Capella

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A remarkable star system stands high overhead this evening. Its main components are two giant stars that are nearing the ends of their lives.

The star system is Capella, the she-goat, in the constellation Auriga. The light from its twin giants blurs together into a single point, forming one of the brightest stars in the night sky.

The stars are classified as giants because each is dozens of times brighter than the Sun. Each is also about 10 times bigger than the Sun, and more than twice as massive.

The stars are quite close together -- only about two-thirds as far from each other as Earth is from the Sun. It's unlikely that planets could form around either star individually, although planets could orbit the combined pair. So far, though, no one has found evidence of planets in the Capella system.

The "giant" classification indicates that the stars are going through their final stages of evolution.

For most of their lives, the stars "burned" the hydrogen in their cores to make helium. Now, they've gone past that stage. They've used up their hydrogen, so they're burning their helium -- or they're about to burn it -- to make even heavier elements. This process has caused their outer layers to puff up, making the stars bigger and brighter.

Eventually, the stars will cast these layers into space, leaving behind only their hot, dense cores -- a pair of "white dwarfs" that will slowly cool and fade from sight.

Script by Damond Benningfield, Copyright 2004, 2007

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