbit of Mars. Saturn — the second-most-massive planet — was dragged inward as well. Jupiter and Saturn thinned out the supply of gas and dust and the leftover planetary building blocks — either by scooping them up or kicking them away from the Sun. That changed the gravitational balance of the solar system. Jupiter and Saturn moved outward — settling into their current stable orbits around the Sun. Saturn is in the dawn sky now, and looks like a bright golden star. Unlike a star, though, it doesn’t twinkle — its light holds steady. Tomorrow, it will stand close to the left of the Moon. The Moon will pass between Saturn and Mars the next morning; more about that tomorrow. Script by Damond Benningfield

One of the larger moons of the planet Neptune has been through a lot. It might have started as an asteroid, and was captured by Neptune’s gravity. Or it might have started as a moon, but was hurled into a wild orbit when Neptune grabbed its largest moon. And since then, it’s been battered by impacts with other space rocks. Nereid was discovered 75 years ago today, by Gerard Kuiper. It was only the second moon seen around the giant planet, and it’s the third-largest of Neptune’s 16 known moons. Kuiper was observing Neptune with the 82-inch telescope at McDonald Observatory. In a pair of 40-minute exposures, the moon showed up as a tiny star near the planet. Kuiper suggested the name Nereid because, in mythology, the Nereids were daughters of Neptune. We don’t know a lot more about the moon today than when it was discovered. It’s more than 200 miles in diameter, its gray surface probably is coated with ice and rock, and the surface is rough — perhaps the result of billions of years of impacts. Nereid follows the most lopsided orbit of any good-sized moon in the solar system. It ranges from less than a million miles from Neptune to about six million miles. That suggests that Nereid could be the last of Neptune’s original moons. When Neptune captured its biggest moon, Triton, Triton’s gravity could have kicked out all the others, leaving only Nereid — in a wild orbit around a giant planet. Script by Damond Benningfield

Earth’s magnetic field sometimes does a flip. The north magnetic pole becomes the south pole, and vice versa. On average, it happens once every few hundred thousand years. But sometimes, it’s more of a flip flop — the field flips right back over. One flip-flop took place about 42,000 years ago. Known as the Laschamps Excursion, the flip lasted only a few hundred years. And a recent study said the transition could have been a major problem for Earth’s environment. The magnetic field protects us from radiation from the Sun and beyond. As the field flips, though, it gets weaker. That allows more radiation to reach the upper atmosphere, where it can zap the ozone layer. In turn, that allows more radiation to reach the surface, where it can cause skin cancers, mutations, and other problems. During the Laschamps era, the magnetic field dropped to only a few percent of its current strength. Scientists studied the effect of that drop by examining trees buried in New Zealand. The trees’ annual growth rings contained high levels of radioactive carbon — an indication that more radiation was reaching the surface. The researchers said that the weaker field could have been related to major climate changes, including animal extinctions in Australia. No other research has reported such dramatic impacts from a flip. So it’s unclear what effect the next flip — or flip-flop — might have on life on our planet. Script by Damond Benningfield

Earth’s magnetic field is a protective blanket. It keeps charged particles from the Sun and beyond from hitting the surface and much of the atmosphere, where they could cause a lot of problems. But it’s a lumpy blanket. It doesn’t provide the same level of protection for the whole planet. Instead, the magnetic field has peaks and valleys. Today, there’s a deep “valley” over parts of South America and the South Atlantic Ocean. Known as the South Atlantic Anomaly, it allows particles in Earth’s radiation belts to come closer to the surface than anywhere else. That’s a big problem for orbiting spacecraft. Some have been damaged when they passed through the anomaly. The International Space Station has extra shielding to keep its crew safe. About 3,000 years ago, there was a big “peak” in the magnetic field over the Middle East. The field was stronger than usual there, and stayed that way for centuries. Some of the most recent evidence for it came from bricks from Mesopotamia, around present-day Iraq. The bricks contain bits of iron oxide. When the bricks were fired, the iron particles recorded the condition of the magnetic field at the time. The bricks also contained the seals of kings. Archaeologists know just when the kings ruled. That allowed scientists to piece together the magnetic history of the region — confirming a big “lump” in Earth’s ancient magnetic field. More about the magnetic field tomorrow. Script by Damond Benningfield

