A large, regular cluster of more than 3000 galaxies, about 280 million l.y. away in Coma Berenices; also known as Abell 1656. It covers more than 4° of sky and has a true diameter of at least 20 million l.y. Most of the bright members are ellipticals or lenticulars. Two very bright giant ellipticals, NGC 4874 and NGC 4889, lie either side of the centre; these galaxies have about 1011 solar luminosities. The total mass of the cluster is estimated at 2 × 1015 solar masses.