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Moon and Aldebaran

August 7, 2015

The Moon slides past a couple of bright orange stars over the next few nights. The first is Aldebaran, the eye of Taurus, the bull. It’s to the lower left of the Moon at first light tomorrow. The other is Betelgeuse, one of the shoulders of Orion, which is far below Aldebaran.

In some ways, the two stars are similar. In others, though, they’re quite different.

Both stars are nearing the ends of their lives. Changes in their cores have caused their surfaces to puff outward, swelling the stars to many times their original size. That’s caused their outer layers to get cooler, which is why Aldebaran and Betelgeuse look orange — the cooler a star’s surface, the redder its color.

But there’s a lot more on the “different” side of the ledger.

Aldebaran is almost twice as massive as the Sun, while Betelgeuse is about 10 times heavier still. Heavier stars puff up much more during their final stages, so Betelgeuse is roughly 20 times wider than Aldebaran. And because Betelgeuse is so much bigger, it shines roughly 2,000 times brighter.

And there’s one other difference between them. Aldebaran will eventually cast off its outer layers, leaving a hot, dense core known as a white dwarf. But Betelgeuse will blast away its outer layers in a titanic explosion known as a supernova. And its remnant core will be squeezed much tighter, forming a neutron star — an object that’s heavier than the Sun, but no bigger than a small city.


Script by Damond Benningfield, Copyright 2015

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