M 23 (open cluster)

The cluster was discovered by Charles Messier on June 20, 1764 .

M 23 is at a distance of 2150 light years from Earth. Its diameter is 15-20 light years. In the cluster identified about 150 stars. The brightest have a magnitude of 9.2 ^m .

This open cluster in the northwest of Sagittarius belongs to summer objects. Observations from temperate latitudes of the northern hemisphere are complicated by the low position of the cluster above the horizon. But even in a relatively small telescope, a cluster is easily resolved with about fifty stars, of which 5-6 are quite bright. A fan-shaped pattern of star chains with a moderate magnification (50 times or more) fills the entire field of view of the eyepiece. In the dark southern sky, this is one of the richest in summer star clusters.

Using M 23 as a guide, one can find in two degrees southeast of a pair of the globular cluster NGC 6440 and the planetary nebula NGC 6445 "Little Gem" ("Little Gem") visible in the same field of view of the telescope. Such couples are quite rare.

Neighbors in the sky from Messier's catalog

• M 24 (a little to the east) - a separately hanging cloud of the Milky Way;
• M 25 (still further to the east) is another open cluster composed of brighter stars, but not so rich;
• M 21 , M 20 and M 8 (to the south) - a group of clusters that are not as bright and rich as M23, and a pair of nebulae: “Threefold” and “Lagoons”;
• M 18 , M 17 and M 16 (to the northeast, closer to the Shield) - a nondescript open cluster and another pair of bright nebulae: “Omega” and “Eagle”;
• M 9 (to the west, already in Ophiuchus) - globular cluster.

The sequence of observation in the Messier Marathon

... M 18 → M 24 → M 23 → M 25 → M 8 ...

• List of Messier Objects
• New Shared Directory

• Messier 23, SEDS Messier pages (English)