L'Abrégé de l'Almagested'Averroès, conservé uniquement en traduction hébraïque, reste inédit et peu étudié. Cet article a pour but de le faire connaître. Après avoir retracé l'histoire de l'Abrégé: date de rédaction, traduction, transmission de cette traduction, diffusion et audience, nous procédons à une première étude du texte: aperçu commenté du contenu, identification des sources et examen de leur exploitation critique par Averroès. Nous donnons également une traduction d'extraits significatifs du Prologue de l'Abrégé, avec une brève analyse. Avec l'Abrégé, nous disposons (...) d'un témoignage direct et relativement précoce, dû à l'un des plus importants artisans du mouvement de contestation et de réforme de l'astronomie ptoléméenne, animé au XIIe siécle par des penseurs andalous, philosophes aristotéliciens pour la plupart. (shrink)

This paper analyses a kinematic model for the solar motion by Quṭb al-Dīn al-Shīrāzī, a thirteenth-century Iranian astronomer at the Marāgha observatory in northwestern Iran. The purpose of this model is to account for the continuous decrease of the obliquity of the ecliptic and the solar eccentricity since the time of Ptolemy. Shīrāzī puts forward different versions of the model in his three major cosmographical works. In the final version, in his Tuḥfa, the mean ecliptic is defined by an eccentric (...) of fixed mean eccentricity and a mean obliquity fixed with respect to the celestial equator, and the center of the epicycle, which is inclined to the eccentric, moves on the eccentric with an annual period. By an additional slow motion of the sun on the epicycle, the true eccentricity of the solar deferent, defined by the annual motion of the sun, and the sun’s extreme declination from the equator change, accounting for the reduction of the eccentricity and the obliquity of the ecliptic since the time of Ptolemy. (shrink)

Representations of the heavens in various levels of detail can be found in a number of branches of Arabic literature. One particular genre, the hay'a texts, has as its purpose a full though non-mathematical discussion of the arrangement of the celestial orbs; hay'a writers are particularly sensitive to the philosophical requirements which all systems must meet. The pivotal work in this genre, On the Configuration, was written by Ibn al-Haytham. Later writers continued to produce works in the spirit of On (...) the Configuration. In the east, al-Tusi and his followers developed new models; in the west, a group of thinkers tried to rediscover the models which, so they thought, were the ones endorsed by Aristotle himself. (shrink)