From Copernicus to Descartes : the empyrean, the stellar parallax and the movement of the Earth

The Copernician revolution has comological consequences upon which Copernic has expressed little, and the scale of which will be measured only by Giordano Bruno or Descartes. The most spectacular aspect of this post-Copernician revolution is of course the suppression of the sphere of fixed stars. The present article examines this question through two perspectives : (i) that of an empyrean sky and (ii) the (vain) quest for a stellar parallax that for Kepler, Galileo and Descartes supposedly proved a posteriori Copernic's theory. We underscore finally the great subtlety of the argument layed out in Descartes' Principia Philosophiae (1644) that uses the arbitrary supposition of the empyrea to set the strictly geomobilistic copernicans against their tychonian adversaries who hoped via this supposition to maintain the Earth's immobility at the center of the World.