Islamic astronomy designates the astronomy of Islamic civilization, the civilization of regions where Islam was the religion of either the rulers or the majority of the populace. In observational activity, and often the patronage that supported it, were central to the enterprise of Islamic astronomy, people must quaint with the practical applications of astronomy. The astrolabe was the instrument suited to all of these applications of observational astronomy in timekeeping, astrology, and sacred geography. Traditionally, scholars have focused their attention on how translations of texts on astronomy from Greek, Sanskrit, and Pahlavi flourished under the Abbasid caliphs to establish an identity apart from those of their predecessors, the Umayyads. The need to correct parameters posed by the translations of the Almagest brought the first documented program of systematic astronomical observation. Ptolemy's planetary models relied on two devices, the eccentric and the epicycle, that were known as early as the time of Apollonius. The religious applications of observational astronomy remained prominent.