Johannes Kepler. The Sun as the Heart of the World

In two early unpublished texts (a Disputation in favor of Copernicus of 1593 and the Apologia pro Tychone against Ursus of 1600), Kepler argued with the Pythagoreans that, contrary to Aristotle (De caelo, ii, 13), the geometrical center of the cosmos coincides with its natural center. Since the Sun is the body that occupies this central position, Kepler conceives it as the heart of the world and the principle of planetary motion. In the following study, we examine how Kepler further develops this pivotal theme in a letter to Herwart von Hohenburg of 25 March 1605 and later in the Dissertatio cum nuncio sidereo (Prague, 1610) as well as in a German translation and critical commentary of the Aristotelian chapter, which ultimately remained unpublished as well.