Reference

	The Collected Contributions of Fred L. Whipple. Volume II, The Space Age and Other Writings by Fred L. Whipple Year: 1972 Hits: 3762 Date insert: Monday, 31 December 2018
	The Constellations: An Enthusiasts Guide To The Night Sky by Lloyd Motz, Carol Nathanson Year: 1998 Hits: 4091 Date insert: Monday, 31 December 2018
	The Finest Deep Sky Objects by Wallace McCall, James Mullaney Year: 1966 Hits: 3925 Date insert: Monday, 31 December 2018
	The International Encyclopedia of Astronomy by Ernest H. Cherrington, Sanner NA Year: 1987 Hits: 9893 Date insert: Monday, 31 December 2018
	The Joy of Gazing: A Personal Guide for the New Observer by Dale C. Ferguson, Kip S Thorne Hits: 1898 Date insert: Monday, 31 December 2018