We never know everything there is to know about a person from the first glance – or anything else, for that matter. And that includes the stars. It takes a lot of time, and a lot of looks with different instruments, to piece together the whole story. One example is the system Gaia BH2. It consists of two known objects. But there might once have been a third object – a star that was gobbled up. The system was discovered by Gaia, a space telescope. It revealed two objects: a black hole about nine times as massive as the Sun, and a giant star about 1.2 times the Sun’s mass. They orbit each other once every three and a half years. Ground-based telescopes revealed the composition of the giant. Its chemistry looked like that of an ancient star. But observations by TESS, another space telescope, suggested otherwise. The satellite measured “starquakes” on the surface of the giant star. Sound waves bounce around inside the star and back to the surface. So just as an earthquake tells us what’s happening below the surface of Earth, a starquake tells us what’s happening deep inside a star. The quakes revealed that the star spins faster than expected. That suggests it was spun up by interactions with something else. It might have swallowed debris that encircled the black hole. Or it might have swallowed another star, changing the chemistry at its surface – prematurely “aging” this giant star. Script by Damond Benningfield

The stars of Spica may be headed for a breakup. One of the two stars is likely to explode as a supernova. That may send the stars careening into the galaxy on their own. Spica is the brightest star of Virgo. It rises just above the Moon early this evening. The system consists of two big, heavy stars. The primary star, Spica A, is about 10 times the mass of the Sun. Spica B is about seven times the Sun’s mass. The stars are so close together that they whirl around each other once every four days. Within a few million years, Spica A will consume all the nuclear fuel in its core. The core will collapse, probably forming a neutron star – an object up to twice the mass of the Sun, but only as big as a city. Its outer layers then will blast into space at a few percent of the speed of light – a supernova. The companion star should survive, although it might lose some gas from its surface. But what happens next is tricky. Supernovas sometimes explode asymmetrically – the blast can be off-centered. That can give the neutron star a big kick. And the neutron star will be only a fraction as massive as the original star. That means its gravitational grip on its companion will be much weaker. The neutron star could zip off at high speed – perhaps fast enough to escape the galaxy. And even if that doesn’t happen, the stars are likely to move farther apart – a bigger gap between these impressive stars. Script by Damond Benningfield

Mercury is just peeking into view in the dawn sky. The little planet is in the east in the waxing twilight, and looks like a bright star. It’ll stand highest in the sky on Friday. But because of the angle at which it rises, it’s hard to spot. In fact, from much of the United States, you probably can’t see it at all. The view is best from south of about Dallas. That difficulty illustrates how tough it’s been for scientists to study Mercury. It’s never in view for long – no more than a couple of hours before sunrise or after sunset. And it’s so low in the sky that we always see it through a thick layer of air, so the view is murky – like trying to make out the shapes of clouds from the bottom of a swimming pool. In the late 1800s and the early 1900s, astronomers did make a few crude maps of Mercury’s surface. But there was a lot they couldn’t figure out. That included the length of the planet’s day. At first, it appeared that Mercury completed one turn on its axis in 88 Earth days – the same length as its year. In the early 1960s, though, astronomers bounced radio waves off the surface. That work showed that a day lasts 59 Earth days. So Mercury completes three turns on its axis for every two orbits around the Sun – three days for every two years. Again, look quite low in the east not long before sunrise for elusive little Mercury – a planet that’s been hard to get to know. Script by Damond Benningfield

