As painless a tour through the galaxies as you're likely to find, this starts out with a comfortable demonstration--hold a finger close to your face and look at it with first one eye closed, then the other--of the Greek discovery of ""parallax"" as a way of measuring distance. Soon we are looking out at the stars from a galaxy that is not round like a basketball but flattened like a hamburger patty, and observing the nova in the Andromeda nebula which prove that cloud to be another galaxy--the first of millions now detected and a possible hundred billion estimated. Introducing the time dimension, Asimov zips through a smoothly linked sequence from the Doppler-Fizeau effect to Hubble's constant, Einstein's explanation for Hubble's observation, and the correction of Einstein's early assumptions by Eddington and others. (""Einstein said afterward that inventing that figure was the worst mistake he had ever made."") Having thus glanced past Einstein, readers are ready for the Big Bang and the discovery of the radiation that Gamov predicted would confirm that theory. In closing--will there be a Big Crunch? is the universe open or closed?--Asimov plays up the fun of having still more to discover. ""It isn't quite that simple, of course,"" as he notes disarmingly after explaining how the periods of the variable stars called Cepheids provide ways to measure astronomical distances. But if the point is to make the distant galaxies accessible, here they are.