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February 23, 2011

There's only one sun in our sky, but for many other worlds, that's not the case. Most of the stars in the galaxy are systems of two stars or more. So any planets orbiting these stars have more than one sun. And if anyone lives on these planets, their concepts of day and night might be quite different from our own.

Consider Dubhe, the star at the top right corner of the bowl of the Big Dipper. Although our eyes see only a single point of light, the system actually consists of at least four stars.

The stars form two close pairs. The more prominent pair includes the star that's visible to the unaided eye. It's a stellar giant -- it's much bigger and brighter than the Sun. It's also much cooler, so it looks orange. The companion star isn't as big or bright, but it's impressive nonetheless -- a hotter star that shines pure white.

These stars are a little closer together than the planet Neptune is to the Sun. So if any planets orbit either star, they'd experience a cycle of day and night quite unlike our own. Sometimes, they'd have two bright suns in the sky, sometimes just one, and sometimes none. There would be times of year when one sun would rise as the other sets, meaning there would be no night at all.

The other pair of stars in the system would be too far to shine as true suns. But they'd punctuate the sky as dazzling points of light, whirling around each other every six days -- adding to the drama of the skies day and night.


Script by Damond Benningfield


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