Future Sun

StarDate: November 10, 2009

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Astronomers may not be fortune tellers, but they can tell us what the future will be like for the Sun. In fact, they can even show us -- just by pointing to the ruddy "eye" of Taurus, the bull.

That bright orange star is Aldebaran, which is in good view in the east by about 8 or 9 p.m. It's nearing the end of its life, so it's undergoing a series of dramatic changes -- the same changes the Sun will go through in several billion years.

For most of its life, Aldebaran did just what the Sun is doing now -- it "fused" the hydrogen atoms in its core to make helium, releasing enormous amounts of energy in the process.

Eventually, though, it used up the hydrogen. The core shrank and got hotter, while the star's outer layers puffed up like a balloon. They also got cooler, so the star shines with a distinctly orange color.

And that's about where things stand now. Aldebaran is so puffed up that if it took the Sun's place in our solar system, it would extend about halfway out to the orbit of Mercury, the innermost planet.

Aldebaran probably hasn't started fusing its helium to make carbon, the next-heavier element. But that'll happen fairly soon. And when all the helium is gone, the fusion reactions will stop. The star's outer layers will blow away into space, exposing the hot, dead core -- a white dwarf.

Over the eons, the white dwarf will slowly cool and fade -- just as the Sun will do when it reaches the end of its own long life.

Script by Damond Benningfield, Copyright 2009

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