In this exciting book Isaac Asimov, Professor of Biochemistry at Boston University and creator of some of the most original sicence fiction, turns his attention to science fact. He traces the development of man's observations about his own, and other, worlds, from the early theories of Hecataeus, Eratosthenes and Galileo to those of Max Planck, Hoyle and Gamow. With expert clarity he also unravels the complexities of modern astronomy, explaining just what is meant when astronomers refer to Quasars, Dark Nebulae, Receding Galaxies and other phenomena.