Be careful what you say — a single phrase can define a legacy. Consider Frances Baily. He served four terms as president of the Royal Astronomical Society and compiled some of the most important star catalogs in history. But he’s best known for five little words: “like a string of beads.” Baily was born 250 years ago today, in England. As a young man, he traveled to the wilds of North America, then joined the London Stock Exchange. He was especially good at the mathematical side of things, compiling guides about annuities and life insurance. He made a fortune, then retired in 1825 to spend all of his time on astronomy. Baily had already helped establish the forerunner of the royal society. He used his skills from his days in business to compile star catalogs — work that required a lot of tedious calculations. One of them was the leading publication of its time. In 1836, Baily watched a solar eclipse from Scotland. Just before the Sun vanished, he noticed little points of light around the edge of the Moon. Edmond Halley had seen the same thing more than a century earlier. Halley even explained those points: they’re sunlight shining through gaps between lunar mountains and craters. To his fellow astronomers, Baily described them as “a row of lucid points, like a string of beads.” So today, the points are known as “Baily’s beads” — insuring a bit of immortality for an insurance expert-turned-astronomer. Script by Damond Benningfield

Russian astronomer Friedrich Wilhelm von Struve discovered and catalogued thousands of binary stars — pairs of stars that are gravitationally bound to each other. But a system that he first saw in 1829 was so striking that he gave it a special name: Pulcherrima — “the most beautiful.” It honors the contrasting colors of the two stars. One looks pale orange, while the other looks blue-white or even green. The system is also known by an even older name: Izar, “the girdle,” because it represents the middle of Boötes, the herdsman. Regardless of what you call it, most skywatchers agree with Struve: Seen through a telescope, the pair is quite beautiful. The orange star is a giant. It’s burned through its original hydrogen fuel and is nearing the end of its life. As a result, it’s puffed up to many times the diameter of the Sun. That “puffiness” caused the star’s outer layers to cool, which is why it looks orange. Its companion is much hotter, so it shines almost pure white. It looks blue or green only when it’s compared to the orange star. It’s less massive than the companion, so it has a lot longer to go before it reaches its own “giant” phase. Boötes is in the east as night falls. Look for its brightest star, brilliant yellow-orange Arcturus. Izar is the first noticeable star to the left of Arcturus. To the eye alone, it looks like a single point of light. But a telescope reveals the true nature of this colorful duo. Script by Damond Benningfield

The brightest star in the night sky is getting ready to leave it for a while. Sirius, the Dog Star, is low in the southwest as night falls. Over the next few weeks, it’ll sink deeper into the twilight, then disappear from view. Sirius is almost nine light-years away. And it actually consists of two stars, not one. The one we see is a good bit bigger, brighter, and heavier than the Sun. The other is about the same mass as the Sun, but a whole lot smaller — only as big as Earth. That star is a white dwarf. It’s the crushed core of a star that originally was more massive than its companion. Because of those extra pounds, the star aged more quickly. It puffed up to giant proportions. When it could no longer produce energy in its core, it cast off its outer layers, leaving only the dead core. The white dwarf is so small and faint that it’s visible only through a telescope. The bright star of Sirius eventually will suffer the same fate. And so will the Sun — but not for several billion years. Sirius will return to view — in the morning sky — in August, with the exact date depending on your location. From ancient Egypt, it disappeared for about 70 days. Sirius was important in both religious and secular life. So 70 days became the length of time set aside to prepare a dead king’s body for the afterlife. And the star’s reappearance marked the start of a new year — in a calendar regulated by the Dog Star. Script by Damond Benningfield

