Following Ptolemy, Greek astronomy rapidly declined and ended with the Arabian conquest of Alexandria in AD 641. Although the magnificent library and museum were destroyed, the Arabs encouraged learning and for the next 800 years developed an important astronomical tradition of their own. Observatories were established at a number of cities including Damascus, Cairo, Baghdad, and Meragha. One of the greatest stimuli to Arabian astronomy was the need to calculate and maintain the Islamic calendar, which demanded new mathematical methods and more precise timekeeping.
Among the greatest of Arabic astronomers were: