Timekeeping · a Light

Mosques put an astronomer on the payroll

The five prayers are defined by the sun: first light, the moment a stick's shadow reaches a set length, sunset. Working out when those moments fall on a given day at a given latitude is astronomy, and from the thirteenth century mosques in Egypt and Syria employed a salaried official to do it, the muwaqqit. He kept the tables, checked them against the sky, and set the times for the muezzin. The post drew serious people: Ibn al-Shatir held it in Damascus, and so did al-Khalili. Their everyday tool was the sine quadrant, a quarter circle of brass or wood with a plumb line and a grid of curves, on which the day's trigonometry could be read by sliding a bead along a thread.

The muwaqqit · Egypt and Syria, from the 1200s