Track the constellation Hercules as it wheels highs across the summer sky. Although not bright, it has a distinctive shape and can be easily picked out with a little effort.
The chart shows Hercules at midnight on 2 July, high in the south-western sky. To identify it, locate two bright stars: orange Arcturus in Boötes and, much higher, blue-white Vega in Lyra. Look from one to the other and your line of sight passes through the body of Hercules, marked by four fainter stars. This off-kilter square is known as the keystone.
A great star cluster is visible partway between two of the stars in the keystone. Catalogued as M13, it contains more than 300,000 stars yet is so far away that it is only just visible to the naked eye as a smudge under excellent viewing conditions.
Hercules, named after the Roman hero of myth, was one of Ptolemy’s original 88 constellations.
