The Moon is a tale of two faces. The side we see – the nearside – features giant volcanic plains and a fairly thin crust. The far side features more mountains and craters and much thicker crust. And the differences might go even deeper. The layer below the crust – the mantle – might be cooler on the farside – or was cooler billions of years ago. That difference is suggested by samples returned to Earth by a Chinese lander – the first samples from the farside. Some of the samples formed from molten rock. It cooled and solidified 2.8 billion years ago, deep inside the Moon. Details about the samples suggest the molten rock was much cooler than the same layer on the nearside – by about 200 degrees Fahrenheit. That’s probably because the far side has fewer radioactive elements, which heat the interior as they decay. Just why that’s the case isn’t clear. A smaller moon might have splatted into the lunar farside when the Moon was young. Or a giant asteroid impact might have moved things around. The pull of Earth’s gravity might have played a role as well. Whatever the cause, there’s a big difference in the lunar hemispheres – which may be more than skin deep. The gibbous Moon is passing through the constellation Taurus tonight. Aldebaran, the bull’s eye, is to the right of the Moon at nightfall. And Elnath, at the tip of one of the bull’s horns, is closer to the lower left of the Moon. Script by Damond Benningfield

In Greek mythology, Chiron was the wisest of the centaurs – creatures who were half human and half horse. He taught other centaurs about medicine, botany, and other sciences. Today, the astronomical Chiron is teaching scientists about the formation and evolution of ring systems. Chiron is one of about a thousand known centaurs – chunks of ice and rock between the orbits of Jupiter and Neptune. It’s one of the larger ones, at an average diameter of about 125 miles. Even so, it’s so far away that it’s tough to study. But it sometimes passes in front of a distant star. Such a passage allows scientists to measure its size. It also allows them to study the space around Chiron. Rings cause the light of the background star to flicker. Observing that effect from different locations, and at different times, provides a profile of the rings. A study last year reported some changes. Scientists already knew of three rings. The new study reported evidence of a fourth ring. It’s so far out that Chiron’s weak gravity might not be able to hold it. The scientists also found a wide disk of dust. The rings and disk might be debris from a small moon, or the result of an outburst from Chiron itself. Chiron is moving closer to the Sun. As it warms up, it could produce more outbursts. So the system could undergo more big changes in the years ahead – teaching us much more about the evolution of rings around the small bodies of the solar system. Script by Damond Benningfield

The realm of the giant outer planets is like a transit station for some smaller bodies. They come from beyond the orbit of Neptune, the solar system’s most remote major planet. And like passengers at a hub airport, their destinations are all over the map. These objects are called centaurs. Like the half-human, half-horses of myth, they’re hybrids – they look like both asteroids and comets. Most of them are quiet chunks of rock and ice, like asteroids. But some have haloes or tails of gas, like comets. Centaurs orbit the Sun between Jupiter and Neptune. And their orbits cross those of at least one of the giant planets. They’re small and far away, so they’re hard to find. Even so, astronomers have discovered about a thousand of them. And there could be as many as a hundred thousand that are at least a kilometer across. Centaurs come from a belt of debris beyond Neptune. They’re nudged inward by Neptune’s gravity. None of them will spend more than a few million years in the realm of the giants, though. Instead, the gravity of the planets will give them a kick. Some will be booted out of the solar system. Others will be pushed into the inner solar system. And others will slam into a planet. The biggest centaur is Chariklo. It’s about 160 miles in diameter, and it has a couple of rings. The first centaur ever seen, Chiron, also has rings. And it’s growing new rings even now. More about that tomorrow. Script by Damond Benningfield

