The purpose of this book is twofold: to provide a brief, simple introduction to the theory of radiation and its applcation in astrophysics and to serve as a refernce manual for researchers. The first part of the book consists of a dicussion of the basic formulas and concepts that underlie the classical and quantum descriptions of radiation processes. The rest of the book is concerned with applications. The spirit of the discussion is to present simple derivations that will provide some insight into the basic physics involved and then to state the exact results in a form useful for...