Moving Dipper

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The stars that make up most of the connect-the-dot patterns in the night sky appear close to each other just by coincidence. In most cases, they aren't related to each other, and their distances from Earth can vary by hundreds of light-years.

One exception is the most famous star pattern of all: the Big Dipper -- the brightest stars of Ursa Major, the great bear. Five of the seven stars that make up the dipper are part of a stellar family. The stars are all about the same distance away, and they're moving through space together.

The family is called the Ursa Major Moving Group.

All the stars in the group were born at about the same time, from the same cloud of gas and dust. They originally formed a tight cluster. Over time, though, the gravity of all the other stars in the galaxy pulled the cluster apart. Even so, the stars in the group continue to move through space in the same direction.

The five stars in the center of the Big Dipper form the center of the group. They're about 80 light-years away. Dozens of other group members are scattered across the sky.

The Big Dipper is high in the northeast at nightfall, standing on its handle. The star at the tip of the handle is about 20 light-years farther than the Ursa Major Moving Group, while the one at the outer tip of the bowl is about 20 light-years farther than that. These two stars go their own ways -- separate from the Big Dipper's big family.

Script by Damond Benningfield, Copyright 2008

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