1320?-1380?

Arab astronomer and mathematician who compiled an extensive series of tables necessary for Muslim prayer rituals. Working at the Umayyad Mosque in Damascus, al-Khalili was responsible for providing a means of timekeeping in order to regulate the hours of the five daily prayers that are a part of the Islamic faith. This required extensive knowledge of geometry, and his calculation of the exact direction of the Muslim holy city of Mecca—toward which all Muslims pray—forced him to confront challenging problems in spherical trigonometry.