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January 30, 2012

Venus shines in the southwest as the sky gets dark tonight. It’s the brilliant “evening star,” so you can’t miss it. Despite its nickname, Venus isn’t really a star at all — it’s a planet — the brightest one visible in all the night sky.

The brightest true star in the night sky is low in the southeast at the same hour: Sirius, the leading light of Canis Major, the big dog. The “Dog Star” arcs across the south during the night, and sets in the wee hours of the morning.

Sirius looks so bright for a couple of reasons. For one thing, it really is a fairly bright star — more than 25 times brighter than the Sun. And for another, it’s less than nine light-years away, which makes it one of our closest stellar neighbors.

Sirius shines so brightly in part because its surface is thousands of degrees hotter than the surface of the Sun, which gives it a pure white color.

When combined with the star’s size and mass, the temperature tells us that Sirius is burning through the hydrogen fuel in its core in a hurry. As a result, it’ll live a much shorter life than the Sun will. When its fuel is used up, the star will cast its outer layers into space, leaving behind only its small and dense but extremely hot core: a white dwarf.

That fate has already befallen a companion to Sirius, which is too faint to see through the glare of Sirius itself without a telescope. In fact, a telescope maker discovered the companion just 150 years ago. More about that tomorrow.


Script by Damond Benningfield, Copyright 2011


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