Describes the physics of a number of interesting situations in what used to be called deep space, at a level of mathematics and physics comprehensible to third-year undergraduate physics students. Discusses the interstellar medium and how information about it is obtained; the microscopic processes occurring and how they determine the properties of the gas; and the behavior of the gas with respect to macroscopic events such as interstellar grains, radiatively excited regions, and star forming. Includes problems with answers. Updated from the 1980 to keep up with developments in astrophysics. Annotation c. by Book News, Inc., Portland, Or.