Eratosthenes (circa 284-192 B.C.E) made the most famous and accurate of the Greeks' estimates of the circumference of the earth. He found that at noon on the summer solstice, the sun was directly overhead at Syene, Egypt, at the same time 5000 stadia (approximately 500 miles) north, in Alexandria, Egypt, the sun was 1/50 of a circle off vertical. Make a diagram, compute the circumference of the earth based on his data and explain your procedure. [Hint: Eratosthenes assumed that the sun's rays at Syene and Alexandria were parallel.]

Guest Mar 12, 2015