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Moon and Regulus

February 27, 2010

A kingly star accompanies the full Moon across the sky tonight. Although it's the leading light of Leo, its name doesn't have anything do with the lion. Instead, Regulus means "the little king" -- a name handed down from ancient Mesopotamia.

Regulus is bigger, hotter, and brighter than the Sun, which is why it shines brightly in our sky even though it's about 79 light-years away. But stripped down to it basics, it's a lot like the Sun.

Both are classified as "main-sequence" stars. That means that both are in the prime of life, burning through the hydrogen gas in their cores to make helium. This process, known as nuclear fusion, releases enormous amounts of energy, which is what makes the stars shine.

Because Regulus is more than three times the Sun's mass, though, it's consuming its hydrogen much faster, so it'll move off the main sequence much more quickly. It'll stay on the main sequence for less than half a billion years, versus more than 10 billion years for the Sun.

Despite the difference in mass, the same fate awaits both stars. When they've used up their hydrogen, they'll puff up to gigantic proportions. Then they'll cast their outer layers into space, leaving only their hot, dense cores -- cosmic embers that will slowly cool and fade away.

Look for Regulus just a bit to the upper left of the Moon at nightfall, and sticking close to the Moon throughout the night.

More about the Moon and its companions tomorrow.

Script by Damond Benningfield, Copyright 2009

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