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Moving Groups

October 11, 2016

You can’t see it, but the stars of the Milky Way are in constant motion as they circle through the galaxy. Most, including the Sun, do so alone. But many others do it in groups. Some groups are tightly bound clusters. The stars in other groups are more loosely scattered around. These wide-spread collections are known as moving groups.

The best known is the Ursa Major Moving Group, which was discovered in 1869 by British astronomer Richard Proctor. It’s centered in Ursa Major, the Great Bear, and it includes five of the seven stars of the Big Dipper.

These stars, plus several others in Ursa Major, are all about the same distance from Earth, and they’re all moving at the same speed and in the same direction. Their chemistry is similar as well, and they’re all the same age. That suggests that the stars were born together, then spread out over time.

The group isn’t limited to the stars of Ursa Major, though. It appears to include dozens of stars in many constellations, including Orion, Aquarius, Taurus, and Draco. Yet even though they’re widely dispersed, they share the same characteristics as the stars in Ursa Major.

There are other moving groups as well. One is centered in the southern constellation Doradus, for example, and another on the star Beta Pictoris. And several others have been discovered in just the last few years. They show that many of the stars that twinkle in the night still move through the galaxy with their siblings.


Script by Damond Benningfield

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