M75 - NGC 6864

Messier 75 (NGC 6864) is a globular cluster located approximately 67,500 light-years from Earth in the constellation Sagittarius, making it one of the most distant globular clusters in the Messier catalog. It was discovered by Pierre Mechain in 1780 and cataloged by Charles Messier later that year. M75 is a highly concentrated globular cluster with a Shapley-Sawyer class of I, the most concentrated classification, meaning its stars are extremely densely packed toward the center. The cluster spans about 130 light-years in physical diameter and is intrinsically very luminous, with an absolute magnitude of about -8.6, though its great distance means it appears relatively faint from Earth at visual magnitude 8.5. Despite being very distant, M75 is one of the most centrally concentrated of all Milky Way globular clusters, with a density so extreme in the core that individual stars become impossible to resolve even in the largest ground-based telescopes. The cluster contains an estimated several hundred thousand stars and has a relatively high metallicity for its location in the galactic halo. M75 has at least a few known variable stars, though it has not been as extensively studied as many closer globulars. In amateur telescopes, M75 appears as a small, bright, intensely concentrated ball of light that resists resolution into individual stars. Even telescopes of 10-12 inches show only a bright, unresolved core surrounded by a faint halo of nebulous light. The cluster's high concentration means it has a very star-like appearance at low magnifications, and it could easily be mistaken for a fuzzy star. M75 lies about 8 degrees southwest of the star Dabih (Beta Capricorni), in a relatively barren area of sky.

M75 spans about 130 light-years in diameter and lies approximately 67,500 light-years from Earth, making it one of the most distant Messier globulars.