First, read Measuring the World by Slices and Sticks. Think about how a tiny shadow angle could reveal the size of the whole Earth. Eratosthenes used one slice of sunlight to understand the planet.
In this activity you use a small angle and a known distance to estimate Earth’s circumference. You are doing with shadows and circles what we will later do with areas and slopes: using simple local information to understand something big.
This Introductory adventure prepares you for motion, velocity, acceleration, exponentials, limits, derivatives, and the DiVA charts. Everything in the Adventures series grows out of these two ideas: area and slope.
Redraw the picture, re‑shade the region, or re‑estimate a slope. Your best tools are still triangles, rectangles, and your eyes.