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Dubhe

StarDate: 
February 12, 2017

When we look into the sky from here on Earth, we see one big, bright star — the Sun. All the other stars we see are mere pinpoints of light; the brightest star in the night sky looks less than a hundred-billionth as bright as the Sun.

But the residents of many other star systems would have two or more bright stars to look at it. That’s because most of the stars in the galaxy are members of systems with two stars, three stars, or even more.

An example is Dubhe, the star that marks the lip of the Big Dipper’s bowl. It’s low in the northeast as night falls right now, but wheels high across the north later on.

Dubhe actually consists of two pairs of stars.

The brighter pair is quite impressive. It includes a stellar giant — a star that’s nearing the end of its life. Changes in its core have caused its outer layers to puff up. That’s made the star about 30 times wider than the Sun, and hundreds of times brighter. Its bloated surface is relatively cool, though, so it glows bright orange.

The star’s companion is no slouch, either. It’s still in the prime of life, just as the Sun is. But it’s more massive than the Sun, so it shines brighter. And its surface is much hotter than its companion’s, so it shines pure white.

The two stars are a couple of billion miles apart — more than 20 times the distance from Earth to the Sun. Even so, if a planet orbits either star, both stars would shine brightly in its sky — giving it two “suns” for the price of one.

 

Script by Damond Benningfield

 

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