Moon and Antares

StarDate: September 23, 2009

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Two stars that are on opposite ends of the stellar temperature scale huddle close to the Moon this evening. One of them is so bright, though, that it cloaks the other from view, so all we see is a single orange point of light: Antares, the heart of the scorpion. It's low in the southwest as night begins to fall, a little to the upper left of the crescent Moon.

Technically, the two stars are known as Antares A and B. The "A" star is the one that's visible to the unaided eye. It's one of the mightiest stars in the galaxy -- a supergiant that's more than a quarter of a billion miles in diameter.

Antares A looks orange because its surface is fairly cool -- several thousand degrees cooler than the Sun, in fact. The lower temperature means that most of its energy is in the form of infrared energy. We can't see the infrared, but we feel it as heat. So to the eye alone, Antares A is about 10,000 times brighter than the Sun. But when you toss in the infrared, it's at least 60,000 times brighter.

Antares B is at the opposite end of the scale. Its surface is blue-white, which means it's tens of thousands of degrees hotter than the Sun. Most of its energy is in the ultraviolet -- the type of energy that causes sunburn. It, too, is much bigger than the Sun. But it's much smaller than Antares A, so it doesn't look as impressive. You need binoculars to pluck it from the glow of its mighty companion.

More about Antares tomorrow.

Script by Damond Benningfield, Copyright 2009

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