Also known as the Hercules cluster, M13 is
perhaps the finest and most well known globular cluster in the
Northern hemisphere. It originally was discovered by Edmond
Halley in 1714. Halley noted that the cluster could easily be
seen with the naked eye on dark, moonless nights. As its common
name would imply, M13 lies in the constellation Hercules. It is
about 25,000 light-years from us, and has an impressive diameter
of about 150 light-years.