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