Ancient Greek Wisdom Shines Through: Eratosthenes' Measurement of Earth's Size

It is remarkable that over two thousand years ago, the ancient Greeks were able to use reason and math to figure out that the Earth was not flat. This feat was achieved by Eratosthenes, a Greek mathematician who used geometry and trigonometry to calculate the circumference of the Earth. His calculations were remarkably accurate for his time and have been verified in modern times as well. The Cosmos episode featuring Carl Sagan explains how Eratosthenes made this discovery. He observed that on the summer solstice in Syene (modern-day Aswan), Egypt, there was no shadow cast from a vertical stick at noon. This meant that at this location, the Sun was directly overhead. He then measured the angle of a shadow cast from a vertical stick in Alexandria, which he determined to be about 7°12'. From these observations, he calculated that since Syene and Alexandria were about 5,000 stadia apart (about 800 km), then the circumference of Earth must be 50 times greater than this distance or approximately 40,000 km—a number remarkably close to today’s accepted value of 40,075 km! Eratosthenes’ work is an example of human ingenuity and determination in understanding our world better. Despite living over two thousand years ago with limited resources available compared to today’s technology and science advancements, he still managed to make incredible progress towards understanding our planet better. His work serves as an inspiration for us all as we continue exploring our universe with curiosity and passion for knowledge!