Mssier 3 (also known as M3 or NGC 5272) is a globular cluster in the constellation Canes Venatici. It was discovered by Charles Messier in 1764, and resolved into stars by William Herschel around 1784. This cluster is one of the largest and brightest, and is made up of around 500,000 stars. It is located at a distance of about 33,900 light-years away from Earth. M3 has an apparent magnitude of 6.2, making it visible to the naked eye under dark conditions.

While M3 is visible to the naked eye only under very good conditions and stays just below the limit of visibility under more average conditions, it can be easily seen with the smallest instrument. In binoculars, it appears just like a hazy, nebulous patch. A 4-inch shows its bright compact core within a round and mottled, grainy glow, which fades slowly and uniformly to the outer edges; it doesn't resolve the cluster, but shows just some of the brightest stars under good conditions. A 6-inch resolves the about outer two thirds into faint stars on a background glow formed by the unresolved fainter member stars of the cluster. An 8-inch shows stars throughout the cluster but in the very core, which is resolved into stars by larger telescopes (about 12-inch).