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February 20, 2016

Pollux is one of the brightest stars in the night sky — and one of the closest. The best measurement to date says the brighter of Gemini’s “twins” is less than 34 light-years away. Only a few hundred stars are closer, and few of those are especially bright. Even so, there’s a bit of uncertainty in exactly how far away Pollux really is — a matter of about 500 billion miles.

Astronomers measure the distances to nearby stars with a technique called parallax. They compare the star’s location against other stars when Earth is on opposite sides of the Sun. That tiny shift is like looking at a nearby object with first one eye, then the other — it shifts back and forth a bit against the background of more-distant objects.

The distance to Pollux was measured with an orbiting satellite. Above Earth’s blurring atmosphere, it saw the stars as crisp pinpoints instead of fuzzy blobs, improving its view. It found a distance of 33.78 light-years. But the uncertainty in that measurement is almost a tenth of a light-year — about half a trillion miles. It’ll take a much more precise measurement for future starship navigators to reach this bright stellar neighbor.

Look for Pollux high above the Moon this evening, with its “twin,” Castor, close by. Two other bright stars surround the Moon. The “little dog” star, Procyon, stands to the upper right of the Moon, with Regulus, the heart of the lion, to the lower left of the Moon. More about the Moon and Regulus tomorrow.

Script by Damond Benningfield, Copyright 2015

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