Cusa: Learned Ignorance (1440)

1. Cusa: Learned Ignorance (1440) • The earth, which cannot be the centre, must in some way be in motion; in fact; Just as the earth is not the centre of the world, so the circumference of the world is not the sphere of the fixed stars.

2. Cusa Continued you will recognize that the art of calculating lacks precision, since it presupposes that the motion of all the other planets can be measured by reference to the motion of the sun. Even the ordering of the heavens --with respect to whatever kind of place or with respect to the risings and settings of the constellations or to the elevation of a pole and to things having to do with these-- it is not precisely knowable. Since no two places agree precisely in time and setting, it is evident that judgments about the stars are, in their specificity, far from precise

3. Cusa Continued • It is now evident that this earth really moves though to us it seems stationary. In fact, it is only by reference to something fixed that we detect the movement of anything. How would a person know that a ship was in movement, if, from the ship in the middle of the river, the banks were invisible to him and he was ignorant of the fact that water flows? Therein we have the reason why every man, whether he be on earth, in the sun or on another planet, always has the impression that all other things are in movement whilst he himself is in a sort of immovable centre; he will certainly always choose poles which will vary accordingly as his place of existence is the sun, the earth, the moon, Mars, etc.

4. Copernicus

5. Copernican Model • The Copernican model places the sun at the center of the solar system and all the planets orbit about it. Most importantly, Copernicus endows movement to the Earth. In fact, three kinds of movement: • annual motion (orbit about the sun) • daily rotation (around a tilted axis) • axial wobble (changes the positions of fixed stars over thousands of years timescale)

6. Copernican Model The major difference in quality between the models of Aristarchus, Ptolemy and de Cusa was that Copernicus worked out his model in full mathematical detail but the resulting system/device was every bit as complicated as the Ptolemaic model.

7. Model Bias: • His model also has equally spaced circular orbits between the planets (in actuality this holds rather true for Mercury thru Mars). Equally space perfectly circular orbits again represents harmony and order in Nature. • He also uses the Aristotelian mechanism of a Prime Mover to account for the original motion

8. Copernicus Writes For it is only the circle which can bring back what is past and over with; and in this way, for example, the sun by a movement composed of circular movements brings back to us the inequality of days and nights and the four seasons of the year. Many movements are recognized in that movement, since it is impossible that a simple heavenly body should be moved irregularly by a single sphere.