Object Analysis

Messier 39 (M39) is a large, loose open cluster in the constellation Cygnus. It was discovered by Charles Messier in 1764. Located about 800 light-years away, it is one of the closer open clusters to our Solar System. Because it is so close, it appears quite large on the sky—occupying an area nearly the size of the full moon.

M39 is an intermediate-age cluster, estimated to be between 200 and 300 million years old. It contains about 30 confirmed members, most of which are bright, blue-white stars. Unlike younger clusters that are still embedded in nebulosity, M39 has already cleared away its birth clouds of gas and dust, leaving the stars clearly visible against the dark sky.

Because the stars are so widely scattered, M39 is actually best viewed with binoculars or a very wide-field telescope at low magnification. It appears as a triangular grouping of bright stars. It serves as a great example of the "middle-age" phase of a cluster's life, before the stars eventually drift too far apart to be recognized as a group.