informal"" here means that Willy Ley has introduced much off-beat and fascinating information from the history of astronomy into a broad survey of historical developments in this basic science. Following a chronological path at the start, he later adopts a stimulating topical approach, both of which reveal what a startling amount of research, and no doubt enjoyment, went into putting this book together. All basic facts are here plus quite a bit of biographical information about many astronomers, as well as fairly complete discussions of well-known and not so well-known astronomical arguments. There the author gets too concerned with technicalities, they can be skipped, but they are there for those who want to know and are capable of understanding more. One weakness the failure to include some discussion of the steady-state and expanding universe theories. Ley feels they are too much with us and in too unsettled a state to include in a ""history"". But history is always being made, and a cross-section at any time tells where we are along the way. The topic is important in relation to the phrase ""space "" mentioned in the sub-title--and since we may be on the threshold of the demise of the steady-state theory.