This volume complements the author's highly successful Astrophysical Techniques (1991). It describes those characteristics of stars, groups of stars, and the material between the stars, which can be directly observed or inferred from the study of electromagnetic emissions or, occasionally, high energy particles. The complete text is suitable for most advanced undergraduate courses in astrophysics. However, the descriptive chapters are accessible to any scientifically literate non-specialist, and contain a wealth of material which will be of interest and use to a wide range of readers.