Hercules Globular Cluster |Right Ascension||16 : 41.7 (h:m)
|Declination||+36 : 28 (deg:m) |Visual Brightness||5.8 (mag)
|Apparent Dimension||16.6 (arc min) Discovered by Edmond Halley
in 1714. M13, also called the `Great globular cluster in
Hercules', is one of the most prominent and best known globulars
of the Northern celestial hemisphere. It was discovered by
Edmond Halley in 1714, who noted that `it shows itself to the
naked eye when the sky is serene and the Moon absent.' According
to Messier it is also reported in John Bevis' "English"
Celestial Atlas. At its distance of 25,100 light years, its
angular diameter of 23' corresponds to 165 light years. It
contains several 100,000 stars; Timothy Ferris in his book
Galaxies even says "more than a million". Towards its center,
stars are about 500 times more concentrated than in the solar
neighborhood. The age of M13 has been determined by Sandage as
24 billion years and by Arp as 17 billion years around 1960; Arp
later (in 1962) revised his value to 14 billi