Harmonization of Calendars in the Early Islamic World as Reflected in al-Farghānī's Elements of Astronomy

This paper seeks to shed more light on calendrical knowledge in the first centuries of the Islamic era in which different administrative traditions fell under the control of a central government. Astronomy as a court-sponsored discipline in the Abbasid dynasty (132-656 AH/750-1258 CE), undertook the pivotal task of identifying and mastering various calendrical disciplines under the reign of the caliphs to make a centralized management feasible. In the first two centuries, the domination of the Arabic lunar calendar, whose significance lies in governing the Islamic yearly festivals and occasions, led to drastic disagreements with the annual planting cycles that were followed by the farmers. Accordingly, the official taxation system faced serious problems. The solution to which was the development of a well-established solar calendar. The large concern of the ninth-century Muslim astronomers for calendrical computations, acknowledges their integral participation in this executive challenge. The present study follows these practices through the lens of a ninth-century Arabic astronomical text, written by Aḥmad b. Muḥammad b. Kathīr al-Farghānī (Alfraganus in the west), known mainly as the Elements of Astronomy. The careful exploration of this text helps us achieve a broader image of time-keeping accounts in the early Islamic era and the need for calendrical conversions. Moreover, the author’s detailed report of the five existing calendars of the time (Arabic, Syriac, Byzantine, Persian and Egyptian) and their systems of nomenclature, opens an early window to the linguistic investigation of time-reckoning in the Islamic world.