The Ancient Experiment That Proved the Earth Is Round

Long before astronauts or satellites, a man named Eratosthenes used two sticks and some clever geometry to estimate the Earth's size—and prove it’s round. In 240 B.C., he observed that when the sun was directly overhead in Syene (modern-day Aswan), a stick in Alexandria (800 km north) cast a 7° shadow. That 7° difference meant Earth had to be curved—and he used it to calculate the planet’s circumference with surprising accuracy. It’s one of the earliest (and coolest) science wins in history. 🌍 Subscribe for more clever experiments from history that shaped the world.