Eratosthenes’ Experiment: How Ancient Greeks Measured Earth’s Circumference #1730399 (License: Personal Use)

This diagram visualizes Eratosthenes’ famous 3rd-century BCE experiment: measuring the angle of the sun’s rays (7°12′ or 1/50th of a circle) between Syene (where the sun was directly overhead) and Alexandria (where a shadow formed), then using the known distance between cities to compute Earth’s circumference. The red dotted lines represent the angular difference, while yellow rays show parallel sunlight illuminating the spherical Earth.

Used in educational content about ancient astronomy, geometry, or STEM history-typically on science museum websites, school lesson pages, or articles explaining foundational scientific reasoning. Matches user intent to learn how early scientists estimated planetary dimensions using simple observations.