UNTIL THE 16th century the earth was said to be the center of the universe because Pythagoras said so. In the sixth century BC, he claimed that the sun and moon and indeed all the planets orbited around the earth in perfect circles, and this idea dominated astronomy for the next 2000 years. Copernicus, monk, doctor, and amateur astronomer, was born in Poland amid the stir of the Renaissance. The quickening of the human spirit that occurred at this time was accompanied by questioning of long-held theories. Men felt they were living on the brink of a new and modern age, an age marked not only by splendid achievement in art and architecture but also by the beginning of a revolution in science. Encouraged by the new sense of inquiry that was about, Copernicus began to read all that the Greeks had written about planetary motion, and he came to