This booklet is the third in a series of nine that discuss the Apollo-Soyuz mission and experiments. This set is designed as a curriculum supplement for secondary and college teachers, supervisors, curriculum specialists, textbook writers, and the general public. These booklets provide sources of ideas, examples of the scientific method, references to standard textbooks, and descriptions of space experiments. There are numerous illustrations, as well as questions for discussion (with answers) and a glossary of terms. The series has been reviewed by selected high school and college teachers nationwide. This booklet is concerned with the layers in the sun, stars and gas clouds in the Milky Way, and the amount of helium in space. (MA)