Taking much-explored topics, Mr. Branley manages the usual range with ease: the known ""facts"" of our universe and galaxy; the historical dilemmas which have plagued sky watchers; the chronological history of great astronomers and their achievements relevant to galactic understanding. But he goes further: with the ease of a teacher, one very good at his trade, he leads the reader into the fascinating area of how we estimate some of our facts and in so doing presents more science than all of the ""facts"" taken together. The reader is introduced to the assumptions upon which total concepts are placed, often rather cautiously. He comes to realize that the great debates of science may arise from disputes about the validity of axioms rather than about the reliability of the data. Thus he will be able to appreciate such problems as the computation of stellar magnitudes, galactic distance, and the probable age of the milky way (including its likely future). The most serious recent competitor is Asimov's To the Ends of the Universe which, although attempting much more, covers some of the same ground and also does it well.