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William E. Harris: A Catalog of Parameters for Globular Clusters in the Milky Way. In: The Astronomical Journal. 1996. DOI10.1086/118116. Dostupné online.
MURDIN, Paul. Encyclopedia of Astronomy and Astrophysics. [s.l.]: Institute of Physics Publishing, 2001. Dostupné online. Kapitola M15. (anglicky)
O'MEARA, Stephen James. Deep Sky Companions: The Messier Objects. New York: Cambridge University Press, 1998. Dostupné online. ISBN0-521-55332-6. (anglicky)
HARRIS, W. E. A Catalog of Parameters for Globular Clusters in the Milky Way. S.1487. Astronomical Journal [online]. Říjen 1996 [cit. 2018-09-12]. Roč. 112, s. 1487. Dostupné online. doi:10.1086/118116. Bibcode1996AJ....112.1487H. (anglicky)
William E. Harris: A Catalog of Parameters for Globular Clusters in the Milky Way. In: The Astronomical Journal. 1996. DOI10.1086/118116. Dostupné online.
Laura Ferrarese, Maarten Baes, Patrick Cote, Roberto De Propris: G2C2 – I. Homogeneous photometry for Galactic globular clusters in SDSS passbands. In: Monthly Notices of the Royal Astronomical Society. 16.listopadu 2013. DOI10.1093/MNRAS/STT2002.
HARRIS, W. E. A Catalog of Parameters for Globular Clusters in the Milky Way. S.1487. Astronomical Journal [online]. Říjen 1996 [cit. 2018-09-12]. Roč. 112, s. 1487. Dostupné online. doi:10.1086/118116. Bibcode1996AJ....112.1487H. (anglicky)