Many of the features on the Moon are named for astronomers. So are features on Mars and other planets and moons. And hundreds of asteroids are named for astronomers as well. But you won’t find many features named for astronomers here on Earth. Quite a few streets and schools are named after them. But when it comes to major features, the list is pretty thin – especially in the United States. One of the few is Mount Langley, a 14,000-foot summit in California. It’s named for Samuel Pierpont Langley, who was a long-time director of the Allegheny Observatory. To see more features named for astronomers, though, you need to head south – to Australia, New Zealand, and even Antarctica. In Australia, for example, a river and an estuary are named for Thomas Brisbane, an early governor of the state of New South Wales. And so is the city of Brisbane, the capital of Queensland. In addition to his government duties, Brisbane was an astronomer. He set up Australia’s first major observatory. In New Zealand, several peaks in a large mountain range are named for astronomers, including Galileo and Copernicus. And an entire range is named for Johannes Kepler. In Antarctica, many features are named for James Ross, an early explorer. But Ross himself named several features for astronomers, including Cape Smyth and Mount Lubbock – down-to-earth features named for men who studied the stars. Script by Damond Benningfield

When a dying Sun-like star exhales its final breath, it’s a doozy. The star blows its outer layers of gas into space. That surrounds the star’s dying core with a colorful bubble. The bubble can last for tens of thousands of years before it fades away. One of those bubbles is on the edge of Gemini, which is well up in the east at nightfall. Known as the Medusa Nebula, the bubble is about 1500 light-years away, and it spans more than four light-years. It’s named for one of the Gorgons of Greek mythology. That’s because some of its tendrils of gas have reminded skywatchers of the snakes on Medusa’s head. Those tendrils have been expanding into space for thousands of years. They began their journey when their star could no longer produce nuclear reactions in its core. Gravity squeezed the dying core tighter, making it smaller and hotter. The radiation of the hotter core pushed away the layers of gas around the core. Today, they’re moving outward at more than 30 miles per second. Ultraviolet light from the core “energizes” the gas in the nebula, making it glow like a fluorescent bulb. Different elements glow in different colors. That tells astronomers about the original star, and about the process of its demise. The fate of the Medusa Nebula is shared by all Sun-like stars. So billions of years from now, the Sun will create its own nebula – a colorful bubble blown with its dying breath. Script by Damond Benningfield

There just aren’t enough superlatives to describe the galaxy OJ 287. It’s a quasar – an especially bright object powered by two supermassive black holes. One of them is about 150 million times as massive as the Sun. The other is 18 billion times the Sun’s mass – one of the heaviest black holes yet seen. They team up to produce outbursts that are a trillion times brighter than the Sun – brighter than all the stars in the Milky Way Galaxy combined. OJ 287 is always bright. But every few years, it flares up – the result of interactions between the black holes. Each of them is encircled by a giant disk of gas. As the gas spirals in, it gets extremely hot. That makes the disks extremely bright. The smaller black hole orbits the larger one every 12 years. The orbit is tilted. So every six years, the black hole plunges through the disk around the larger black hole. That can heat some regions to trillions of degrees, producing the flare-ups. Astronomers recently used radio telescopes to take a picture of the system. They saw a long “jet” of particles from the smaller black hole. The jet is twisted by the interactions between the black holes – confirming the profile of this amazing system. OJ 287 is in Cancer, which is low in the east at nightfall. Even though it’s billions of light-years away, OJ 287 is bright enough to see through most amateur telescopes. Script by Damond Benningfield

Saturn’s rings are among the most beautiful features in the solar system – and the most mysterious. Scientists continue to debate how and when the rings formed, and how much longer they might hang around. But the rings aren’t Saturn’s only beautiful and mysterious feature. An almost perfect hexagon of clouds wraps around the planet’s north pole. And scientists continue to debate how it formed and what keeps it going. Saturn is the second-largest planet in the solar system – nine-and-a-half times the diameter of Earth. So the hexagon is giant as well – more than twice as wide as Earth. And it’s long-lasting – it was first observed in 1981. There are several ideas about what shapes the hexagon. Perhaps the leading idea says that winds deep in the atmosphere blow at different speeds at different latitudes. As these jet streams rub against other, they create waves that ripple to the top of the clouds. Those clouds form regular patterns – the sides of the hexagon. There’s one other mystery about the hexagon: It appears only at the north pole, not the south. So scientists are still working to explain this beautiful feature at the top of a beautiful planet. Saturn poses near the Moon the next couple of evenings. It looks like a bright golden star. It’s to the upper left of the Moon tonight, and a bit farther below the Moon tomorrow night. Tomorrow: a system that defies description. Script by Damond Benningfield

