The book was written in the 1950s, so the discussion of science and technology is out of date. It is interesting to see how science has changed and predictions have changed. Regardless, the author is insightful and knowledgeable about astrophysics. I was surprised to see the ideas on terraforming of Venus. He is optimistic about the advancement of space flight and planetary colonization. I found this an interesting book and suggest it for creative concepts for space exploration. ( )