How Good Was the Measurementof Eratosthenes?

• On a day when the sun was directly overhead at Syene (far southern Egypt)

• The angle at Alexandria (5000 stadia north) was 7.2 degrees, 1/50 of a full circle

• So the circumference of the earth must be 50 x 5000 stadia = 250,000 stadia

• Roughly 5% less than today’s accepted value! around 24,000 miles, 40,000 km

  • (Radius = Circumference /2 p)

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