Qibla · a Light

He tabulated the direction of Makkah for every latitude

Facing Makkah from anywhere else on earth is a problem in spherical trigonometry. You need the shortest path over a sphere between two points whose latitudes and longitudes you know, and then the angle that path makes with north. Exact solutions were worked out in the ninth century, and al-Biruni wrote a whole book on pinning down the coordinates that go into them. In the fourteenth century Shams al-Din al-Khalili, timekeeper at the Umayyad Mosque in Damascus, computed the answer in advance for every combination of latitude and longitude difference across the inhabited world, close to three thousand entries, by hand. When his table was checked against modern computation in the twentieth century, almost every entry proved correct.

Al-Khalili · Damascus, fourteenth century