Orion climbs high across the sky on winter nights. It’s in the east-southeast at nightfall, and it’s easy to pick out. Look for the constellation’s “belt” – a short line of three stars that points straight up. In ancient Greece and Rome, Orion was known as a mighty hunter. But in ancient Egypt, the figure was even mightier. It represented Osiris, the god of the underworld. In fact, he was thought to reside in the stars of the belt. The story of Osiris dates to Egypt’s Old Kingdom, at least 4500 years ago. It says that Osiris was a great king. But he was murdered and chopped apart by his brother, Set. Isis, Osiris’s wife and sister, recovered the pieces, wrapped him in bandages, and used a magic spell to resurrect him. She then gave birth to Horus, who avenged his father by killing Set. As a god, Osiris reigned over the underworld. When the Sun passed through the underworld at night, Osiris gave new life to the Sun god, Re. So he became known as the god of rebirth and resurrection. He was associated with the start of a new year, when the Nile brought lifegiving floods to the fields. When a king died, he joined Osiris in the stars. Some researchers have suggested that a shaft in the Great Pyramid of Giza aimed toward Orion’s Belt at the time it was built. Others say there’s no astronomical significance to the shaft. But just about everyone agrees that Orion’s Belt was considered the resting place of Osiris. Script by Damond Benningfield

Orion is a land of monsters. It’s packed with stars that are among the most impressive in the galaxy – they’re big, heavy, and bright. Even among all those superstars, though, Lambda Orionis stands out. It consists of two monster stars. The largest is about 35 times the mass of the Sun, and perhaps 200 thousand times brighter. Orion is home to so many major stars because it’s on the leading edge of a spiral arm – a zone where many new stars are being born. Lambda belongs to a cluster that’s one hotbed of starbirth. It contains many stars of all sizes and masses. Lambda’s main star is the brightest and heaviest in the cluster. The cluster is encircled by a ring of gas and dust – probably outlining the shockwave of a massive star that exploded as a supernova. Lambda’s radiation zaps the material in the ring, making it glow. Lambda is only a few million years old, yet its time is almost up. Because it’s so massive, it will live a very short life. Soon, it may explode as a supernova, with its core collapsing to form a black hole. On the other hand, it might be massive enough for the entire star to become a black hole, with no explosion at all – a monstrous ending for a monster star. Orion is in the east and southeast at nightfall. Bright orange Betelgeuse marks its left shoulder. Lambda is to the upper right. Despite its true brilliance, it looks fainter than many of the hunter’s other impressive stars. Script by Damond Benningfield

For a while now, astronomers have suspected that Betelgeuse has a companion. And they might have found it. If it really exists, though, it won’t be around for long. Betelgeuse is a supergiant. It’s about 15 times as massive as the Sun, hundreds of times wider than the Sun, and tens of thousands of times brighter. There’s a wobble in the star’s light that lasts about six years – possibly caused by the gravity of a smaller companion star. A team looked for the companion in 2020 and 2024. The team stacked thousands of short-exposure images together, producing a sharp view of the system. The researchers didn’t see anything in 2020 – but they hadn’t expected to. The two stars were predicted to be too close together to tell them apart. But the team did see the companion in 2024, when the stars were farther apart. If the star really exists, it would be a little bigger and heavier than the Sun. But it’s so close to Betelgeuse that it’s enveloped in the supergiant’s outer atmosphere. That’s pulling the star closer in. Eventually, it should get so close that the gravity of Betelgeuse will rip it apart. And even if that doesn’t happen, before long Betelgeuse will explode as a supernova – bad news for both stars. Betelgeuse is the bright orange shoulder of Orion the hunter. It’s a third of the way up in the east-southeast at nightfall, to the left of Orion’s Belt. More about Orion tomorrow. Script by Damond Benningfield