Stars are huge — anywhere from about 10 times the diameter of Earth to a hundred thousand times or more. Such a scale is just hard to fathom. One way to envision it is to consider how long it would take you to make one turn around such a giant body. An extreme example is Antares, the bright orange heart of Scorpius. It’s to the lower left of the Moon as they climb into good view tonight, after midnight, and about the same distance to the upper right of the Moon tomorrow night. Antares is a supergiant — one of the biggest stars in the galaxy. It’s also one of the brightest and heaviest. The exact numbers are a bit uncertain. In part, that’s because its outer layers are extremely thin — they just kind of taper off into space. And Antares is blobby instead of perfectly round. But a good estimate says it’s almost 600 million miles in diameter — about 75 thousand times wider than Earth. To get a better picture of that, imagine flying around Antares in a passenger jet at 600 miles per hour. At that speed, you could circle the Moon in about 11 hours, and Earth in about 40. And it would take six months to circumnavigate the Sun. For Antares, though, you’d need to pack a lot of movies on your mobile device. That’s because it would take 350 years to make one full turn around it — a whole bunch of frequent-flier miles for circling around a supergiant star. Script by Damond Benningfield

Over the millennia, stars acquire a lot of names. Some make sense, some don’t. And some of them might have gotten mixed up along the way. An example is the fourth-brightest star of Leo, the lion, which is about 58 light-years away. It represents the lion’s hip. A few centuries ago, it was assigned the name “Delta Leonis” — an indication of its ranking within the constellation. But it also has some older names, including Zosma and Duhr. Zosma comes from ancient Greek. It means “the girdle.” But that may be a mixed-up version of the original word, which meant “hip” or “back” — the star’s correct position in the lion’s anatomy. Duhr comes from ancient Arabic. It’s a shortened version of a phrase that means “the lion’s back.” Regardless of the name, Zosma is a pretty impressive star. It’s more than twice the size and mass of the Sun, and about 15 times brighter. And its surface is thousands of degrees hotter. Studies have shown that Zosma could be up to three-quarters of a billion years old. Stars of its mass burn through their nuclear fuel much faster than stars like the Sun. As a result, they live much shorter lives. Zosma should end its “prime-of-life” phase and head into old age in a few hundred million years. It’ll shine hundreds of times brighter than it does now — giving the lion a brilliant hip. Zosma is high in the sky at nightfall. It’s well to the right of Regulus, the lion’s brightest star. Script by Damond Benningfield

Immanuel Kant is best known for his ideas about philosophy, from ethics to the nature of knowledge. But he also played a role in the development of an idea about how planets are born. And while many of the details were off, his basic idea was sound. Kant was born 300 years ago this week, in the German state of Konigsberg. And during his 80 years, he never left it. He enrolled in the University of Konigsberg at age 16. But his father died, and he was forced to leave the university. He became a tutor for well-to-do families. He was able to return and finish his education in 1755. Kant was interested in just about everything — including science. Soon after completing his degree, he wrote about earthquakes, the weather, and more. One of his early works was “Universal Natural History and Theory of the Heavens.” In it, he described a “nebular” hypothesis for the formation of planets. A scientist in Sweden had conceived the idea a couple of decades earlier. Kant developed it further. He wrote that the Sun and planets were born from a nebula — a giant spinning cloud of gas and particles. Gravity caused the cloud to flatten, forming a disk. Material in the disk stuck together to make larger and larger chunks — eventually forming planets. Today, scientists have worked out more of the details. But the basic idea remains the same — Kant’s hypothesis provides a basic description of how planets are born. Script by Damond Benningfield

