How Ancient Greek mathematician Eratosthenes calculated the Earth’s circumference (VIDEO)
The idea that Earth is a sphere was first introduced by another ancient Greek mathematician, Pythagoras, around 500 BC and validated by Aristotle about 200 years later
Carl Sagan explains how the ancient Greeks figured out the Earth isn’t flat, over 2,000 years ago
Sagan devoted much of his life to countering anti-science trends