VÉNUS SELON IBN AL-ŠĀṬIR
AbstractWe attempt to grasp the mathematics behind the planetary theories of the Syrian astronomer Ibn al-Šāṭir (1304–1375) in his treatise Nihāyat al-Sūl. Following the astronomers of the Marāgha school, by composing circular movements with constant angular velocity, Ibn al-Šāṭir attains two goals. He eliminates the need of excentrics and equant points in astronomy; but he also describes longitudes and latitudes with a unique method, with no more orbs than what is strictly necessary for the longitudes. A better understanding of rotation as a spatial transformation enables this ultimate economy of thought. In our commentary, we take Venus as an example offering an interesting problem about the latitudes. This is an opportunity to give a critical edition of the chapter of the Nihāyat al-Sūl dedicated to the latitudes of Mercury and Venus.