Messier 13 (M13), also known as the Great Globular Cluster in Hercules, is a globular cluster located in
Hercules constellation. It is one of the brightest and best known globular clusters in the northern sky. The cluster has an apparent magnitude of 5.8 and lies at a distance of 22,200 light years, or 6,800 parsecs, from Earth. Its designation in the New General Catalogue is NGC 6205.
The Hercules Globular Cluster has an estimated age of 11.65 billion years and contains about 300,000 stars. The estimated mass of the cluster is about half a million solar masses.M13 stretches across 20 arc minutes of the sky, which corresponds to a linear diameter of 145 light years. The cluster can be seen without binoculars in exceptionally good viewing conditions, with clear skies and no light pollution.The brightest star in M13 is V11, a red giant classified as a Cepheid variable. V11 has a visual magnitude of 11.95 and lies approximately 25,100 light years from Earth.
The Hercules Globular Cluster contains an unusually young, B2-type star, designated Barnard 29. The star does not really belong to the cluster, but was presumably picked up by M13 on its orbit around the Milky Way. Other stars in the cluster are very old and only have about 5 percent of the Sun’s iron content as they were formed before the stars in our galaxy created metals. M13 also contains about 15 blue stragglers, old stars that appear younger and bluer than their neighbours.Messier 13 is a class V globular cluster, one with an intermediate concentration of stars toward the centre. It has a densely packed central region, with up to a hundred stars populating a cube only 3 light years on a side.
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