ABSTRACT
Sometime early in the ninth century a certain astrologer known as Bizīst son of Fīrūzān read and interpreted the horoscope of one Māzyār, prince of Ṭabaristān under the overlordship of the Abbasid Caliph. Māzyār’s domain just south of the Caspian was part of a region which had successfully resisted the Arab invaders long after the rest of Iran succumbed, and it remained a centre of Iranian culture after its eventual penetration by Islam. Sometime before 830, Bizist turned Muslim, Arabized his Persian name into Yaḥyā bin Manṣūr (usually in the literature bin Abī Manṣūr), and became a nadīm (boon companion) of the Caliph al-Ma’ mūn. In fact, he founded a sort of dynasty of boon companions, a son, two grandsons, and a great-grandson following the same calling. To historians of science he is known as an astronomer, having participated in the work of the Abbasid observations at Baghdad and Damascus. He wrote a famous zīj, an astronomical handbook extant in a single corrupt copy, Escorial MS Ar. 927. This document is of great interest as being one of the few surviving examples of the earliest Islamic astronomy. However, it is also a frustrating book, for some portions of it are the work of later scientists, sometimes interpolated without indication of authorship 1 .
