Presented is book five in a series of six books in the University of Illinois Astronomy Program which introduces astronomy to upper elementary and junior high school students. This guidebook discusses the interior of stars, their source of energy, and their evolution. Topics presented include: the physical properties of the sun; model of the solar interior; using known physical laws as guides; the source of solar energy; properties of stars - their luminosities; temperatures; masses; stellar models; the evolution of stars; and birth and death of stars. (Author/DS)