carried the so-called fxed stars, which always stay in the same positions relative to eachother bue which rotate together across the sky. What lay beyond the last sphere was never made very clear, bat it certainly was not part of mankind's observable universe. Prolemy’s model provided a reasonably accurate system for predicting the postions of heavenly bodies inthe sky. Bu in order to predict these postions correctly, Ptolemy had to make an as sumption that ehe moon followed path chat sometimes brought it twice as close tothe earth as at other times. And that meant that the moon ought sometimes to appear twice as big asa ater times! Prolemy recognized this law, but nevertheless his model was gen- cally, although not universally, accepted. It was adopted by the ‘Christian church asthe picture ofthe universe ‘dance with Seriprre, fr it had the great advantage that ‘of room outside the sphere of fixed stars for heaven and hell ‘Asimpler mode, however, was proposed in 1514 by a Polis priest, Nicholas Copernicus. (At first, perhaps for fear of bet branded a heretic by his church, Copernicus circulated his model