StarDate

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

Planetary systems can be violent. In our own solar system, for example, the Moon probably was born from the debris left over when a planet as big as Mars rammed into Earth billions of years ago. And the giant planet Uranus probably was knocked over on its side by a similar collision about the same time. A more recent example comes from ASASSN-21qj — a star system that’s about 1800 light-years away, in the constellation Puppis. In December of 2021, astronomers noticed that a Sun-like star there suddenly got a lot fainter. They kept an eye on the system, and also looked through records of its appearance in the past. They found that about two and a half years before it faded, the system grew a lot brighter, especially at infrared wavelengths. A team recently reported a possible cause for all the changes: a massive collision between two planets. Both worlds probably were several times the mass of Earth. The impact made the system look brighter. And it produced a super-heated cloud of debris — gas, dust, and big boulders. This cloud then passed in front of the star, making the system look fainter. In time, much of this debris could come together — making a new giant planet. ASASSN-21qj is quite low in the south as night falls. It’s too faint to see with the eye alone. But it’s close to the brightest star of Puppis, so at least you can spot the location of this violent star system. Script by Damond Benningfield

Planets like Earth live in the “Goldilocks zone” — the region around a star where conditions are most comfortable for life. But most planets aren’t so cushy. They’re either far away and cold, or close in and hot. And some are so close that they’re being vaporized by their star. One example is WASP-69 b. It orbits a cool, faint star about 160 light-years from Earth. The system is in the constellation Aquarius, which is in the southeastern sky at dawn tomorrow. WASP-69 b is only a few million miles from its parent star. At that close range, its atmosphere is heated to more than a thousand degrees Fahrenheit. The heat has caused the planet to puff up. While it’s only about a quarter as massive as Jupiter, the giant of our own solar system, it’s actually a little bigger than Jupiter. That makes it easy for the star to blow away material from the planet’s atmosphere. That gives WASP-69 b a long “tail” like that of a comet. Recent observations found the tail is at least 350,000 miles long — greater than the distance from Earth to the Moon. Even so, the rate at which the planet is vaporizing is pretty slow. It’s losing enough mass to make a planet as heavy as Earth every billion years or so. Considering that WASP-69 b is about 90 times the mass of Earth, this big, hot planet won’t disappear anytime soon. We’ll have more about exoplanets tomorrow. Script by Damond Benningfield

If you heat up some alphabet soup, you shouldn’t end up with all the letters clumped together — they should be fairly evenly spread throughout the pot. According to the current understanding of the universe, the same thing should apply to galaxies. They may clump together on smaller scales, forming clusters and even super-clusters. But when you look at the universe as a whole, the galaxies ought to be evenly spread. Yet astronomers have found giant galaxy structures that seem to defy that idea — they can span billions of light-years. Two recently discovered examples are the Big Ring and the Giant Arc. Both of them appear near the Big Dipper. And they may be related. Both were discovered by a graduate student in England, who used a lot of computing power to produce 3D maps of galaxies. The Giant Arc was discovered first. It spans 3.3 billion light-years. The Big Ring was announced earlier this year. It is about 1.3 billion light-years across. The galaxies in both structures are all about 9.2 billion light-years away. That means we’re seeing them when the universe was just one-third its current age. And the Giant Arc wraps around the Big Ring. The combination suggests the two are related. So far, there’s no real explanation for these giant structures — nothing seems to fit all the observations. So scientists will keep on looking — trying to explain why the letters are clumping together in the cosmic alphabet soup. Script by Damond Benningfield

Europa is one of the more intriguing bodies in the solar system — and one that scientists are especially eager to land a spacecraft on. The big moon of Jupiter may have a global ocean below its icy crust — an ocean that could host life. But landing on Europa won’t be easy. It’s hundreds of millions of miles away, and it’s embedded in Jupiter’s powerful radiation belts. And the surface near its equator could be mottled by fields of icy spikes that are up to five stories high. Such structures are known as penitentes, because they resemble penitent worshippers, on their knees. On Earth, they’re found in high, dry mountains. They’re carved as the Sun evaporates some of the ice, but not all. A study a few years ago suggested that rough terrain near the equator of Europa could consist of similar fields. The spikes would be bigger than those on Earth — up to 50 feet high, and only about 25 feet apart. Other studies disagree with that suggestion. We may find out for sure early in the next decade, when a mission to study Europa reaches the Jovian system. Jupiter stands to the upper left of the crescent Moon early this evening. It looks like a brilliant star. Through binoculars, Europa and some of Jupiter’s other big moons look like tiny stars near the planet. And if you aim your binoculars a little above Jupiter, you can also spot the giant planet Uranus. The Moon will huddle closer to both planets tomorrow night. Script by Damond Benningfield

