StarDate

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