How One Greek Scientist Measured the Earth With a Shadow

Over 2,200 years ago, before telescopes or satellites, one Greek genius proved the Earth was round and then measured its size. His only tools? A well, a stick, and the shadow it cast. This is the true story of Eratosthenes, the brilliant head librarian at the legendary Library of Alexandria. He heard a report that on the summer solstice, the sun shone directly down a deep well in the city of Syene (modern Aswan), casting no shadow. But in his own city of Alexandria, on the very same day at the same time, a vertical stick did cast a shadow. In that simple observation, Eratosthenes saw the curvature of the Earth. Using simple geometry (and a bit of pacing), he performed the first-ever scientific calculation of our planet's circumference. This channel is dedicated to bringing you the true, forgotten, and unbelievable facts from history. Join us as we explore the simple, elegant experiment that revealed the size of our entire world. In this video, we'll uncover the historical facts: Who was Eratosthenes (the "father of geography")? The key observation: The well in Syene vs. the shadow in Alexandria. The simple math he used (and how you could do it, too). How astonishingly accurate was his final calculation? (The answer will shock you). Why this one experiment is one of the most important moments in human thought. If you love learning about real history and moments of human genius, make sure to subscribe for more! 🔔 SUBSCRIBE for more true history stories: