Although Coma Berenices is a small constellation it does contains one of the densest concentrations of external galaxies in the sky. However its most outstanding feature is not a galaxy but an extremely large and loose naked eye open cluster called Mel 111 or the Coma Star Cluster. In total, Mel 111 contains about 50 stars spread over 6 degrees of apparent size at a distance of 280 light-years.
Although conspicuous and easily visible to the naked eye the cluster was not included in both the Messier or NGC catalogues due to its loose nature, large apparent size and unproven status as a genuine open cluster. It was in 1938 that Swiss-American astronomer Robert J. Trumpler identified 37 stars as cluster members, establishing its true nature. Before that in 1915, British astronomer Philibert J. Melotte included it as number 111 in his catalogue of star clusters, hence the name Melotte 111 or Mel 111.
Mel 111 is located on the southern side of star gamma Com (γ Com - mag. +4.35). This star appears as a cluster member but seems to be a foreground star at 170 light-years distant. The group's brightest stars are all of 5th magnitude, including 12,13,14,16 and 21 Coma Berenices. The Coma Star Cluster is of the finest areas for scanning with binoculars with the brightest stars make out a distinctive "V" shape. With 7x50 models it fits nicely into the field of view (FoV) but with 10x50's it may even over-spill depending on the binocular's apparent FoV. Telescopically it doesn't show much due to their limited fields of view but for binocular observers, this is a gem of an open cluster.
Mel 111 is the second nearest open cluster to the Earth after the Hyades in Taurus (153 light-years). It's best seen from northern latitudes during the months of March, April and May.
Melotte 111 Data Table
|Name||Coma Star Cluster|
|Object Type||Open Cluster|
|RA (J2000)||12h 25m|
|DEC (J2000)||26d 0m|
|Apparent Size (degrees)||6 x 6|
|Number of Stars||50|
|Age (years)||450 Million|
|Notable Feature||One of the nearest star clusters|