Olle Dellblad: Excentrisk och epicyklisk teori i Ptolemaios och Kopernikus

Abstract: Western astronomy before Kepler assumed that the celestial bodies moved in uniform, circular motion. In order to account for deviations from this ideal in the observed data, Ancient Greek astronomers developed mathematical 'hypotheses' such as eccentric circles and epicycles. This work provides an introduction to the theory of these hypotheses as originally formulated by Apollonius of Perga (c. 240-190 B.C.), then demonstrates their adaptation by Ptolemy and Copernicus for their respective solar and planetary models. This mathematical theory is then compared with the Newtonian formulation of Kepler's planetary laws in order to understand its strengths and weaknesses as an astronomical model.