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Messier 13

Globular Cluster M13 (NGC 6205), class V, in Hercules

Hercules Globular Cluster

Right Ascension 16 : 41.7 (h:m)
Declination +36 : 28 (deg:m)
Distance 25.1 (kly)
Visual Brightness 5.8 (mag)
Apparent Dimension 20.0 (arc min)

Discovered by Edmond Halley in 1714.

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 (Arp 1955). The membership of this star was confirmed by radial velocity measurement, and is strange for such an old cluster - Glyn Jones suspected that it may be a captured field star. However, it was found that this star is actually an evolved star, probably a genuine cluster member, which has burnt up its nuclear fuel and lost most of its outer layers, a so-called post-AGB (post asymptotic giant branch) star (Conlon 1993, Conlon et.al. 1994). It is probable that this star is just in process to develop a planetary nebula, so that future astronomers may be able to observe such a rare object in famous M13. More info on M13 Barnard 29.

Observers note 4 apparently star-poor regions in M13 (e.g., Mallas). Suggestions of them can be noted in some photos.

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, e.g., in the DSSM image. This galaxy has recently produced a type II supernova (SN 2004A).

  • Historical Observations and Descriptions of M13
  • More images of M13
  • Amateur images of M13, more amateur images
  • More info on M13 Barnard 29
  • Study of the Variables of M13 by F. Violat Bordonau

  • Multispectral Image Collection of M13, SIRTF Multiwavelength Messier Museum
  • Marco Castellani's data for M 13
  • Christine Clement's Catalog of Variable Stars in M13
  • SIMBAD Data of M13
  • NED Data of M13
  • Publications on M13 (NASA ADS)
  • Observing Reports for M13 (IAAC Netastrocatalog)
  • NGC Online data for M13


    Hartmut Frommert
    Christine Kronberg

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    Last Modification: January 10, 2021