| Messier 48 | |
|---|---|
 Open cluster Messier 48 in Hydra | |
| Observation data (J2000epoch) | |
| Right ascension | 08h 13m 43.0s[1] |
| Declination | −05° 45′ 00″[1] |
| Distance | 2,500 ly (770 pc)[1] |
| Apparent magnitude (V) | 5.8[2][3] |
| Apparent dimensions (V) | 30′[2] |
| Physical characteristics | |
| Mass | 2,366+1,109 −755[4] M☉ |
| Radius | 63 ly[4] |
| Estimated age | 450±50 Myr[5] |
| Other designations | M48,NGC 2548,[6]Cr 179, H IV-22 |
| Associations | |
| Constellation | Hydra |
| See also:Open cluster,List of open clusters | |
Messier 48 orM48, also known asNGC 2548, is anopen cluster of stars in theequatorialconstellation ofHydra. It sits near Hydra's westernmost limit withMonoceros,[7] about 18° 34′ to the east and slightly south of Hydra's brightest star,Alphard.[8] This grouping was discovered byCharles Messier in 1771, but there is no cluster precisely where Messier indicated; he made an error, as he did with M47. The value that he gave for theright ascension matches, however, hisdeclination is off by five degrees.[9] Credit for discovery is sometimes given instead toCaroline Herschel in 1783.[9] Her nephewJohn 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".[8]
M48 is visible to thenaked eye under good atmospheric conditions. The brightest member is the star HIP 40348 at visual magnitude 8.3.[8] The cluster is located some 2,500 light-years from the Sun.[1] The age estimated fromisochrones is400±100 Myr, whilegyrochronology age estimate is450±50 Myr – in good agreement.[5] This makes it intermediate in age between thePleiades, at around 100 Myr, and theHyades, at about 650 Myr. Themetallicity of the cluster, based on the abundance of iron (Fe), is [Fe/H] =−0.063±0.007 dex, where −1 would be ten times lower than in the Sun. It is more metal-poor than the Pleiades, Hyades, andPraesepe clusters.[10]
The cluster has atidal radius of 63.3 ± 7.8 ly (19.4 ± 2.4 pc)[4] with at least 438[11] members and a mass of2,366 M☉.[4] The general structure of the cluster is fragmented and lumpy, which may be due to interactions with thegalactic disk. The cluster is now subdivided into three groups, each of which has its own collectiveproper motion.[11]
