Great Globular Cluster in Hercules
Less than half way from Arcturus to Vega, four bright stars in the constellation of Hercules form the Keystone. M13 can be seen in the middle of Zeta Herculis and Eta Herculis. Only telescopes with a great light-gathering capability can best show the Hercules Globular Cluster. M13 is not clearly visible to the naked eye. With a low-power telescope, the Messier 13 looks like a comet. The cluster can be seen all year long, on some nights more than others. However, in the months of August and September it brightens the sky for a longer period of time.
scension 16h 41.7m and declination +36° 28'. With an apparent magnitude of 5.8, it is barely visible with the naked eye on a very clear night. Its diameter is about 23 arc minutes and it is readily viewable in small telescopes. Nearby is NGC 6207, a 12th magnitude edge-on galaxy that lies 28 arc minutes directly north east. A small galaxy, IC 4617, lies halfway between NGC 6207 and M13, north-northeast of the large globular cluster's center.