The Globular Cluster M3 in Canes Venatici. M3 is a beautiful cluster similar to the great Hercules cluster M13 and one of the 3 brightest clusters in the northern sky. The cluster is 35,000 light years away and 220 light years in diameter. It is estimated that M3 contains 500,000 stars and has a total mass 140,000 that of the Sun.