Messier 9 — Globular Cluster in Ophiuchus

M9 is a globular cluster in the constellation Ophiuchus, located about 25,800 light-years from Earth. It is one of the nearer globular clusters to the galactic center, lying only about 5,500 light-years from it. The cluster contains roughly 250,000 stars and spans about 90 light-years in diameter. Its apparent diameter is about 12 arcminutes. M9 appears slightly fainter and smaller than many other Messier globulars due to significant interstellar dust absorption along the line of sight toward the galactic center.

Located about 3.5 degrees southeast of Eta Ophiuchi. At magnitude 8.4, it requires binoculars to see as a small, faint fuzzy spot. A 4-inch telescope shows a round, unresolved glow with a brighter center. Apertures of 8 inches or more begin to resolve the outer edges into individual stars at 150x or higher. Two smaller globular clusters, NGC 6356 and NGC 6342, lie nearby for comparison. Best observed from June through August.

Discovered by Charles Messier on May 28, 1764. He described it as a 'nebula without stars.' William Herschel was the first to partially resolve it into stars. The Hubble Space Telescope imaged M9 in 2012, revealing its stellar population down to stars far fainter than the Sun.