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December 26, 2018

Over the centuries, we’ve given the visible stars many names — proper names, catalog designations, and others. But one star is best known not by any of its formal names, but by its nickname: the Dog Star. Its proper name is Sirius. It’s the leading light of 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 brilliance is because Sirius is a couple of dozen times brighter than the Sun. But part of it is because Sirius is a close neighbor — less than nine light-years away. Only five other stars systems are closer.

And thanks to the relative motions of Sirius and the Sun, Sirius is inching closer — at about 17,000 miles per hour — about as fast as the International Space Station orbits Earth. It’ll continue to close in for tens of thousands of years. But the distances between the stars are so huge that even at that speed, Sirius won’t get much brighter.

Astronomers discovered the star’s motion toward us by measuring its redshift — a slight change in the wavelengths of its light. That 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 about 8:30 or 9. It’s the brightest star in the night sky, so you can’t miss it.

Script by Damond Benningfield

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