The Coma Berenices Star Cluster, Melotte 111

This large and conspicuous cluster was first cataloged by Ptolemy; it is scattered

over an area of about 4.5 degrees diameter. Although conspicuous, it was neither

included in Messier’s nor in the NGC catalog, because its nature as a true,

physical cluster was proven only by R.J. Trumpler who identified 37 stars as true

cluster members.

The Coma star cluster is currently neither approaching nor receding from us, i.e.

it moves tangentially to us with a velocity directed to position angle PA=218 deg,

visible as a proper motion of 0.02 arc seconds per year. So member stars are

easily identified by having this proper motion and no Doppler shift in their

spectra. Its distance has recently been refined by data of ESA’s astrometric

satellite Hipparcos, and is now estimated at 288 light years (previous estimate

was 260).

The Sky Catalog 2000 gives an age of 400 million years, and the brightest star as

of apparent magnitude 4.35, the hottest spectral type of A0.

Our image was obtained by amateur

Last Modification: 25 May 1999, 16:35 MET