Question: how eratosthenes calculated the circumference of the earth?
Answer: Eratosthenes then measured the angle of a shadow cast by a stick at noon on the summer solstice in Alexandria, and found it made an angle of about 7.2 degrees, or about 1/50 of a complete circle. ... Eratosthenes then used this to calculate the circumference of the Earth to be about 250,000 stadia.