Ibn al-Shāṭir and Copernicus: The Uppsala Notes Revisited

Abstract

It has long been recognized that Copernicus’ models in the Commentariolus bear a striking resemblance to those of Ibn al-Shāṭir (14th-c. Damascus). A number of scholars have postulated some sort of transmission but have denied that Ibn al-Shāṭir’s geocentric models had anything to do with the heliocentric turn. Rather, the assumption has been that they were used by Copernicus solely to resolve the irregular motions of the planetary deferents brought on by Ptolemy’s equant. Based on proposals for direct transformations of Ibn al-Shāṭir’s models into those of Copernicus and an alternative reading of Copernicus’ so-called Uppsala notes, it is argued here that Ibn al-Shāṭir’s models in fact have a “heliocentric bias” that made them particularly suitable as a basis for the heliocentric and “quasi-homocentric” models found in the Commentariolus.