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Moon and Aldebaran

July 8, 2010

The stars are constantly changing. The Sun, for example, is "fusing" together hydrogen in its core to make helium. As it consumes the hydrogen, the core shrinks and gets hotter. The extra energy pushes on its outer layers, making the Sun get bigger. It's a gradual process, though -- it takes tens of millions of years to notice any difference.

A star that lines up near the Moon at dawn tomorrow is also going through some changes, but at a much faster rate.

Bright orange Aldebaran, the leading light of Taurus, the bull, is to the right or lower right of the Moon at first light.

Aldebaran is much farther along in its life cycle than the Sun is. It's consumed its original hydrogen, so its core is made of helium.

Right now, Aldebaran appears to be in a fairly quiet phase. The core is shrinking, and the temperature is getting hotter. Eventually, it'll get hot enough to trigger the next set of nuclear reactions, in which the helium fuses together to make carbon.

As the core heats up, it pumps more energy into the layers of gas around it, causing them to expand. Right now, Aldebaran is more than 40 times wider than the Sun. Over the next few million years, though, it's likely to get much bigger -- and shine much brighter.

Even now, though, Aldebaran is no slouch. It's one of the brightest stars in the night sky. Look for it to the right or lower right of the Moon at dawn.

We'll talk about two bright lights in the evening sky tomorrow.

Script by Damond Benningfield, Copyright 2010

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