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Object description
Messier 23 - an open star cluster in the constellation Sagittarius

Object description:

Messier 23 (NGC 6494) is one of the brighter open star clusters in the constellation Sagittarius. It lies at a distance of 2200 light-years from the solar system, about halfway to the Sagittarius Arm of our Milky Way. Only a few degrees east lies the center of the Milky Way. With a total brightness of the 5.5th magnitude class, it is visible to the naked eye under dark skies.
It contains about 150 stars starting with the 10th magnitude class. The apparent size in the sky covers just under 27 arcminutes, about the size of a full moon seen with the naked eye. This gives a physical diameter of 15 to 20 light-years for a distance of 2200 light-years. The star cluster has an estimated age of 300 million years and it is assigned to class III 1 m according to Trumpler.

The star cluster was discovered June 24, 1764 by Charles Messier.

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