<ref>Dreyer, J. L. E. (1878). "A Supplement to Sir John Herschel's "General Catalogue of Nebulae and Clusters of Stars"</ref>
<ref>Bradt, H. (2004). Astronomy Methods: A Physical Approach to Astronomical Observations. Cambridge University Press. p. 52. ISBN 978-0-521-53551-9.</ref>
<ref>Corwin, H.G. Jr. (12 October 1999). "The NGC/IC Project: An Historical Perspective". The NGC/IC Project. Retrieved 2012-04-22.</ref>
<ref>Dreyer, J. L. E. (1895). "Index Catalogue of Nebulae found in the years 1888 to 1894, with Notes and Corrections to the New General Catalogue".</ref>
<ref>Erdmann, R. E. (2010). "The NGC/IC Project". The NGC/IC Project. Retrieved 2012-04-22.</ref>
<ref>Steinicke, W. (17 January 2012). "Revised New General Catalogue and Index Catalogue". Retrieved 2012-04-22.</ref>အချို့၏ နယူကလိများ
