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First calculation of the Earth radius
The Greek scientist Eratosthenes was the first in the world to calculate the radius of the Earth. The ancient Egyptians noticed that during the summer solstice the Sun illuminated the bottom of deep wells in Siena (now Aswan), but not in Alexandria. Eratosthenes used this fact to measure the circumference and radius of the Earth. On the summer solstice in Alexandria, June 19, 240 BC. Eratosthenes used a skafis (a bowl with a long needle) which helped him to determine the location angle of the Sun in the sky. The measured angle was 7 degrees 12 minutes, that is 1/50 of a circle. That means Siena is located 1/50 of the circumference of the Earth from Alexandria, that is 5000 stadia, therefore the circumference of the Earth was 250000 stadia, and the radius was 39790 stadia. It is unknown which stadion Eratosthenes used. If Greek (178 m) then the radius of the Earth was 7082 km, if Egyptian (172,5 m), then 6287 km. Modern measurements give a value of 6371 km for the average radius of the Earth. In any case the measurement accuracy was simply amazing for that time! |
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