The Celestial Spheres in the Writings of Greek and Arab Authors

Abstract

The notion of “celestial sphere” (Greek: sphaīra; Arabic: falak al-aflāk or “sphere of the spheres”) penetrates inside the spiritual universe of medieval Islam as a constituent part of the treatises of mathematics and astronomical physics written by Abū Al-‘Abbas Ahmad Ibn Muhammad Ibn Kathīr Al-Farghānī (IXth century), Abū ’Abdillah Muhammad Al-Battānī (ca. 858-929) and Abū ’Alī Muhammad Ibn Al-Hasan Ibn Al-Haytham (d. 1038) on the foundation of the celestial physics conceived by ’Aristotéles (384-322 B.C.) in Peri kósmon or De caelo and Klaúdios Ptolemaĩos (ca. 90-168
A.D.) in Mathematiké súntaxis, He Megále Súntaxis, He Megíste or Almagesta, as well as Hypotheses planetarium. Approached from a mathematical perspective, the spheres were conceived as ideal circles which represented the movement of the celestial bodies, and the system of the homocentric spheres was organized around the Centre of the Earth.