Moon, Regulus, and Saturn

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The Moon charges past the heart of the lion tonight, while the planet Saturn looks on. They're all in good view at nightfall, and remain in view for most of the night.

The lion's heart is Regulus, one of the brightest stars in the night sky. It's actually a system of three stars, but only one of them -- known as Regulus A -- is visible to the unaided eye.

The star is much hotter, brighter, and heavier than the Sun. It's also much younger -- only about 50 million years, compared to about four and a half billion years for the Sun.

Young stars tend to spin much faster than older stars, and Regulus certainly fits the profile: It completes one turn on its axis in just 16 hours, compared to almost a month for the Sun. If it spun much faster, it would actually fly apart.

The high-speed whirling makes Regulus bulge out around the equator, so it's shaped something like an onion. Since the star is much fatter through the equator than the poles, the equator is thousands of degrees cooler than the poles.

As Regulus ages, though, its magnetic field should act as a brake, slowing the star's rotation. As it slows down, it'll lose some of that bulge around the middle.

Look for Regulus quite close to the Moon tonight. At their closest, they'll be separated by about twice the width of the Moon. Bright golden Saturn is a little below them in early evening, but above them as they set around 6 or 7 in the morning.

More about Saturn tomorrow.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.