Why was astrology so important to the authors of the Rasā’il Ikhwān al-Ṣafā’?

De Callatay, Godefroid [UCL]

The Rasā’il Ikhwān al-Ṣafā’ include three epistles entirely devoted to ‘the science of the stars’ (‘ilm al-nujūm) – that is, epistles 3 (‘on astronomy’), 16 (‘on the heavens and the world’), and 36 (‘on cycles and revolutions’) –, in addition to countless other passages disseminated throughout the corpus. By reviewing this material, the present contribution will aim at elucidating why the authors of this unique encyclopedia made such an important use of ‘ilm al-nujūm, especially in terms of its astrological implications for the sublunary world and its inhabitants. The paper will focus on certain theories in particular, such as the Great Year doctrine, the theory of Saturn-Jupiter conjunctions, and the 7,000-year cycles of prophethood, with the purpose of determining to which extent the authors could combine these theories with their own messianic expectations.