Mr. Pickering, astronomer-emeritus of the Hayden Planetarium, teacher and television educator, presents an imaginatively conceived, lucidly written account of ""how telescopes and radio have enabled astronomers to map the heavens,"" and even more--the relation of the refinement of instruments to the growth of astronomical knowledge generally. He begins by recreating the fragmented conceptions of primitive man and his ancient descendants, the first complete picture held (with some dissension) from Ptolemy to Copernicus, and the contributions from Copernicus to Galileo. Then the first window, telescopic astronomy, opens, gradually widening the view with ""larger and larger telescopes, more accurate auxiliary instruments, improved photographic equipment and techniques."" When the knowledge available from the visible spectrum has been revealed, Mr. Pickering passes on to the second window, radio astronomy, the study of the electromagnetic spectrum. He concludes with teamwork between the two and a look outside the window via mechanical substitutes for man in outer space. His integration of personality, technology and theory gives the book a broad base of interest; his smooth, relaxed style and precisely evocative language and imagery easily sustain that interest.