Measuring Earth — From Shadows to Satellite Coordinates
Nine scenes connect shadows and coordinate tables at Alexandria, a mountain and the horizon at Nandana, a navigational map at Duisburg, triangulation in Tornio and India, error calculation at Göttingen, the prime-meridian agreement at Washington, and a GPS test satellite launched from Vandenberg. Rather than one person measuring Earth and turning it into a map, the route follows how local angles, baselines, clocks, and international conventions changed what “my position” could mean.
Scene 1 of 9
c. 240 BCE
Alexandria
Two Cities’ Shadows — Calculating a Circumference No One Could Walk
Eratosthenes combined the difference between solar angles at Alexandria and Syene near the summer solstice with an estimate of the distance between the cities. Parallel sunlight and the geometry of a sphere let a local angle stand in proportion to the whole circumference. His original work is lost and the method survives in a brief later account by Cleomedes, so the famous well, personal observations, hired pace counters, stadium conversion, and modern percentage accuracy should not be fused into one certain scene.
Replay on the map from scene 1Scene index