Part 3/10:
The ancients first inferred the Earth's roundness through lunar observations, particularly during eclipses when Earth's shadow projected onto the Moon clearly demonstrated its spherical form. Tao notes that ancient thinkers could deduce the Earth's shape solely by observing these celestial events without complex instruments.
Eratosthenes and the Size of the Earth
A compelling tale unfolds with Eratosthenes, the ancient Greek scholar credited with the first known measurement of the Earth’s circumference. Inspired by an account of a well in Syene, where the Sun was seen directly overhead during the summer solstice, he decided to conduct a simple experiment in Alexandria on the same day.