Science: Taping the Earth
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Now Eratosthenes had all the information he needed. The shadow cast by the vertical pillar at Alexandria would have the same relation to a full circle that the distance from Alexandria to Syene (where sunlight was vertical) would have to the circumference of the earth. The answer: 250,000 stadia (21,913 nautical miles), which is remarkably accurate. The latest measurement of the earth's circumference around the poles: 21,580 nautical miles.
*The international nautical mile (6,076.10 ft.) is used on long-distance charts. For purposes of navigation it is considered one minute of longitude, although it is derived from the standard meter, not directly from the earth's circumference at the equator.
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