Moving in Step

Five of the stars of the Big Dipper are kindred spirits. They move through the Milky Way Galaxy together, and they may even share a birthplace. And they have some fellow travelers in other constellations.

Together, the stars form the Ursa Major Moving Group. It’s a stream of a few dozen stars. The most prominent are five members of Ursa Major, the great bear. They form all but the tip of the handle and the outer edge of the bowl of the Big Dipper, which makes up the bear’s body and tail.

The stars in the group move through the galaxy in the same direction, and at about the same speed. That suggests they’re roughly bound together by their gravitational pull — or they were in the past. And they’re all about the same age — a few hundred million years. For stars, that’s quite young.

The members of the group also have about the same chemical composition. That could mean they were born from the same cloud of gas and dust. But a study a couple of years ago noted that many other stars of the same age have a similar make-up. So while the stars of the Ursa Major Moving Group may be kindred spirits, they may not be actual kin.

Look for the Big Dipper low in the northern sky at nightfall this month, roughly parallel to the horizon. Some of the other members of the moving group are in the adjoining constellations Draco, which is above the dipper, and Boötes, to the left of the dipper.

We’ll have more about Ursa Major tomorrow.

Script by Damond Benningfield