Messier 13


Messier 13 is a large globular star cluster about 25,000 light years from Earth. It contains several hundred thousand stars and is about 145 light-years in diameter. July is a good month to look for it with a pair of binoculars. About a-third of the way from Vega to Arcturus, four bright stars in the constellation of Hercules form the Keystone asterism. M13 can be seen partway between Zeta Herculis and Eta Herculis, the two star that form the shoulders of the constellation.

Image Credit: NASA / ESA