Eratosthenes of Cyrene

Eratosthenes of Cyrene was an ancient Greek scholar known for calculating the Earth’s circumference around 240 BCE. He used observations of shadows in two Egyptian cities, Alexandria and Syene, at the same time of day to measure the angle of the sun’s rays. By knowing the distance between the cities and the angle, he applied geometric principles to estimate the Earth’s circumference with remarkable accuracy. His work laid foundational principles in geodesy, the science of measuring Earth's shape, size, and gravitational field, demonstrating early scientific reasoning and the importance of observation in understanding the world.