Few constellations have as many backstories as Virgo, the virgin. In ancient Greece and Rome, it was linked with several goddesses, each with her own story. In one story, she was Dike, the goddess of justice. She lived when the gods known as the Titans ruled the land. Everything was peaceful, it was always spring, and living was easy. But after Zeus and the Olympians defeated the Titans, life got much more complicated. The goddess had to work a lot harder to maintain peace. Eventually, things got so bad that she turned her back on humanity and settled among the stars. In another story, Virgo was Demeter, the goddess of agriculture and the harvest. The Sun entered that region of the sky in the fall, around the time of the harvest, strengthening the connection. Virgo’s brightest star is Spica — a name that means “an ear of grain.” It’s the only truly bright star around. It’s about 250 light-years away, and consists of two stars in a tight orbit around each other. The more massive of the two is likely to end its life as a supernova — a titanic blast fit for the early gods of ancient Greece. Spica stands just a whisker away from the full Moon tonight. They’re low in the southeast as twilight fades, separated by about half a degree — less than the width of a pencil held at arm’s length. They arc low across the south during the night, and set around dawn. Tomorrow: an early recipe for a system of planets. Script by Damond Benningfield

If you look straight up as the sky gets dark this evening, you won’t see much of anything. The region that’s high overhead is populated by some especially faint stars and constellations. But there’s a ring of brighter stars around it. The point directly overhead is called the zenith. And most of the time, unless you’re lying on a blanket and just watching the stars, you’re not likely to pay it much attention. It’s just too uncomfortable to tilt your head back that much. Instead, most of us look at what’s closer to eye level. Sometimes, it’s worth looking up there. Tonight really isn’t one of those times. The constellations near the zenith at nightfall include Leo Minor, the little lion; Lynx, a constellation so faint that you need the eyes of a cat to see it; and the part of Ursa Major that includes the feet and legs of the great bear, which are faint. And there’s an almost-full Moon in the sky, which overpowers dimmer stars. But if you look a little below the zenith, the view is more impressive. High in the south, for example, there’s Regulus, the bright heart of Leo, the big lion. And about the same height in the west, you’ll find Pollux and Castor, the “twin” stars of Gemini. Finally, in the northeast, you’ll find perhaps the most famous star pattern of all: the Big Dipper. Its stars outline the body and tail of Ursa Major. They’re the easy-to-spot parts of the great bear, standing high in the sky — just not at the zenith. Script by Damond Benningfield

The Little Dipper is famous for the star at the tip of its handle: Polaris, the North Star. Earth’s axis points in that direction, so all the other stars in the night sky appear to circle around it. The second-brightest star in the dipper is Kochab, at the lip of the bowl. It isn’t nearly as famous as Polaris, but it’s almost as bright. Kochab is a giant — more than 40 times the Sun’s diameter, and almost 400 times its brightness. It’s so big because it’s nearing the end of its life. The nuclear reactions deep inside the star push on the surrounding layers of gas, making them puff outward. Just when a star enters the giant phase of life depends on its mass. Heavier stars age much faster, so they “burn out” more quickly. And Kochab is more massive than the Sun. But just how massive has been the subject of debate. Studies using different techniques have yielded estimates of about 1.3 to 2.5 times the Sun’s mass. If Kochab had a companion star, it would be easy for scientists to measure the masses of both stars. For solitary stars like Kochab, though, astronomers rely on models of how stars behave. Today, the models seem to indicate a mass of about 2.2 times the Sun’s. But that isn’t completely settled. Until it is, we won’t know the complete story of Kochab. Kochab is moderately bright, and stands to the right of Polaris at nightfall. It rotates directly above the Pole Star in the wee hours of the morning. Script by Damond Benningfield

