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Galactic Nests

July 22, 2012

Like a chick that’s left the nest, the Sun moves through the galaxy alone. But many of the galaxy’s stars are still in their nests — in great clusters of hundreds of stars. All the stars in a cluster are members of the same brood — they were all born from the same giant cloud of gas and dust.

Two examples are near the tail of Scorpius, which is low in the south at nightfall.

The brighter one is M7, which is to the left or upper left of the two stars that represent the scorpion’s stinger. Under moderately dark skies, it’s visible to the unaided eye as a tight knot of stars. Binoculars reveal more stars, and telescopes reveal still more.

From the types of stars the cluster contains, astronomers deduce that M7 is about 200 million years old — only about five percent the age of the Sun. That youthfulness is one reason the cluster is still together. As a cluster orbits the center of the Milky Way, the combined gravity of the galaxy’s other stars gently pulls it apart, sending its stars off on their own.

The other cluster, M6, is to the upper right of M7. It’s farther than M7, so it doesn’t look as big or bright. In fact, you need pretty dark skies to see it without optical aid. With optical aid, the colorful stars of M6 form a pattern that resembles the outline of a butterfly. M6 is also young, so its stars are also still tightly bound together by their own gravity — keeping the nest full for a little while longer.


Script by Damond Benningfield, Copyright 2012


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