Legacy of wisdom on Instagram: "Carl Sagan explained how the ancient Greeks knew the Earth was round—over 2,000 years ago. In Cosmos, he shared how Eratosthenes noticed that at noon on the summer solstice, the sun was directly overhead in Syene but cast a shadow in Alexandria. 📏 With just a stick and basic geometry, Eratosthenes measured the angle of the shadow and calculated the Earth’s circumference. His estimate? Shockingly close to what we know today—proving the Earth’s roundness with simpl