The central position of the sun is the noteworthy innovation of Nicolas Copernicus (1473-1543). Technically, however, the system is not heliocentric: the momentary center of revolution, C, represents the center of earth’s orbit, not a gemetric or physical center. Two other innovations are also of interest. First, the use of a double epicycle for lunar motion, and second, the model for Mercury–which has the planet liberating on the center of an epicycle, rather than revolving around it. This simplified drawing is not intended to represent relative planetary destances or radial dimensions.