The claim that even in 1543 the Copernican theory was objectively superior to the Ptolemaic theory is explained and defended. The question is then raised concerning the relevance of this insight for our understanding of the rationality of the Copernican revolution. It is proposed that (a) the decision to reject the Ptolemaic theory first became clearly rational early in the 17th century as a result of Galileo's observations of the phases of Venus, and (b) the decision to accept the Copernican (...) theory only became clearly rational when Newtonian gravitational theory provided reasonable physical grounds for rejecting the Tychonic theory towards the end of the 17th century. (shrink)