YA?Q?B IBN T??RIQ

(fl. Baghdad, second half of eighth century),

astronomy

Ya ?q?b ibn T?riq was the astronomer most closely connected with al–F?zar?in introducing the Z?j al–Sindhind to Islamic scientists; he seems, in fact, to have collaborated personally with the Indian astronomer who came to Baghdad with an embassy from Sind in 771 or 773. The most important of his works in this connection were Z?j mahl?l f? al–Sindhind li daraja daraja “Astronomical Tables in the Sindhind Resolved for Every Degree” Tark?ib al–afl?ak “Composition of the Spheres” and Kit?b al–?ilal (Boos of Causes”).

Evidently the most prominent feature of the Z?j was that the interval between the entries in the columns of arguments for the tables was one degree. Its basic parameters were very similar to those of the Z?j al–Sindhind al–kab?r of al–Faz?r?, except that Ya’qub completely accepted the equations of the center from the Zij al–Shah while mixing in some equations of the anomaly from the Zij al–Arkand (the ardharatrika system; see essay in Supplement).

In the Tark?b al–afl?ck Ya?qub also drew upon the Z?j al–Sindhind and the Z?j al– Arkand, as well as on his conversations with the Indian astronomer. The subjects covered in this work, insofar as they can be determined, were the geocentric distances of the planetary orbits, geography, the computation of the ahargana and perhaps the geometric models of planetary motion. The Kit?b al?ilal is known only from citations by al–B?r?un? in his work On Shadows the extant fragments deal exclusively with rules for employing the gnomon. Like al–Faz?ar?, Ya ?q?b is inconsistent, adopting whatever formula comes to hand without regard for its relation to the other formulas in his books. Also like al–Faz?r?, he is significant primarily for his role in the transmission of Indian science to Islam.

BIBLIOGRAPHY

The fragments by Ya’qub ibn Tariq are collected and discussed in D. Pingree, “The Fragments of the Works of Yaqub ibn Tariq,” in Journal of Near Eastern Studies27 (1968), 97–125; and in E. S. Kennedy, “The Lunar Visibility Theory of Ya’qub ibn Tariq,” ibid 126–132

David Pingree