Messier 3 is a fine large globular cluster in Canes Venatici. It is located 12 degrees northwest of Arcturus (Alpha Boötis) along a line straight to Cor Caroli (Alpha Canum Venaticorum).

M3 subtends an apparent angle of 18 arcminutes, and shines at magnitude 6.2, making it visible to the unaided eye of a keen-eyed observer from a true dark-sky observing site. It is estimated to be 8 billion years old.

At a distance of 34,000 light-years, its true size would be 178 light-years in diameter.

M3 is estimated to contain 500,000 stars, the brightest of which is magnitude 12.7. The 25 brightest stars have an average magnitude of 14.23.

More than 200 variable stars have also been discovered in M3, the most in any globular cluster. A number of Blue Stragglers have also been found. These are main sequence stars that appear to be younger than the rest of the stars in the cluster because of their blue color, but are now believed to be cluster members who have had their outer layers removed in close encounters with other stars while passing through the central dense region of the cluster.

M3 was discovered by Charles Messier on May 3, 1764. It was his first original discovery, but he logged it as a nebulous object not to be confused with a comet. William Herschel was the first to resolve the cluster into stars, with a larger telescope, in 1784.

North is to the right in the above image.

M3 Catalogs: M3, NGC 5272 Object Type: Globular Cluster Magnitude: 6.3v Size: 18.0' Constellation: Canes Venatici Image Field Centered At: RA: 13h 42m 12s Dec: +28° 22' 01"