This chapter takes its starting date as the eleventh century AD for several reasons. First, one can argue that it was in the eleventh century that Arabic astronomy was finally ‘acclimatized’ within the Islamic environment and from then on it began to be coloured with whatever prerequisites that environment demanded. From this perspective several works began to be characterized by original production, and were no longer mere repetitions of problems that were discussed in the Greek tradition. Figures such as Abū Sahl al-Kūhī, Abū al-Wafā’ al-Būzjānī, Bīrūnī, Manṣūr ibn Naṣr ibn ‛Irāq, etc., who lived just around the turn of the previous century, were setting the grounds for this new production in astronomical research. This work could still be considered as a continuation of that of Ḥabash al-Ḥāsib, Thābit Ibn Qurra, Khwārizmī and others of the previous ninth century.
Second, the eleventh century witnessed a series of works all characterized by a genuine interest in the philosophical basis of Greek astronomy. As a result, these works led to a new school of writers on astronomical subjects whose main concern was to point out the problems that were inherent in the Greek astronomical system. One should recall the works of Ibn al-Haytham in his Shukūk, Abū ‛Ubayd al-Jūzjānī in his Tarkīb al-Aflāk and the anonymous Spanish astronomer in his Istidrāk. The problems raised by these astronomers were later taken up by ‛Urḍī, Ṭūsī, Quṭb al-Dīn al-Shīrāzī and Ibn al-Shāṭir, among others. The last four astronomers have been referred to in the literature as the ‘School of Marāgha’, mainly because of the association of the first three with the observatory built by the Ilkhānid monarch Hūlāgū in the city of Marāgha in northwest modern Iran in AD 1259. If one were to take their works alone, one could show that within the thirteenth century, when the first three lived, there occurred a real revolution in astronomical research and a definite change in attitude towards astronomical presuppositions. This tradition, started in the eleventh