Part 4, Chapter 1 (Galaxies) of the course lecture notes. The lecture notes were taken in the Fall of 2001 by Jeremy Schnittman, who as a student in the subject, agreed to take notes and to format them using LaTeX. He used Professor Paul Schechter’s handwritten notes in producing them. The figures were produced by Caitlin Millard during June-August 2004. Used with permission. As of the date of publication, only lecture notes for sessions 1 through 11 were available.