References
^ Kenneth Glyn Jones (1991). 9780521370790, Cambridge University Press. Wiki. ISBN 9780521370790 (revised Dec 2013)^ Kenneth G. JonesPractical Astronomy Handbooks: Messier's Nebulae and Star Clusters 2 by Kenneth G. Jones (1991, Hardcover, Revised) ISBN 9780521370790 (revised Oct 2016)
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