Everyone has learnt something about the modern picture of the universe – its vast, unimaginable distance, its lifelessness, its indifference  to and aloofness from mankind – so completely different from the primitive picture in which mankind is the centre and everything around, beneath and above him ministers to his needs. How has this enormous change in our outlook come about? What is the nature of the evidence for the modern view? These question must have occurred to every – one at some time or other and many of the popular books on astronomy fail to answer them. All too often they merely present the conclusions and the reader is expected to accept them unquestioningly.