M68 - NGC 4590

Messier 68 (NGC 4590) is a globular cluster located approximately 33,600 light-years from Earth in the constellation Hydra. It was discovered by Charles Messier in 1780 and is a moderately concentrated cluster with a Shapley-Sawyer class of X, indicating a relatively loose structure. M68 spans about 106 light-years in physical diameter and contains an estimated 100,000 stars. The cluster is notable for being one of the most metal-poor globular clusters in the Messier catalog, with a metallicity of about [Fe/H] = -2.2, meaning its stars contain roughly 1/150th the iron content of the Sun. This extreme metal deficiency indicates that M68 formed very early in the history of the universe, when the interstellar medium had been minimally enriched by stellar nucleosynthesis. The cluster's age is estimated at approximately 11.2 billion years. M68 contains at least 42 known variable stars, including 28 RR Lyrae variables, which have been important for distance measurements and for studying the properties of these pulsating stars in a very metal-poor environment. The cluster also shows evidence of mass segregation, with more massive stars concentrated toward the center, and has an extended tidal tail suggesting ongoing tidal stripping by the Milky Way's gravitational field. For amateur observers, M68 lies in a relatively sparse region of the sky about 3.5 degrees southeast of the star Beta Corvi. In binoculars it appears as a small, faint fuzzy patch. A 6-inch telescope begins to resolve the outer stars, while 8-inch and larger instruments show a well-resolved cluster with a moderately concentrated core.

M68 spans about 106 light-years in diameter, contains roughly 100,000 stars, and lies approximately 33,600 light-years from Earth.