Gemma

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Summer is still officially more than a month away, but one of its signature stars is already putting on a good show. The star is Vega, in the constellation Lyra, the harp. It's one of the brightest stars in the entire sky, and forms one point of the Summer Triangle.

As Vega climbs the northeastern sky this evening, look to its upper right for a star that's just like it, but fainter and farther away.

The star is Gemma. Although it's not as dazzling as Vega, it's still easy to see because it's the brightest star in Corona Borealis, the northern crown -- a tight little pattern of seven stars that forms a semicircle.

Like Vega, Gemma is a white star that's a few dozen times brighter than the Sun. It's 75 light-years away -- exactly three times the distance to Vega.

Unlike Vega, though, Gemma has a companion star, which is a lot like the Sun. It's so close to Gemma that it completes an orbit around it every two and a half weeks. When the companion passes in front of or behind the main star, the system gets a tiny bit fainter.

The Gemma system was born along with five of the stars of the Big Dipper, which hangs high overhead early tonight. Those five stars are about as far from us as Gemma is. All of them were born about a half billion years ago, from a single giant cloud of gas and dust. The stars still move through space together -- a remnant of their common birth.

Script by Ken Croswell, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.