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

Elnath has dual citizenship. Officially, it’s the second-brightest star of Taurus, so it’s known as Beta Tauri. It marks the tip of one of the bull’s horns. But it’s also known as Gamma Aurigae – one of the bright stars that outlines Auriga, the charioteer. That designation is un-official – it’s been considered defunct for almost a century. The dual identity is a result of changes in how astronomers define the constellations. At first, the constellations were vaguely defined. Each one encompassed the connect-the-dots pattern that outlined the classical figure. But there weren’t hard borders. In 1603, German astronomer Johannes Bayer published a new naming scheme for all the stars. In it, he assigned Elnath to both Taurus and Auriga. That worked fine for centuries. But in the early 20th century, astronomers decided to assign precise boundaries for each constellation – like the borders of states or nations. Elnath was just inside the border of Taurus. So, officially, Elnath belongs to the bull. But it still forms part of the classical outline of Auriga – giving Elnath a dual citizenship. Elnath is about 130 light-years away. It’s about five times the size and mass of the Sun, and it’s hundreds of times brighter. It’s easy to pick out tonight because it’s close to the Moon. As night falls, they’re no more than one or two degrees apart – right along the border between the bull and the charioteer. Script by Damond Benningfield

Just about every star is born in a cluster – a family of dozens to thousands of stars. Most of these families fall apart, with the individual stars going their own way. The Sun’s cluster, for example, dissipated billions of years ago. One cluster that’s in the process of dissipating is the Hyades, which outlines the face of Taurus, the bull. It’s the nearest cluster, at a distance of about 150 light-years. Today, the Hyades contains several hundred stars – probably less than half its original population. The other stars were pulled away by the gravitational tug of the rest of the galaxy. The cluster’s heaviest stars reside in its tightly packed center. None of them is much more than about twice as massive as the Sun. That’s because of the cluster’s age – 625 million years. All of its heavier stars have already burned out. All that remains is their dead cores. The least-massive stars have migrated to the outskirts of the cluster. Over the next few hundred million years, those stars will all drift away. That will leave only a sad little remnant of this impressive family of stars. The Hyades stands to the lower left of the Moon this evening. Its stars form a “V” shape. The brightest star in the outline is bright orange Aldebaran, the bull’s eye. But it’s not a member of the cluster – it simply lines up in the same direction as the stars of the Hyades. We’ll have more about the Moon and Taurus tomorrow. Script by Damond Benningfield

For the kings of ancient Egypt, the Sun was much more than just a glowing orb in the daytime sky. It was the god Ra, one of the most important of all the gods. Ra was a creator of life, the king’s father, and a representation of the king as a god himself. So the kings of the Fifth Kingdom, about 4500 years ago, built temples to honor the Sun. Archaeologists have recently excavated about half of the largest one yet discovered – a massive complex that might have been topped by a spot for watching the Sun and stars. The temple is named “Joy of Ra” or “Joy of the Heart of Ra.” It’s at Abu Gorab, about 10 miles from Cairo, near the ancient capital, Memphis. It was built by King Nyuserre, who reigned for two or three decades. At the time, the kings identified themselves with Ra – as eternal gods. So the temple was a place to honor both Ra and the king. Excavations have uncovered two large enclosures. The upper level was discovered 125 years ago, but the lower one was found just recently. The upper level included an altar for making offerings to Ra. And one end featured an obelisk that would have towered high above the courtyard and the surrounding landscape. It had a perfect east-west alignment – the directions of the rising and setting Sun. The recent work also uncovered a stairway to the roof. The rooftop probably served as an observatory – helping Nyuserre follow his “father” across the sky. Script by Damond Benningfield

An astronomer greets visitors to a science museum in Canberra, Australia. He’s made of riveted iron plates, and he stands atop a wide ring, gazing skyward through a smaller ring in his right hand. He’s the last remnant of an historic telescope that was destroyed in a massive wildfire. The fire blazed across Australia in January of 2003. It destroyed most of Mount Stromlo Observatory, one of the major astronomy research centers in the southern hemisphere. The fire consumed five telescopes, plus a laboratory where scientists and engineers built astronomical instruments. One of the casualties was the Yale-Columbia Telescope. It was a 26-inch refractor – a type of telescope that uses lenses to gather and focus starlight. It was built in 1924, and had been operating at Mount Stromlo for half a century. Astronomers had used it to measure the distances to stars, to study double stars, and more. After the fire, an Australian science institute commissioned a sculptor, Tim Wetherell, to create an artwork from the telescope’s remains. The result was “The Astronomer” – the piece on display in Canberra. The figure stands on a setting circle – a wide ring that indicated where the telescope was pointing. It has numbers at 10-degree intervals, from zero to 180. The astronomer is holding a smaller version of the ring in his hand – continuing to look at the stars long after the telescope’s demise. Script by Damond Benningfield

The crescent Moon and the planet Venus team up in the evening twilight tonight. Venus is the brilliant “evening star.” It’s below the Moon, and it sets by the time the sky gets fully dark. Venus is enveloped by an unbroken layer of clouds – one of the reasons the planet looks so bright. The clouds are a few dozen miles above the surface. And they’re speedy – they race around the planet at up to 335 miles per hour – twice as fast as the winds in a category-5 hurricane. They make a full turn around Venus every four days. That’s more than 50 times faster than the planet is turning on its axis. That high-speed motion is called super-rotation. No one knows for sure what causes it. A study a few years ago said it might be powered by the Sun. The clouds are hottest at the equator, where the sunlight is strongest. The hotter atmosphere flows outward, toward the poles and toward the nightside – reaching super-fast speeds. Super-rotation doesn’t extend all the way to the surface, though. Below the clouds, the wind speed drops dramatically. At the surface, there’s almost no wind at all. But the atmosphere is quite dense – more than 90 times the density of Earth’s atmosphere. Any wind at all exerts a lot of pressure, so it can erode the surface. That can wear away mountains, and gouge channels that look like they were carved by flowing water – all below the speedy clouds of the planet Venus. Script by Damond Benningfield