On the Solar Model and the Precession of the Equinoxes in the Alphonsine Zīj and its Arabic Sources

Abstract

Alphonse X, King of Castille (1252-1284), sponsored astronomical work previous to the compilation of the Alphonsine Tables, carried out by his two Jewish collaborators Yehudah ben Mosheh and Isaac ben Sid. On the one hand, these tables can be considered the first European attempt to develop original research in astronomy, but on the other hand, an analysis of this work should be concerned, first of all, with its Islamic precedents. This is why I tend to consider the Alphonsine Tables as another zīj which should be studied in the light of what we know concerning the development of Islamic zījes in Medieval Spain. Of these, two seem to be well documented as having been known and used by the Alphonsine collaborators. One of them is al-Battānī’s zīj, the canons of which were translated into Spanish (Bossong, 1978), and which may have been used to compute the solar positions for the end of each month appearing in four Alphonsine works (Astrolabio redondo, Cuadrante para rectificer, Relogio dell agua, and Lámina Universal). These positions have been computed, however, with the Alphonsine Tables themselves. The second zīj known in the Alphonsine circle was al-Zarqalluh’s Toledan Tables, used — as O. Gingerich has established — to compute the solar and planetary positions in the horoscope which was cast to establish the propitious moment to start the Latin translation of Ibn Abī-l-Rijāl’s Kitāb al-bāric fī ahkām al-nujūm (Hilty, 1954, lxii-lxiii).