For skywatchers, tonight’s a time for old friends. There’s an almost-full Moon, so its glare overpowers most of the stars in the night sky. But the brighter stars shine through – the most familiar ones. That includes the stars of the Big Dipper, which are in the northeast at nightfall. The dipper’s leading light is Alioth. It’s the first star in the handle. It’s about 80 light-years away. But it’s an easy target because it’s about a hundred times brighter than the Sun. That’s because it’s bigger and hotter than the Sun. Alioth is classified as a “peculiar” star – its chemical makeup is unusual. Astronomers measure its chemistry by breaking the star’s light into its individual wavelengths. Each element in the star imprints its own “barcode” in that pattern of light. But the mixture of elements in Alioth is different from most stars. Some elements are especially common, while others are unusually rare. And the mixture changes as the star turns on its axis. That behavior is caused by the star’s odd magnetic field. It’s tilted so far that the magnetic poles lie roughly along the star’s equator. Thanks to that alignment, the magnetic field pulls some elements to the surface, and concentrates them in specific locations. It pushes other elements down, so we can’t see them. So Alioth is both familiar and peculiar – an old friend that’s easy to pick out through the glare of the full Moon. Script by Damond Benningfield

Astronomers have been trying to hear from other civilizations for two-thirds of a century. So far, not a peep. But finding E-T might be the easy part. Actually having a conversation might be a lot harder. We wouldn’t know what the other folks were saying – or whether they were interested in talking at all. To gain some insight, scientists have been studying some “non-terrestrial” intelligences here on Earth – whales and dolphins – species that live in the oceans instead of on land. Many of them have complex communications with each other. And some of them interact with humans. One example is humpback whales. They’re playful and curious, and they often approach boats and divers. And a recent study suggested that they might be trying to have a conversation. Researchers found a dozen times when humpbacks blew special bubbles while they were near people. The bubbles looked like smoke rings, a few feet across. The bubbles were different from those associated with other behavior, such as courting or “corraling” fish. In most cases, a whale first approached the people, then moved away a bit and blew one or more rings. Some of the whales poked their heads up through the rings. The researchers said the whales might have been trying to play, or to see how the people responded. But the bubbles could have been an attempt to communicate – starting a conversation between terrestrial and non-terrestrial life. Script by Damond Benningfield

The star Regulus leads the Moon across the sky tonight. The bright heart of the lion is close to the upper right of the Moon at nightfall, with the gap increasing as the hours roll by. Regulus is about 79 light-years away. That means the light you see from Regulus tonight actually left the star about 79 years ago. So when a particle of light from Regulus hits your eye, it’s ending a journey of 79 years. As with many things astronomical, though, it’s all relative. For the particle of light itself – a photon – the trip took literally no time at all. That’s because the photon was traveling at the speed of light – 670 million miles per hour. Nothing can travel faster than that. And only photons can travel at that speed. That’s because photons have no mass – they weigh nothing at all. If anything else were to travel at lightspeed, it would become infinitely massive. So physical objects are limited to just below lightspeed. As an object moves faster, time appears to slow down for it as viewed by an outside observer – its clock would tick more slowly. So if you could accelerate a starship to just a fraction below lightspeed, it could travel for thousands of years as measured by a clock back on Earth – but just a few years or even less as measured by its own clock. So as you look at Regulus tonight, remember that the photons are completing a journey of both 79 years – and no time at all. Script by Damond Benningfield

A young planet is getting greedy. It’s gobbling up gas and dust from its surroundings. And observations last summer showed that its appetite got a lot bigger – it was consuming as much as eight times more material than in the spring. The planet is known by a catalog designation – Cha 1107. That indicates it’s in the constellation Chamaeleon, which is too far south to see from the United States. It’s hundreds of light-years away. Most planets are born in disks of material that encircle newborn stars. But this one appears to be on its own. That makes it a “rogue” world. It’s roughly five to ten times the mass of Jupiter, the largest planet in our own solar system, and about three times Jupiter’s diameter. It’s encircled by its own disk of material. That’s because it’s in a giant complex of gas and dust that’s giving birth to many new stars. As it pulls in material from its disk, it gets heavier – just like a newly forming star. The planet won’t get big enough to shine as a true star. But it’s possible that it could become a “failed” star known as a brown dwarf – a sort of missing link between stars and planets. Last summer’s outburst wasn’t the first for Cha 1107. It flared up in 2016 as well. So its growth process may be choppy – short feeding frenzies between longer periods of quieter appetite. Script by Damond Benningfield

