He was a Greek mathematician and the head librarian at the Library of Alexandria who made history over 2200 years ago with a simple yet ingenious experiment.
Eratosthenes became the first person to calculate the Earth’s circumference with remarkable accuracy, a feat that stands as a testament to the ingenuity of ancient science.
Using the differences in the angle of the sun’s rays at two different locations, Eratosthenes was able to estimate the Earth’s circumference. He observed that at noon during the summer solstice in Syene (modern-day Aswan, Egypt), the sun cast no shadow as it was directly overhead.
However, at the same time in Alexandria, a noticeable shadow was cast by a stick. By measuring the angle of this shadow and knowing the distance between the two cities, he could use basic geometry to estimate the Earth’s size.
His method was straightforward: he measured the length of a shadow from a vertical stick of a known height in two cities on the same day. The ratio between the north-south distance between the two cities and the angles measured gave a ratio that allowed Eratosthenes to calculate the size of the Earth.
Eratosthenes’ calculation of the Earth’s circumference was approximately 40,000 kilometers, which is remarkably close to the modern measurement of 40,075 kilometers.
His work laid the foundation for geography and demonstrated that even in ancient times, humanity had a deep understanding of the world. Eratosthenes’ legacy continues to inspire us, showing that curiosity and critical thinking can lead to extraordinary discoveries.
READ MORE: The Only Illustrated Manuscript of Homer’s Iliad from Antiquity.