Moon and Regulus

• ‹ Previous program
• 350 of 1997
• Next program ›

The Moon has a close encounter of the stellar kind tonight. It passes within a couple of degrees of Regulus, the star that marks the heart of Leo, the lion. They rise in late evening, and stand high in the sky at dawn.

Even though Regulus is fairly close by, astronomers are still learning about the star as they study it with new instruments and techniques.

In 2004, for example, they discovered that Regulus isn't round. Instead, it's about a third thicker through the equator than through the poles, so it's shaped like a flattened beach ball.

Regulus is squashed because it spins rapidly. In fact, if it spun just a little faster, it would fling itself apart.

Earlier this year, a team led by Douglas Gies of Georgia State University discovered the likely cause of this rapid rotation: a faint companion star that whirls around Regulus every 40 days.

The newfound star is probably a white dwarf -- the small, hot, dense corpse of a once-normal star, like Regulus itself.

As this companion neared the end of its life, it puffed up to form a red giant. It may have grown so large that it spilled much of its gas onto Regulus. As that happened, the star transferred some of its orbital momentum to Regulus, making Regulus spin much faster -- fast enough to give the star a bulging waistline.

Look for Regulus just a little to the left of the Moon as they rise tonight, with the Moon moving even closer during the night.

Script by Ken Croswell, Copyright 2008

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