The Lyrid meteor shower is building toward its peak, on Sunday night. The Moon will be almost full then, so its glare will wash out all but the brightest of the “shooting stars.” The shower is the offspring of Comet Thatcher 1861. The comet orbits the Sun once every 415 years or so. As Thatcher approaches the Sun, some of the ice at its surface vaporizes. That releases small bits of dirt and rock into space. This debris spreads out along the comet’s path. Earth flies through this path every April. Some of the comet dust slams into our atmosphere and burns up — forming meteors. At least, most of it does. It’s likely that some of the grains fall to the surface. In fact, a recent study might have found some of those grains at the bottom of New York’s Hudson River. Researchers sifted through layers of sand and mud deposited thousands of years ago. The layers included fossils of microscopic organisms that were coated with tin — an element that likely came from outside Earth. The scientists also found other elements that probably originated outside our planet as well. The layers were laid down at roughly 400-year intervals — suggesting a possible connection with Comet Thatcher and the Lyrid meteors. The findings are preliminary. So we don’t know for sure whether there’s a link between the sediments at the bottom of the Hudson River and the streaks of light in April’s night skies. Script by Damond Benningfield

The Small Magellanic Cloud is a satellite galaxy of the Milky Way. It’s about 200,000 light-years away, it contains hundreds of millions of stars, and it’s easily visible to the eye alone — from the southern hemisphere. And it may actually consist of two separate but related halves — two galaxies for the price of one. Astronomers had suggested that possibility almost four decades ago. And a recent study provided the best evidence yet to support the idea. It found two large star-forming regions that are separated by about 15,000 light-years. One lines up in front of the other, making it hard to see them as individual objects. A team studied the galaxy in several ways. It found that gas and dust are split into two distinct regions. Their material moves in different ways, and has a different composition. The researchers also studied hot, young, bright stars. That also revealed two separate regions. And like the gas, the stars in the regions move in different ways, and have a slightly different makeup. The team said the two regions could be remnants of two galaxies that came together long ago. On the other hand, the region that’s closer to us could be the main body of the galaxy. The region behind it then could be a tail of stars and gas pulled out by the gravity of the nearby Large Magellanic Cloud, which is bigger and heavier. Either way, this close companion to the Milky Way may be more than meets the eye. Script by Damond Benningfield

The heart of the lion stays close to the Moon the next couple of nights. The bright star that marks the lion’s heart is Regulus. It’s to the lower left of the Moon at nightfall this evening, and to the upper right of the Moon tomorrow evening. Regulus is impressive. It’s a system of four stars, but only one shines bright enough to see. Known as Regulus A, it’s almost four times the Sun’s mass, and more than 300 times the Sun’s brightness. But the Moon is even closer to another star of Leo that’s more impressive. Eta Leonis is to the upper left of Regulus. It looks fainter than Regulus. Under the glare of the nearby Moon, in fact, it can be hard to see — especially from light-polluted cities. That’s only because Eta Leonis is much farther than Regulus — about 1800 light-years, versus only 79 light-years for Regulus. In fact, Eta Leonis is a one-percenter — among the biggest and brightest stars in the galaxy. Studies show that it’s about 10 times heavier than the Sun, about 50 times wider, and about 20 thousand times brighter. Eta Leonis is only about 25 million years old, compared to four and a half billion years for the Sun. But thanks to its great mass, the star is near the end of its life. Within a few million years, it’s likely to explode as a supernova. For a while, it will greatly outshine every other star in the galaxy — a brilliant beacon for the lion. Script by Damond Benningfield

Two giants of the solar system huddle close together in the evening twilight the next few days. The viewing window is short, so you need to time it just right to see them. Jupiter and Uranus are low in the west as twilight fades. Jupiter is easy to pick out — it looks like a brilliant star. Uranus is just above it tonight, by about the width of your finger held at arm’s length. But you need binoculars to pick it out. The planets will slide past each other on Sunday night. Uranus is the Sun’s third-largest planet — four times the diameter of Earth. Its atmosphere is topped by an organic “haze,” which makes it tough to see much below it. The atmosphere consists mainly of hydrogen and helium. These elements are left over from the planet’s formation, from the cloud of gas that enveloped the young Sun. The third-most-abundant member of the atmosphere is methane. It’s found mostly near the top of the atmosphere. Methane absorbs redder wavelengths of light, so Uranus looks like an almost featureless blue-green ball. Methane is at least partially responsible for the high-altitude haze. Methane itself makes up part of the haze. The ultraviolet light from the Sun breaks apart some of the methane molecules. Their carbon and hydrogen then combine in different ways to make ethane, acetylene, and other compounds. So the haze is like the smog found over major cities — blocking much of this giant planet from view. Script by Damond Benningfield

