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December 29, 2012

Over the centuries, we’ve given all the visible stars many names — proper names, catalog designations, and others. But only one star is best known not by any of its formal names, but by its nickname: the Dog Star. Its proper name is Sirius, and it’s the leading light of the constellation Canis Major, the big dog — hence the nickname.

Sirius is so well known because it’s the brightest star in the night sky — its closest competition is only about half as bright. Part of that is because Sirius itself is a couple of dozen times brighter than the Sun. But part of it is because Sirius is one of our closest neighbors — it’s less than nine light-years away.

And thanks to the relative motions of Sirius and the Sun around the center of the galaxy, Sirius is moving closer, at about 17,000 miles per hour. It’ll continue to close in on us for tens of thousands of years. But the distances between stars are so enormous that even at that high rate of speed, Sirius won’t grow much brighter in our sky.

Astronomers discovered the star’s motion toward us by measuring its Doppler shift — a slight change in the wavelength of its light. The Doppler shift also allowed them to measure the orbit of a faint companion — a stellar corpse known as a white dwarf; more about that tomorrow.

In the meantime, look for Sirius climbing into good view in the east-southeast by around 8:30 or 9. It’s the brightest star in the night sky, so you can’t miss it.


Script by Damond Benningfield, Copyright 2012

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