ABSTRACT
Until now the Mumtaḥan Zīj by Yaḥyā ibn Abī Manṣūr, one of the earliest extant Islamic astronomical handbooks with tables, 1 has been known only from a single manuscript of a late recension. Yaḥyā’s zīj was based on the results of the observational program carried out in Baghdad on the order of the Abbasid caliph al-Maʾmūn during the years AD 828–829. It consists of a mixture of materials of Indian and Iranian origin and the first systematic attempts to calculate Ptolemaic tables for planetary motions and spherical astronomical quantities on the basis of updated values for the underlying parameters. What has been thought to be the only surviving copy of the Mumtaḥan Zīj is contained in MS Escorial árabe 927. It is not complete, and is supplemented by texts and tables of a later date, for instance by Abū’l-Wafāʾ (Baghdad, second half of the tenth century) and Kūshyār ibn Labbān (Iran, ca. 1000). One of the most important objectives of previous research on the Escorial manuscript, in particular by Vernet, Kennedy and Viladrich, has been to distinguish between the original material stemming from Yaḥyā and later additions.
