William E. Harris: A catalog of parameters for globular clusters in the Milky Way. In: The Astronomical Journal. 1996. DOI10.1086/118116. Dostupné online.
Sangmo Sohn, Ricardo P. Schiavon, Emanuele Dalessandro, Francesco R. Ferraro: Ultraviolet properties of Galactic globular clusters with GALEX. II. Integrated colors. In: The Astronomical Journal. 24. září 2012. DOI10.1088/0004-6256/144/5/126.
Lee Spitler, Duncan A Forbes: Uniting old stellar systems: from globular clusters to giant ellipticals. In: Monthly Notices of the Royal Astronomical Society. 2008. DOI10.1111/J.1365-2966.2008.13739.X.
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.
dx.doi.org
HARRIS, W. E. A Catalog of Parameters for Globular Clusters in the Milky Way. S. 1487. Astronomical Journal [online]. Říjen 1996 [cit. 2018-04-10]. Roč. 112, s. 1487. Dostupné online. DOI10.1086/118116. Bibcode1996AJ....112.1487H. (anglicky)
HARRIS, W. E. A Catalog of Parameters for Globular Clusters in the Milky Way. S. 1487. Astronomical Journal [online]. Říjen 1996 [cit. 2018-04-10]. Roč. 112, s. 1487. Dostupné online. DOI10.1086/118116. Bibcode1996AJ....112.1487H. (anglicky)
MELOTTE, P. J. A Catalogue of Star Clusters shown on Franklin-Adams Chart Plates. S. 175. Memoirs of the Royal Astronomical Society [online]. 1915 [cit. 2018-04-10]. Roč. 60, s. 175. Dostupné online. Bibcode1915MmRAS..60..175M. (anglicky)
vizier.cfa.harvard.edu
HARRIS, W. E. A Catalog of Parameters for Globular Clusters in the Milky Way. S. 1487. Astronomical Journal [online]. Říjen 1996 [cit. 2018-04-10]. Roč. 112, s. 1487. Dostupné online. DOI10.1086/118116. Bibcode1996AJ....112.1487H. (anglicky)
seds.org
messier.seds.org
FROMMERT, Hartmut. SEDS Messier Objects Database: Messier 68 [online]. [cit. 2018-04-10]. Dostupné online. (anglicky)
u-strasbg.fr
cdsads.u-strasbg.fr
William E. Harris: A catalog of parameters for globular clusters in the Milky Way. In: The Astronomical Journal. 1996. DOI10.1086/118116. Dostupné online.
simbad.u-strasbg.fr
SIMBAD Astronomical Database: Results for M 68 [online]. [cit. 2018-04-10]. Dostupné online. (anglicky)