 Kuhn’s historical work covered several topics in the history of physics and astronomy. During the 1950s his focus was primarily on the early theory of heat and the work of Sadi Carnot. However, his first book concerned the Copernican revolution in planetary astronomy (1957). This book grew out of the teaching he had done on James Conant’s General Education in Science curriculum at Harvard but also presaged some of the ideas of The Structure of Scientific Revolutions. In detailing the problems with the Ptolemaic system and Copernicus’ solution to them, Kuhn showed two things. First, he demonstrated that Aristotelian science was genuine science and that those working within that tradition, in particular those working on Ptolemaic astronomy, were engaged in an entirely reasonable and recognizably scientific project. Secondly, Kuhn showed that Copernicus was himself far more indebted to that tradition than had typically been recognized. Thus the popular view that Copernicus was a modern scientist who overthrew an unscientific and long-outmoded viewpoint is mistaken both by exaggerating the difference between Copernicus and the Ptolemaic astronomers and in underestimating the scientific credentials of work carried out before Copernicus. This mistaken view—a product of the distortion caused by our current state of knowledge—can be rectified only by seeing the activities of Copernicus and his predecessors in the light of the puzzles presented to them by tradition that they inevitably had to work with. While Kuhn does acknowledge the influence of causes outside science (such as a resurgence in Sun worship (1962/70a, 152–3)), he nonetheless emphasizes the fact that astronomers were responding primarily to problems raised within science. What appealed to them in Copernicus’ model was its ability to do away with ad hoc devices in Ptolemy’s system (such as the equant), to explain key phenomena in a pleasing fashion (the observed retrograde motion of the planets), and to explain away otherwise inexplicable coincidences in Ptolemy’s system (such as the alignment of the Sun and the centres of the epicycles of the inferior planets).