Messier 68 — Globular Cluster in Hydra

M68 (NGC 4590) is a globular cluster in the constellation Hydra, located approximately 33,600 light-years from Earth. At magnitude 7.8, it spans about 11 arcminutes, corresponding to a true diameter of roughly 106 light-years. M68 is classified as concentration class X on the Shapley-Sawyer scale, making it one of the more loosely concentrated globular clusters. It contains an estimated 100,000 stars. The cluster is relatively metal-poor with a metallicity of about [Fe/H] = -2.23, indicating that its stars formed from primordial gas with very few heavy elements — placing it among the most metal-poor globulars in the Milky Way. M68 contains 42 known variable stars, mostly RR Lyrae type pulsating variables, which serve as important distance indicators. The cluster is located well south of the ecliptic and relatively isolated on the sky, making it a somewhat overlooked object compared to the rich globular clusters in Ophiuchus and Sagittarius. M68 lies about 33,000 light-years from the galactic center, placing it in the outer halo of the Milky Way.

Located in the relatively star-poor region of Hydra, about 3.5 degrees south-southeast of Beta Corvi (Kraz) in the neighboring constellation Corvus. The sparse surrounding star field makes M68 somewhat challenging to find by star-hopping. Binoculars show it as a small, round, faintly glowing spot. A 4-inch telescope at 100x reveals a grainy, partially resolved halo around a brighter core. An 8-inch telescope at 150-200x resolves many individual stars across the cluster face, with chains and arcs of stars becoming visible in the outer regions. The relatively loose concentration makes resolution easier than with many other globulars. Best observed from March through June, though from northern latitudes it remains fairly low in the sky.

Discovered by Charles Messier on April 9, 1780. William Herschel was the first to resolve it into individual stars, describing it in 1786 as a beautiful cluster of stars. The cluster's low metallicity was established through spectroscopic studies in the 20th century, contributing to our understanding of the earliest epoch of star formation in the Milky Way's halo.