Earth's Diameter

Paper Summary:

This paper describes Eratosthenes' calculation of the Earth's diameter, based on one assumption and two measurements, that the Earth was a sphere and that the two measurements made are the degree of the Earth's shadow at noon at two points and the distance between those points. It outlines how this experiment can be repeated by measuring the degree of the shadows cast at two locations either directly north or south of each other at noon on the same day and details the equipment required, the measurements to be taken and the mathematical equations involved.

From the Paper:

"Eratosthanes used the city of Syene in Egypt as the first point. This point was selected because it was known that on noon on the first day of summer the sun was directly overhead. This was known because people observed that at this time, the buildings cast no shadows (York University). Therefore, the degree of the shadow at Syene was 0o.
Eratosthanes then needed to know the degree of the shadow at another point either directly north or directly south, at the same time of day. Eratosthanes selected Alexandria as the second city. The degree of the sun's shadow was measured and found to be 7.2o (HEASARC)."

More papers on Earth's Diameter:

• Essay # 6252 : "Living in Partnership with the Earth"
• Essay # 85504 : "Life on Planet Earth"
• Essay # 88582 : "Eratosthenes and Measurement"

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