The star cluster M7 shines brightly against the background of the Milky Way. The cluster is perhaps 1,000 light-years away and contains about 80 stars. Some of the stars are nearing the ends of their lives, so they have grown larger and brighter. They help make the cluster visible to the unaided eye, near the border between Scorpius and Sagittarius, although you need a dark sky to see it. [N.A.Sharp/REU program/NOAO/AURA/NSF]
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Most of the constellations are tough to pick out. Their classical "connect-the-dots" outlines are so faint, small, or spread out that it's tough to see them as a picture.
That's not the case for two of the most prominent constellations of summer, though. Scorpius and Sagittarius are big and bright, and they're easy to pick out. Tonight, they're in the south as night falls. Look for the curving body of the scorpion just above the horizon, with the orange star Antares in its middle. Sagittarius is to the left of the scorpion, with its brightest stars forming a teapot.
If you have a dark sky, away from city lights, look about halfway between them -- between the scorpion's stinger and the teapot's spout -- for a hazy patch of light that's a bit bigger than the full Moon.
That's M7, a star cluster that's close to a thousand light-years away. Its 80 stars all formed from the same cloud of interstellar gas and dust, sometime between 200 million and 300 million years ago.
One reason the cluster stands out is that several of its stars are nearing the ends of their lives, so they've puffed up to giant proportions. Such stars are hundreds of times brighter than the Sun, so they're visible across great distances.
Binoculars will reveal quite a few more of the cluster's stars, while a small telescope will let you see most of them -- a family of stars nestled between two prominent constellations of summer.
More about Scorpius tomorrow.
Script by Damond Benningfield, Copyright 2011