Moon and Regulus

StarDate: May 29, 2009

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Most of the stars we see in the night sky aren't alone. Although they look like single pinpoints of light, they're really families of two stars or more.

An example is Regulus, the brightest star of Leo, the lion. It's a little to the upper left of the Moon as darkness falls this evening.

Regulus consists of at least four stars.

The brightest of the bunch is Regulus A. It's a good big bigger, heavier, and hotter than the Sun. It's nearing the end of its "normal" lifetime, and will soon undergo a series of changes. First it'll puff up like a balloon, getting much bigger and brighter than it is now. Then its outer layers will drift off into space, leaving only its hot but tiny core -- a white dwarf.

That's already happened to one of the other stars in the system. It's a very close companion -- so close that when it puffed up, Regulus A siphoned off a lot of its gas. As the gas fell onto Regulus A, it began spinning faster. Today, it spins so fast that it bulges out at the equator, so it's shaped like a big pumpkin.

The other companions don't have to worry about the same thing happening to them, though. They're hundreds of billions of miles from Regulus A. From Regulus A, they look like brilliant yellow or orange pinpoints of light.

What they lack in showiness, though, they'll make up for with longevity. They'll continue to shine for billions of years after Regulus A becomes a white dwarf and fades from view.

Script by Damond Benningfield, Copyright 2009

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