Adhara

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StarDate: January 30, 2014

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There’s more than one way to look at the stars. With our eyes alone, we see only a tiny sliver of the spectrum of energy they release into space. But our instruments see the entire spectrum. And as we tune up and down that spectrum, different forms of energy become more prominent.

Consider Adhara, the second-brightest star of Canis Major, the big dog, which is in the southeast by mid-evening.

The constellation’s brightest star is Sirius — the brightest star in the night sky at visible wavelengths. Adhara is to its lower right. In reality, it’s thousands of times brighter than Sirius. It looks much fainter, though, because it’s hundreds of light-years farther.

Even so, if you could tune your eyes to the ultraviolet, Adhara would far outshine Sirius. In fact, it would be the brightest star in the night sky.

That’s because Adhara is quite hot. At such high temperatures, a star produces most of its energy not in the form of visible light, but as ultraviolet. Adhara is also big, so there’s a lot of surface area to radiate energy into space. The combination of size and temperature makes Adhara a brilliant ultraviolet beacon.

That won’t always be the case, though. In a few million years, changes in the star’s core will cause its outer layers to puff up. As they do, they’ll get much cooler, so Adhara’s ultraviolet light will be extinguished. Instead, the star will blaze in another band of energy — one of the brightest infrared sources in the sky.

 

Script by Damond Benningfield, Copyright 2013

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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