If you’re looking for a world like Tatooine, good luck. Of the more than 6,000 known planets in other star systems, fewer than 20 orbit both stars of a binary system. So those double sunsets are few and far between. Just to refresh your memory, Tatooine is the home world of Luke Skywalker in Star Wars. Such planets are called “circumbinaries” because they circle around both stars in the system. Over the past decade, astronomers have searched for such worlds in a project with a rhythmic name: Bebop – Binaries Escorted by Orbiting Planets. The project looks for tiny “wiggles” in the motions of the stars caused by orbiting planets. It’s found a few planets, with several more candidates. One of those discoveries is Bebop-3b. The system’s two stars are quite close together. One of them is similar to the Sun. The other is only about a quarter of the Sun’s mass, and a tiny fraction of its brightness. The planet is about half the mass of Jupiter, the giant of our own solar system. It orbits the two stars once every 18 months, at a bit more than Earth’s distance to the Sun. We don’t know how fast Bebop-3b rotates, so we don’t know how often it sees sunrises and sunsets. All we know for sure is that there are two of each – one featuring a bright star, the other a faint cosmic ember. The system is about 400 light-years away. It’s high overhead at nightfall – but much too faint to see without a telescope. Script by Damond Benningfield

In the lexicon of astronomy, Pollux is known a class K-zero-3 star. That tells us that the star’s surface is a little cooler and redder than the Sun’s. It tells us that the star has puffed up to many times its original size. And it tells us that the star is nearing its end. Pollux is the brightest star of Gemini. It’s quite close to the Moon tonight. Its “twin,” the star Castor, and the brilliant planet Jupiter are a little farther from the Moon. The system that astronomers use to classify stars was developed more than a century ago. It groups the stars into classes O, B, A, F, G, K, and M. That system is based on a star’s surface temperature or color – hotter stars are bluer, while cooler stars are redder. O stars are blue-white, while M stars are red or orange. Each class is subdivided using the numbers zero through nine. At K-0, Pollux is just across the line from class G – the class that includes the Sun. The classification ends with the Roman numerals one through five. A “five” means the star is in the main phase of life. A “three” means it’s moved on to the giant phase. It’s converted the hydrogen in its core to helium. Pollux is now fusing the helium to make carbon and oxygen. That change has caused it to puff up; it’s nine times the diameter of the Sun. Over time, Pollux will get even bigger, cooler, and redder. It may evolve into class M – a brilliant star at the end of its life. Script by Damond Benningfield

Jupiter is the “big boy” of the solar system. It’s more than twice the mass of all the other planets combined. In many other star systems, though, Jupiter wouldn’t seem quite so impressive. Astronomers have discovered hundreds of planets that are heavier than Jupiter – up to 80 times Jupiter’s mass. Astronomers aren’t sure how such monster planets get to be so heavy. But they have a couple of main ideas. One says they grow from the mergers of smaller planets. The other says it depends on the environment in which a planet is born. Almost all planets take shape in disks of gas and dust around infant stars. The more material there is in the disk, the more there is for making planets. But there’s a limit on how massive a planet can become. Anything more than about 30 times the mass of Jupiter might become a brown dwarf – an intermediate step between planets and stars. And at more than 80 times Jupiter’s mass, it becomes a true star. The heavy planets don’t get much bigger than Jupiter, no matter how massive they are. As an object gains mass its gravity gets stronger. That squeezes it tighter, making it more compact. So while these “super-Jupiter” planets might outweigh Jupiter, they’d look a lot like the big boy of the solar system. Look for Jupiter near the Moon tonight. It looks like a brilliant star, so you can’t miss it. The twin stars of Gemini are close by, and we’ll have more about that tomorrow. Script by Damond Benningfield