ʾABŪ SAʿĪD AL-SIǦZĪ AND THE “STRUCTURE OF THE ORBS,” THE EARLIEST KNOWN WORK ON HAYʾA

Abstract

Abstract ʾAbū Saʿīd al-Siǧzī was a prominent fourth/tenth century astronomer and mathematician who was one of the first contributors to the new genre of ʿilm al-hayʾa (science of the configuration). However, little is known about the initial steps taken in the formation of the discipline, or its independence from other astronomical writings and practices. In this paper, I will discuss new findings about Siǧzī’s life to determine details of his biography and a more precise time period for his scientific activities. I then describe, for the first time, a composition in theoretical astronomy from the fourth/tenth century, the “Structure of the orbs” (Tarkīb al-aflāk) by Siǧzī to show its place in the formation of the discipline of ʿilm al-hayʾa, comparing Siǧzī’s book to the earlier work of al-Farġānī on the size of the earth and the number of celestial spheres. I conclude that Siǧzī’s Tarkīb al-aflāk is the earliest known example of a book that contains only topics found in later hayʾa and may be the first appearance of the ninth celestial orb that became standard in the later genre.