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June 9, 2014

If you judge by the layout of the night sky, you might think that centaurs roamed across every field and mountain in ancient Greece. That’s because these mythological beasts are represented by not one, but two constellations created by the Greeks.

One of them is Sagittarius, the archer, which rises in the southeast before midnight from most of the United States. The other is simply Centaurus, the centaur. Much of it isn’t visible from the U.S. at all. It’s best viewed from the far-southern reaches of the country, where his head and shoulders — his human half — stand due south at nightfall.

The brightest star in that part of the constellation is Menkent, the centaur’s shoulder. The star is nearing the end of its life, so its outer layers have puffed up, making Menkent a good bit bigger and brighter than the Sun.

Astronomers have been able to get an accurate measurement of Menkent’s distance. They used a technique called parallax, where they measured the precise direction to the star when Earth was on opposite sides of the Sun.

The technique is like holding a finger close to your face and looking at it with first one eye, then the other — the finger moves back and forth against the background of more-distant objects. The closer the finger is, the bigger the shift. And the same is true for a star. In this case, the shift indicates that the star is about 60 light-years away — making the shoulder of the centaur a fairly close neighbor.

Script by Damond Benningfield, Copyright 2014

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