Third Chpater of Kūshyār's Zīj and Farghānī's Jawāmi Ilm al-Nujūm: a Comparison between Two Predecessors of Hayʾa Works and Their Importance in hayʾa Books

Hayʾa works is a general name for the astronomical works which provide a geometrical description of the configuration of the world. Most of this kind of astronomical works were written by Islamic scholars probably under the influence of Ptolemy’s Planetary Hypotheses. Most of Islamic hayʾa works have a similar structure and order of chpters and have been written in 6AH/12AD century. Nevertheless, we have some astronomical works in 3-4AH/9-10AD centuries which have some similarities with the hayʾa works so that we can call them the “predecessors of hayʾa works”. Al-Farghānī’s Jawāmiʿ Ilm al-Nujūm and the third chpter of Kūshyār’s al-Zīj al-Jāmiʿ are two important works among these predecessors. Concidering the four chpter organization for Hayʾa works, i.e. mathematical and physical introduction, configuration of the heavens, mathematical geograpgy and masses and distances (Abʿād wa Ajrām), we compare in this article these two treatises with each other and other hayʾa works. This article claims that the third chapter of Kūshyār’s al-Zīj al-Jāmiʿ is more similar to the next Hayʾa works and probably it is more impressive.