Zeta UMa Observatory

M13 - Hercules Globular Cluster

M13 (NGC 6205) fue descubierto por Edmond Halley en 1714. Se trata de uno de los cumulos globulares más destacados y conocidos del hemisferio norte. Su diámetro angular de 20 minutos de arco, se corresponde con un diametro "real" de 145 años luz. Contiene más de 100,000 estrellas. En su centro las estrellas se encuentran 500 veces más concentradas que en las cercanías del sol. Este cúmulo fue elegido en 1974 como uno de los blancos para el envío de mensajes para posible vida extraterrestre desde el radio-telescopio de Arecibo, debido a su concentracion tan elevada de estrellas. A unos 40 minutos de arco al noreste, se puede encontrar una débil galaxia, NGC 6207, en la que hace poco se ha descubierto una supernova del tipo II (SN 2004A). Messier 13 (M13, NGC 6205), 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 Charles Messier, who cataloged it on June 1, 1764, it is also reported in John Bevis' "English" Celestial Atlas. At its distance of 25,100 light years, its angular diameter of 20' corresponds to a linear 145 light years - visually, it is perhaps 13' large. 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 billion years (taken from Kenneth Glyn Jones). According to Kenneth Glyn Jones, M13 is peculiar in containing one young blue star, Barnard No. 29, of spectral type B2. The membership of this star was confirmed by radial velocity measurement, and is strange for such an old cluster - apparently it is a captured field star. Globular cluster M13 was selected in 1974 as target for one of the first radio messages addressed to possible extra-terrestrial intelligent races, and sent by the big radio telescope of the Arecibo Observatory. Nearby, about 40 arc minutes north-east of M13, is the faint (mag 11) galaxy NGC 6207, visible in many large- and medium-size-field photographs of M13. This galaxy has recently produced a type II supernova (SN 2004A). Taken from SEDS.
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