Although Coma Berenices is a small constellation it does contain one of the densest concentrations of galaxies in the sky. However, its most outstanding feature is not a galaxy but an extremely large and loose naked eye open cluster, called Melotte 111 or the Coma Star Cluster. In total, Melotte 111 contains about 50 stars spread over 6 degrees of apparent sky. It's located 280 light-years from Earth.

Although conspicuous and easily visible to the naked eye, the cluster was not included in either the Messier or NGC / IC catalogues. This was due to its loose nature, large apparent size and unproven status as a genuine open cluster. It was in 1938 when Swiss-American astronomer Robert J. Trumpler first identified 37 stars as members and therefore established its true nature. Before that in 1915, British astronomer Philibert J. Melotte included the object as number 111 in his catalogue of star clusters, hence the name Melotte 111 or Mel 111.

Melotte 111 The Coma Star Cluster imaged from the International Space Station (ISS) (credit:- Donald R. Pettit/NASA)

Finder Chart for Melotte 111 (credit:- freestarcharts)

Finder Chart for Melotte 111 - pdf format (credit:- freestarcharts)

Melotte 111 is located on the southern side of star gamma Comae Berenices (γ Com - mag. +4.35). This star appears to be a cluster member, but is actually 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 Comae Berenices. The Coma Star Cluster is of the finest regions of the sky for scanning with binoculars. The brightest stars making out a distinctive V shape. With 7x50 models it fits nicely into the field of view, but with 10x50's it may well over-spill. Telescopically it doesn't show much, but for binocular observers this is a gem of an open cluster.

Melotte 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

Melotte111
Collinder256
NameComa Star Cluster
Object TypeOpen Cluster
ConstellationComa Berenices
Distance (light-years)280
Apparent Mag.+1.8
RA (J2000)12h 25m
DEC (J2000)+26d 0m
Apparent Size (degrees)6 x 6
Radius (light-years)18
Number of Stars50
Age (years)450 Million
Notable FeatureOne of the nearest star clusters

Sky Highlights - April 2017

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