Eta Leonis

StarDate: March 14, 2009

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Looks can deceive -- including in the night sky. Tonight, one of the most powerful stars sails overhead, but you'd never know it just by looking at it.

The star is part of the large constellation Leo, the lion. Leo's brightest star is Regulus, which is so bright you can see it even through light-polluted city skies. Regulus is well up in the east early this evening, and climbs across the south during the night.

Due north of Regulus is a star that looks fainter, but is actually a hundred times brighter.

The star is called Eta Leonis. It's much farther from Earth than Regulus is. Regulus is less than 80 light-years away, while Eta Leonis is about 25 times farther. That we can see it from such a great distance tells us that Eta Leonis is one powerful star. If Regulus or the Sun were that far away, we'd never be able to see them with just the unaided eye.

Eta Leonis is classified as a white supergiant. It emits roughly 14,000 times more light than the Sun does. At that rate, the star produces more light in a single hour than the Sun does in a year and a half. The reason for its great power is simple: It's more massive than the Sun. As a result, its core must produce enormous amounts of energy to hold up the star's own weight.

But Eta Leonis will pay a high price for its showiness. Within just a few million years, this brilliant star will run out of fuel and die -- while Regulus and the Sun shine on.

Tomorrow: the king of the planets.

Script by Ken Croswell, Copyright 2009

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

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