Now in its 4th edition, this classic text presents a quantitative understanding of a range of astrophysical concepts. Emphasizing physical concepts, the book outlines cosmic events but does not portray them in detail. Instead, it provides a series of astrophysical sketches showing how to obtain quantitative insights into the structure and evolution of stars, the dynamics of cosmic gases, the large-scale behavior of the universe, and the origins of life. Nearly every part of the text has been reconsidered and rewritten for the new edition; new sections cover recent developments, and the remainder has been revised and brought up to date.