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Proxima Centauri

September 10, 2015

You might expect our closest neighboring star to be one of the brightest lights in the night sky. Instead, though, it’s so faint that it wasn’t discovered until a century ago this month. Now known as Proxima Centauri, it’s just four-and-a-quarter light-years away.

If all the stars were as bright as the Sun, nearby stars would be easy to find, because they’d shine the brightest. But most stars are red dwarfs, which are so faint that not a single one is visible to the unaided eye.

Robert InnesRobert InnesProxima Centauri was discovered by Robert Innes. He was born in Scotland but journeyed to South Africa to observe the southern sky. He made his great find by examining photographic plates taken on two different nights — one in 1910 and the other in 1915. Innes alternated the view from one plate to the other. In this way, he spotted a dim star that shifted position during the five-year interval — a sign the star was close by.

The new star was quite close to Alpha Centauri, which was the closest-known star system. What’s more, the new star seemed to be moving in the same direction as Alpha Centauri, which suggested they might be related. Sure enough, when astronomers measured it, they found it was nearly the same distance as Alpha Centauri.

It turns out that the star is actually a member of the Alpha Centauri system. But it’s a bit closer to us than the system’s other two stars, hence its name: Proxima Centauri, the closest star to the Sun.

More tomorrow.


Script by Ken Croswell, Copyright 2015

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