Late Medieval Planetary Theory

Abstract

THIS PAPER IS an attempt to describe and discuss models for representing planetary motion developed in the thirteenth century or shortly thereafter. A series of four articles which have appeared in this journal 1 have dealt with the related work of a Damascene astronomer of the following century, one Ibn al-Shatir. The latter gives a list of his predecessors who worked in the same field, and an effort has been made to examine systematically the extant writings of these individuals. The findings are of some general interest in the history of astronomy, but more particularly they supply partial material for an eventual solution of the problem of transmission posed by the existence of numerous identical elements between the work of Copernicus and that of Ibn al-Shatir. Hulagu, grandson of Genghis Khan, conqueror of Baghdad, and founder of the Mongol Il-khan dynasty of Iran, established an astronomical observatory at Maragha in Iranian Azerbaijan. The scientific activity there was under the leadership of Nasir al-Din al-Tusi (1201-1274),2 a savant of wide interests and varied activities whose work in planetary theory, as we shall see in Sections 3 and 4 below, supplied the impetus for the developments here described. Associated with him were a number of astronomers attracted from regions as widely separated as China on the East and Spain to the West. It will be convenient to refer to this group as the Maragha School. One member of the school mentioned by Ibn al-Shatir is Muhi al-Din al-Maghribi.3 He compiled a set of astronomical tables (a z[l) after the death of Nasir al-Din, but the theory underlying the computations seems to be Ptolemaic in character. The theory behind an earlier zij, which he