Eratosthenes Measures the Earth

Two sticks, one shadow, and the size of the planet, 2,200 years before satellites.

Around 240 BC the librarian of Alexandria measured the circumference of the Earth with a shadow and some geometry. Move the sticks yourself and see how close he got.

Steps

1. The Librarian
2. Everyone Knew It Was Round
3. The Well at Syene
4. Two Sticks, One Shadow
5. Doing the Math
6. What It Started