Messier 13 or M13, also known as Hercules Cluster, is a bright globular cluster in the constellation Hercules. It is the brightest globular cluster in the northern sky, is about 25,100 light years away from the Sun, has 300,000 times the luminosity of the Sun and a diameter of 150 light years.
M13 has an apparent brightness of 5.8 mag. It can already be perceived as a nebulous spot by binoculars. In a telescope with an aperture of about 10 cm it can be resolved into single stars at the edge and is therefore a rewarding object for amateur astronomers. One finds it – best in spring or summer – at the “right square side” of Hercules, between the stars η and ξ Herculis.
Picture: Frank Bohlscheid, member of the STScI. Text: Wikipedia.
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