Degree of difficulty 2 (of 5)

Minimum aperture Naked eye

Designation NGC 2548

Type Open cluster

Class I3r

Distance 2510 ly (K2005) 2540 ly (CMD, 2005) 2510 ly (proper motion, 2002)

Size 22 ly

Constellation Hydra

R.A. 8h 13.8min

Decl. –5° 45′

Magnitude 5.8

Surface brightness –

Apparent diameter 30′

Discoverer Messier, 1771

History M 48 was discovered by Charles Messier on the 19th of February 1771. He describes this object as a “cluster of very faint stars without nebulosity.” As with M 47 that same night, he made a mistake in his calculation of the coordinates and ended up 5° north of the true position. Hence, M 48 was considered one of the lost Messier objects, and the cluster was known only as NGC 2548 – until in 1959 T.F. Morris pointed out its identity as Messier's missing object.

Hence, Johann Elert Bode made an independent discovery of this star cluster in 1782. In his small star atlas, we find this object in its true place, as well as “Messier 48” in its wrong position, 5° north. Another independent discovery of M 48 was made by William Herschel's sister Caroline in 1783. She saw “a beautiful cluster of very compressed stars, pretty rich, 10' or 12' diameter.”

50 years later, Smyth wrote about M 48: “A splendid group, in a rich splashy region of stragglers, which fills the field of view, and has several small pairs, chiefly of the 9 th magnitude.” Around the same time, John Herschel praised a “a superb cluster which fills the whole field; stars of 9 th 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.”

Lord Rosse believed the cluster been “riddled with dark lanes and openings,” while Mädler counted about 100 stars and wrote: “without distinct boundaries, so that some stars lie far out. In the denser part there is a nice double star.”