M48
Messier 48 or M48, also known as NGC 2548, is an open cluster of stars in the constellation of Hydra. It was discovered by Charles Messier in 1771. There is no cluster in the position indicated by Messier. The value that he gave for the right ascension matches that of NGC 2548, however, his declination is off by five degrees. Credit for discovery is sometimes given instead to Caroline Herschel in 1783. Her nephew John Herschel described it as, "a superb cluster which fills the whole field; stars of 9th and 10th to the 13th magnitude – and none below, but the whole ground of the sky on which it stands is singularly dotted over with infinitely minute points". The brightest component is HIP 40348 at visual magnitude 8.3.
M48 is visible to the naked eye under good atmospheric conditions. It is located some 2,500 light-years from the Sun. The age estimated from isochrones is 400±100 Myr, while gyrochronology age estimate is 450±50 Myr – in good agreement. The cluster has a tidal radius of 63.3 ± 7.8 ly (19.4 ± 2.4 pc) with at least 438 members and a mass of 2,366 M☉. The general structure of the cluster is fragmented and lumpy, which may be due to interactions with the Galactic disk. The cluster is now subdivided into three groups, each of which has its own collective proper motion.
