Gamma Cassiopeia

StarDate: November 4, 2009

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Cassiopeia, the queen, soars high overhead on autumn evenings. The constellation's brightest stars form a letter W. All five of those stars are bigger, heavier, and brighter than the Sun. But one outclasses the others by quite a bit.

Gamma Cassiopeia forms the middle of the W. If you add up all of its energy -- not just the light that's visible to the eye -- it shines about 40,000 times brighter than the Sun.

That's because Gamma Cas is about 15 times as massive as the Sun, and hundreds of times wider. Such a monster pumps a lot of energy into space.

It also produces a lot of energy deep in its core. The energy comes from nuclear fusion: Atoms of hydrogen stick together to make helium, releasing energy in the process.

Gamma Cas is not only big and bright, it's fast, too. Its equator spins about 150 times faster than the Sun's does. That flings hot gas out into space, where it forms a "doughnut" around the star. The size and thickness of the doughnut change, making Gamma Cas look fainter or brighter. Back in the 1930s, it shined several times brighter than it does today.

And in the distant future, it'll shine even brighter -- for a while. Because of its great heft, it's likely to explode as a supernova. For a few days or weeks, it'll outshine everything in the night sky except the Moon.

Cassiopeia has produced two other supernovae in recent centuries, and we'll talk about those tomorrow.

Script by Damond Benningfield, Copyright 2009

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