CircumferenceEarth

CircumferenceEarth - Circumference of the Earth The Greeks...

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Circumference of the Earth The Greeks knew that the earth was spherical and derived estimates of its circumference. Eudoxus of Cnidos (408-355 BC) was supposed to have estimated the circumference of the earth to be 400,000 stades (circa 40,000 miles). The most famous of these estimates was given by Eratosthenes (276-196 BC). When he was in Syene in Cyrene he observed that the sun was directly overhead at midday during the summer solstice. He knew that in Alexandria, some 5000 stades directly north, the sun was not directly overhead. In Alexandria, a shadow equal to one fiftieth of a circle was cast. Assuming that the rays coming from the sun at both locations are parallel, the angle ! is determined by the curvature of the earth. In radian measure the circumference is given by 1 tan " 5000 stades = 50 " 5000 stades = 250,000 stades = 25,000 miles . This is a fairly good estimate compared to the current accepted value of 24,902 miles at the equator. Relative Distances to Moon and Sun
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CircumferenceEarth - Circumference of the Earth The Greeks...

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