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Leaving the Nest

April 30, 2016

Our solar system is heading into the aftermath of a stellar breakup — a stream of stars that split away from a big family of stars. One of the brightest members of the stream stands in the east at nightfall, and high overhead not long after midnight: Alphecca, the brightest star of Corona Borealis, the northern crown.

The stars in the stream once were members of a good-sized cluster. Today, though, the cluster’s been whittled down to only about a dozen stars, including five stars of the Big Dipper.

The cluster is being torn apart by the gravitational tug of other stars, plus giant clouds of gas and dust. Dozens of stars that once belonged to the cluster are now moving through the galaxy on their own, forming a stream that spans hundreds of light-years. The Sun is on the outskirts of the stream, but it’s moving in a different direction.

Astronomers are pretty sure of the origin of the stars in the stream because they still move in the same speed and direction as the cluster’s core. The stars are all about the same age, too, and they have the same chemical composition — good indications that they’re all members of the same stellar family.

Alphecca is 75 light-years away — about the same distance as the cluster’s core. It’s in a pretty semicircle of stars that’s about a third of the way up the eastern sky at sunset. Alphecca is at the center of the semicircle — a member of a big stellar family that’s heading off on its own.


Script by Damond Benningfield

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