Levi ben Gershom's Criticism of Ptolemy's Astronomy

Abstract

Levi ben Gershom or Gersonides (1288-1344), one of the most original thinkers of the Middle Ages, devoted the first section of the fifth book of his Milhamot ha-Shem to an exposition of his astronomical system, which was based on his own observations and departed in many respects from prevailing views. Heir to a long tradition of criticism of Ptolemy, which he associated notably with al-Bitrūjī Book on the Configuration [of the World], but which reached him also through Maimonides' Guide and Averroes' Epitome of the Almagest, Gersonides tried to reconcile the physical and the mathematical descriptions of the heavenly motions and provide a true picture of the configuration of the world. The long chapters 43 and 44 of his Astronomy are devoted, respectively to the demonstration that neither Ptolemy's nor al-Bitrūjī's astronomical theories can be true. Critical editions of the Hebrew and Latin versions of chapter 43 are presented here, along with an annotated English translation.