M23 - NGC 6494

Messier 23 (NGC 6494) is a large and attractive open cluster in the constellation Sagittarius, located approximately 2,150 light-years from Earth. The cluster contains roughly 150 stars spread across a diameter of about 15 light-years and shines at a combined apparent magnitude of about 6.9. M23 is estimated to be around 300 million years old, placing it in the intermediate age range for open clusters, old enough for its most massive stars to have evolved off the main sequence into red giants but young enough to retain a substantial population of bright blue-white stars. The cluster was discovered by Charles Messier on June 20, 1764, who described it as a cluster of stars closely packed together. M23 lies in a relatively uncrowded region of Sagittarius, about 5 degrees northwest of M24 (the Sagittarius Star Cloud), which makes it stand out more prominently than it might if it were embedded in the densest part of the Milky Way. Through binoculars, M23 appears as a bright, elongated haze with several individual stars beginning to resolve. A small telescope at low to moderate magnification provides an excellent view, revealing a rich and evenly distributed field of stars with subtle chains and arcs. The cluster spans about 27 arcminutes, nearly the diameter of the full Moon, so low magnification and wide fields of view show it best. M23 has been described by observers as having a particularly pleasing and balanced appearance, with no single dominant star but rather an even sprinkling of similarly bright members that give it a refined, uniform character.

Contains about 150 stars spanning 15 light-years at a distance of 2,150 light-years, with an estimated age of 300 million years.