Type:		Book, Chapter
Title:		Universe, Chapter 16 (8th Edition)
Author(s):		Freedman, R. A.; Kaufmann, W. J.
Date:		2008
Publisher:		W. H. Freeman & Company
Start Page:		414
End Page:		428
Link:		http://www.ualberta.ca/~pogosyan/teaching/ASTRO_122/lect9/lecture9.html
Link (full):		http://bcs.whfreeman.com/universe8e/default.asp