Moving Dipper

The Big Dipper is on the move. Not just its nightly circle around the North Star. And not even its shifting position from month to month. The stars themselves are moving through the Milky Way Galaxy. And most of them are moving together.

The stars of the Big Dipper are in Ursa Major, the great bear. The constellation has given its name to a widely spread group of stars that appear to move together — the Ursa Major Moving Group. It consists of a few dozen stars in all. Its core is in Ursa Major, but it also includes stars in several other constellations.

The stars in the group all move through space in the same direction, at about the same speed. They’re all roughly the same distance from Earth — about 80 light-years. They all appear to be about the same age — roughly half a billion years. And they have similar chemical compositions. That doesn’t mean that all the suspected members really do belong to the group. But there’s a lot of circumstantial evidence that they do.

Members of the group may have been born together — from the same giant cloud of gas and dust. The gravity of the rest of the galaxy pulled them away from each other — leaving a long ribbon of stars that move through the galaxy together.

The Big Dipper is in the northeast at nightfall, with the handle below the bowl. Only two of its stars are not members of the Ursa Major Moving Group: the stars at the end of the handle and the outer edge of the bowl.

Script by Damond Benningfield