Qibla · a Light

A Damascus timekeeper computed the qibla for every latitude

Finding the direction of Makkah from anywhere else is a problem in spherical trigonometry, and Muslim astronomers knew it. In the fourteenth century Shams al-Din al-Khalili, the timekeeper at the Umayyad mosque in Damascus, computed a table of about 2,880 entries giving the qibla for every degree of latitude and every degree of longitude difference from Makkah. When David King checked the values against exact modern computation, almost all were correct to within a minute or two of arc. Ordinary travellers used simpler things: brass compass boxes made in Istanbul and Isfahan, with a needle, a list of cities and the angle to set for each. Early mosque qiblas vary, and surveyors are still measuring them.

Shams al-Din al-Khalili · Damascus, 14th century