The author's previous book includes titles on The Mysterious Earth and The Mysterious Sea. He is a past master of the art of bringing the technical down to a size that can be handled in conversational prose. The book is ideally organized to supplement high school level science courses introducing astronomy. The chapters move through space with sections devoted to meteorites, the moon, the sun, the Milky Way, etc. Synthesizing known information and speculating on the many unanswered questions that confront man's invasion of space, Mr. del Rey's tone is one of intelligent consideration and is without condescension. He does not forget to include the attention-holding material of bizarre experiments that border on the realm of science fiction, such as the possibility of life on Mars and beyond, as well as Project Ozma's record of radio signals from outer space. There is an excellent chapter on the contributions of photography to the study of astronomy and thumbnail sketches of the innovators and theoreticians in astronomy are included throughout the book.