Messier 75 — Globular Cluster in Sagittarius

M75 is a highly concentrated globular cluster located about 67,500 light-years from Earth in the constellation Sagittarius, making it one of the most distant globular clusters in the Messier catalog. It shines at magnitude 8.5 and spans about 130 light-years in true diameter, though its apparent size is only about 6.8 arcminutes due to its great distance. M75 has a concentration class I, placing it among the most densely packed globular clusters known — its stars are extremely tightly compressed toward the center, making it very difficult to resolve individual stars even in large amateur telescopes. The cluster is estimated to be about 13 billion years old, among the oldest objects in the Milky Way.

Located in eastern Sagittarius, about 8 degrees south-southwest of the star Delta Capricorni. In binoculars, M75 appears as a small, fuzzy star. A 4-inch telescope shows a compact, bright core surrounded by a faint halo, but resolving individual stars requires at least a 10-inch telescope due to the cluster's extreme concentration and distance. Even in large apertures, the core remains an intense, unresolved blaze. The cluster is best observed at moderate to high magnification (150-200x) to reveal the granular edges. Best observed from July through September when Sagittarius is highest.

Discovered by Pierre Mechain on August 27, 1780, and cataloged by Messier on October 18 of the same year. Messier described it as 'a nebula without a star, between Sagittarius and the head of Capricornus.' William Herschel was the first to partially resolve it into stars in the late 18th century, noting its extreme condensation. The cluster's great distance places it on the far side of the Milky Way's center, roughly 47,600 light-years from the galactic core.