Eratosthenes Shadow Lab

Recreate the ancient shadow argument: two locations, same moment, different Sun angles. The angle difference maps to a fraction of Earth’s circumference.

Use shadow angles

Location A solar elevation angleLocation B solar elevation angleDistance between locations along north/south line (km)

Result

Angle difference

7.2°

Estimated circumference

40,000 km

Why this matters

The geometry does not require rockets, satellites, or photographs. It only requires simultaneous shadows, distance, and the willingness to let a prediction be checked.