Heart, Center of the World, and the Principle of Motion: from Aristotle to Kepler and Galileo

This article examines the transformation of the “heart of the world” concept and its influence on the understanding of what causes planetary motion. It begins with Aristotle’s conception of the sphere of the fixed stars and that of commentators such as Simplicius, Averroes, and Aquinas. The focus then shifts to the notion of a mobile Sun positioned between the upper and lower planets in the geocentric tradition of Macrobius, medieval, and Renaissance thinkers. We then examine the transition to the Copernican Sun, which is both stationary in terms of its central geometric position but also perceived as the “natural” or vital center of the universe. These ideas are then traced from Copernicus and Rheticus to Kepler and Galileo. We will conclude with some considerations concerning Giordano Bruno and William Harvey, and the intriguing connection between the circulation of the blood and the Sun’s role as the heart of the world.