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Messier Clusters

July 25, 2014

One of the first items on almost any amateur astronomer’s “to-do” list is completing the Messier marathon — looking at all 110 objects cataloged by Charles Messier. Messier himself began the first marathon 250 years ago.

Charles Messier ca. 1770Charles Messier ca. 1770Messier was most interested in finding comets. Indeed, the French astronomer discovered one in January of 1764. Not long afterward, though, he discovered something that looked like a comet but wasn’t. Today, we know that it’s a globular cluster — a tight grouping of ancient stars. All Messier knew, though, was that it was in the way of his comet hunting.

So he set out to compile a catalog of similar comet-like objects. He’d already logged a couple, although he found that they’d already been discovered by others. But the globular cluster had never been recorded by anyone — it was Messier’s first discovery of a deep-sky object.

During the summer of 1764, he scanned the skies in and around Sagittarius. The constellation is in the southeast at nightfall, with its brightest stars forming the outline of a teapot.

Among Messier’s discoveries in Sagittarius are a pair of young star clusters known as M21 and M25, and another globular cluster, M22. All three stand above the teapot, and are visible through binoculars.

By the end of 1764, Messier’s catalog listed 40 objects — putting him more than a third of the way through the first Messier marathon.

We’ll talk about another Sagittarius cluster tomorrow.


Script by Damond Benningfield, Copyright 2014

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