The star Arcturus is a little bit heavier than our own star, the Sun. Yet that small difference has a big effect on the star’s evolution: Arcturus entered a late stage billions of years earlier than the Sun will. Arcturus is one of the brighter stars in the night sky, and shines yellow-orange. Both of those traits are a result of its stage in life, which was triggered by its mass. Mass is the key to how quickly a star consumes the hydrogen in its core. The gravity of a heavier star squeezes its core more tightly, making it hotter. That revs up the star’s nuclear engine, causing it to “burn” through the hydrogen faster than a less massive star. When the hydrogen is gone, the core shrinks and gets even hotter. The star’s outer layers then expand and cool, making its surface look redder. In technical terms, the star becomes a red giant. And that’s what’s happened with Arcturus. So even though it’s only about eight percent more massive than the Sun, it’s 25 times wider and a couple of hundred times brighter. And its surface is cooler, so it looks redder than the Sun. Arcturus is about seven billion years old. That’s older than the Sun, but not as old as the Sun will be when it becomes a giant: It won’t reach that stage of life until it’s more than 10 billion years old. Look for Arcturus in the east at nightfall, and soaring high overhead during the night — a puffy star that’s nearing the end of its life. Script by Damond Benningfield

The Moon creeps up on the twin stars of Gemini this evening. As night falls, Pollux and Castor are above the Moon. Pollux is on the left, and is a bit brighter than its “twin.” There’s a lot more to Gemini than just the twins — or even the other stars that are visible to the unaided eye. In fact, one of its most intriguing objects produces most of its energy in the form of X-rays and gamma rays, which are far beyond the range of the human eye. The object is known as Geminga — short for “Gemini gamma-ray source.” It was discovered in the 1970s, but it took decades for astronomers to figure it out. Geminga is a neutron star — the dead core of a star that exploded as a supernova more than 300,000 years ago. It’s more massive than the Sun, but only about a dozen miles in diameter. That means it’s compressed to billions of times the density of ordinary matter. Geminga rotates four times per second. As it spins, it sends out beams of energy — mostly gamma rays, the most powerful form of energy. The dead star is racing through the galaxy at about 270,000 miles per hour. As it rams into gas in its path, material in a disk around the star is ripped away, forming a tail. At the same time, jets of particles that beam out from its poles form a double tail about half a light-year long. So Geminga is like a fast, heavy ship plowing through the interstellar sea, leaving a long, bright wake in its path. Script by Damond Benningfield

This time of year is pretty inviting for some evening skywatching. The evening hours are warm but not usually too hot, and spring storm activity generally hasn’t reached its peak — pleasant conditions for watching the stars. Unfortunately, one of the most beautiful star patterns is dropping from view, so there aren’t many more weeks to enjoy it. Orion the hunter is low in the west as night falls. Its three-star belt stands almost parallel to the horizon. And its two brightest stars bracket the belt: orange Betelgeuse above, and blue-white Rigel below. Orion climbs into prominence in the evening sky around Thanksgiving and Christmas. At that time of year, it’s in view for most of the night. As the months roll by, though, so does Orion. The constellation rises earlier each night, so by late February, it’s halfway across the southern sky at nightfall. And now, it’s about to drop from view. There’s only an hour or two of really good viewing time — between the end of twilight and the time Orion’s stars begin to set. And that viewing window gets shorter by the night. By mid-May, it’ll be hard to see the constellation at all. Fortunately, though, there’s still a lot to look at after Orion passes from view. And the hunter won’t stay gone forever. He’ll begin to climb into the morning sky in August, and return to the evening sky during the longer, colder nights at year’s end. Script by Damond Benningfield