In case you haven’t heard, there’s a big event this afternoon — a total eclipse of the Sun. Totality is visible along a narrow path from Texas to Maine. The parts of the country outside that path will see a partial eclipse. If you miss it — well, let’s just say it’ll be a long wait until the next great eclipse over the United States. The next total eclipse visible anywhere will take place on August 12th, 2026. Its path will cross parts of Europe, but most of it will cross the high Arctic. The next total eclipse visible from anywhere in the United States is on March 30th of 2033, across Alaska. An eclipse in 2044 will catch Montana and North Dakota, but much of its path will be across Canada. The next great eclipse in the U.S. is on August 12th, 2045. Its path will stretch from northern California, across the Rockies, the southern Plains, and the southeast, all the way to southern Florida. And it really will be a great one — totality will last up to six minutes. Today’s eclipse belongs to a centuries-long series known as Saros 139. The next eclipse in that series is in 2042, mostly over the western Pacific Ocean. So enjoy today’s total eclipse — the last one visible from American soil for a long time. And please remember to watch safely — use eclipse glasses or other approved gear to protect your eyes from the power of the unfiltered Sun. Script by Damond Benningfield

It’s almost time for the year’s big celestial event: a total eclipse of the Sun. Tomorrow afternoon, the Moon will pass directly between Earth and the Sun. That will block the Sun’s disk. The sky will grow dark, with a pink glow around the horizon. Stars and planets will pop into view. And the Sun’s faint outer atmosphere, the corona, will look like silvery ribbons around the Moon. Totality will be visible along a narrow path. In the United States, it’ll stretch from Eagle Pass, Texas, to Houlton, Maine. Several major cities are along that path; the largest is Dallas. At most, totality will last for a bit less than four and a half minutes. Skywatchers in the rest of the contiguous U.S. will see a partial eclipse — the Moon will cover only part of the Sun’s disk. For those lucky enough to find themselves inside the path of totality, it’s perfectly safe to look at the Sun when it’s fully eclipsed. At all other times, though, the Sun is much too bright to look at directly. Even a 99-percent-eclipsed Sun is bright enough to cause eye damage. To see it safely, use proper eclipse glasses, or a piece of welder’s glass — number 14 or darker. If you’re close to a leafy tree, you can follow the eclipse by looking at the ground — the shadows project tiny images of the eclipsed Sun. You can also look at the shadow of a colander or similar device. So enjoy this beautiful alignment — but do it safely! More tomorrow. Script by Damond Benningfield

In the mythology of ancient Egypt, Apep was the serpent god — the rival of Re, the sun god. He chased Re, and sometimes briefly caught him — creating a solar eclipse. NASA plans to launch an experiment named for the serpent god to study the eclipse on Monday. Instruments will fly on three different rockets. They won’t look at the Sun, though. Instead, they’ll study the effect of the eclipse on the ionosphere — a high-altitude layer of Earth’s atmosphere. The ionosphere carries an electric charge. It “bends” radio waves, allowing them to travel far around the planet. During the day, sunlight intensifies the charge. At night, the charge lessens. Scientists want to understand how the ionosphere reacts to the brief loss of sunlight during an eclipse. That should tell them more about the ionosphere overall, and how it changes during the day. Among other ways, they’ll do so by launching Apep. Three small rockets will take flight from a NASA center in Virginia. The rockets will climb about 200 miles high. They’ll deploy several instruments, which will make observations for seven or eight minutes. Then they’ll parachute back to Earth. The same instruments flew during last year’s annular eclipse, when the Moon didn’t fully cover the Sun. This year’s flights will allow scientists to compare the results — learning more about how Earth’s atmosphere reacts when the Sun grows darker. More about the eclipse tomorrow.