Moon and Regulus
Many hundreds of stars twinkle across the sky tonight. Like our own star, the Sun, they're big balls of gas that shine through nuclear reactions in their cores.
But many of the stars visible to the unaided eye are different from the Sun in a couple of key ways. First, a lot of them are much bigger and more massive than the Sun, so they shine a lot brighter. And second, most of them are members of stellar families -- they have one or more sibling stars.
One example is Regulus, the "heart" of Leo, the lion. It's just a whisker to the lower left of the Moon at first light tomorrow.
The star that we see as Regulus -- known as Regulus A -- is about three and half times as big and massive as the Sun. That means it consumes the fuel in its core much faster, so it "burns" hotter than the Sun. In turn, that makes Regulus shine scores of times brighter than the Sun.
And the star has at least two companions, known as Regulus B and C. One of the stars is a little less massive than the Sun, while the other is much less massive. As a result, they both shine so meekly that they're invisible to the unaided eye -- you need a telescope to see them.
The Regulus system isn't a very close-knit family, though. The two smaller stars are about a hundred times farther from Regulus A than Pluto is from the Sun. From that distance, Regulus A would shine in their night skies like a brilliant sapphire -- the bright, hot jewel of the Regulus system.
Script by Damond Benningfield, Copyright 2008
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