Moon and Regulus

Regulus, the bright heart of Leo, the lion, shines close to the gibbous Moon the next couple of nights. The star is below the Moon as they climb into view by midnight tonight.

The name “Regulus” means “the little king.” Yet it’s not so much a monarch as a ruling quartet. That’s because Regulus appears to consist of not one star, but four.

Only one of them is bright enough to see with the unaided eye — the one we know as Regulus. But it has a close companion that once shined even brighter.

This companion was heavier than Regulus’s bright star, Regulus A, so it aged more quickly. As it neared the end of its life, it puffed up. Much of the gas in its outer layers poured over onto Regulus A. That made the star bigger and brighter, and made it spin much faster. When the companion’s outer layers were gone, all that was left was its dead core: a white dwarf — a super-dense ball that’s a third as massive as the Sun, but only about the size of Earth.

Regulus has two other companions, but they’re a long way from the bright star — about 4,000 times farther than Earth is from the Sun. They form a widely separated pair. One of the stars is a bit smaller and cooler than the Sun. The other is a bare cosmic ember. From the system’s distance of 78 light-years, you need a telescope to see even the combined light of these two stars — faint companions to the lion’s mighty heart.

Tomorrow: a changing constellation.

Script by Damond Benningfield