Timekeeping (ʿilm al-mīqāt) was one of the applied astronomical disciplines from the Islamic period in which one deals with determination of the Muslim's prayer times using the shadow of sundial gnomons. According to the Islamic religious sources, such as ḥadīth and legal elaborations, ẓuhr and ʿaṣr praying times should be determined based on the shadow length of gnomon. Indeed the sundial has historically been used as an astronomical instrument by which determining the time based on the shadow length of gnomon is possible; as a matter of fact, in Islamic societies (particularly in Syria and Egypt) some institutions were formed in mosques which were dedicated to such activities officially and they used reckoning methods for this purpose. At the same time, the methods for making sundials were developed as well. Some Muwaqqits, (people who were expert in ʿilm al-mīqāt and worked for mosques), compiled major works which played important role in this evolution. It is noteworthy that these activities promoted some fields such as mathematical astronomy, particularly spherical trigonometry. Because of the importance of ʿilm al-mīqāt, it prevailed in Islamic territories very soon. This research provides a survey of the formation and development of timekeeping methods from the Islamic period (between 11th and 16th c. CE) and their roles in the development of sundial designs and constructions. It also comprises various traditions of timekeeping, the most important astronomers who contributed to this field, and their works. The transmission of timekeeping methods in Egypt, Syria, Yemen and Turkey is also discussed.
Keywords: Timekeeping, ʿIlm al-mīqāt, Prayer Time, Sundial, Gnomon, Muwaqqit.