An open cluster of about eighty stars that lies in the far west of the vast constellation of Hydra, close to its border with Monoceros. With a visual magnitude of +5.8, the cluster is visible to the naked eye, but only under ideal conditions, though it is clearly visible with binoculars. It is most easily found by following an imaginary line through the two bright stars of Canis Minor, Gomeisa and Procyon: the cluster lies to the southeast of these two stars, at about three times their distance from one another.
The clustered stars of M48 occupy a region a little over twenty light years across. Estimates of its distance from the Sun vary, but most agree on a value of some 2,500 light years, lying outward across the disc of the Milky Way and somewhat outside the Galactic plane.
This cluster was lost for more than a century. When Charles Messier first catalogued it in 1771 he entered a mistaken value for its declination, and for many decades afterward it could not be located with certainty. It was not until 1934, 163 years later, that the object Messier intended for his catalogue number 48 was positively identified as the open cluster otherwise known as NGC 2548.