Eppur si muovono : Galileo, sunspots and precession / Keith Hutchison.
Abstract:
This paper performs two closely connected tasks. It's rewiews, firstly, Topper's criticisms of earlier literature on Galileo's argument that the observed motion of sunspots supports Copernicanism. Topper correctly observed that this literature ignored Galileo's understanding of the precession of the equinoxes, and noted that precession requires precisely the same problematical motions as a geocentric accommodation of the sunspots. So Galileo's argument seems to depend on a sleight of hand, not picked up in the literature. I argue however, that it was reasonable for Galileo to ignore precession. Given this, I then construct a systematic review of Galileo's argument, showing that the superiority it detects in Copernicanism is not due to it relocation of the sun, but to the inertial mechanics applied by Galileo to his Copernican kinematics. If the same mechanics is applied to the motion of sunspots in a geocentric universe, then exactly the same simplicity is found as in the heliocentric universe. What makes sunspots difficult for scholastics, then, is not the geometry of their universe, but the dynamics they apply to it - AristotleĢs solid spheres
Galilaeana A. 10 (2013), p. 3-24