How did Eratosthenes measure the size of the earth?

1 Answer
A. S. Adikesavan
Mar 14, 2016

From the shadow angle of a tower in Alexandria at Summer Solstice noon and identifying the angle it with the angle subtended by the Earth's arc between Alexandria and Syene, in the year 240 BC.

Explanation:

The angle identified was about 360/5 = 72 deg.

The circumference was approximated by Eratosthenes, with an error of about 1% against the current precision.

History speaks of computational ability in humans, over millenniums.
I am glad that the questioner brought this to Socratic notice.

My reference: www.windows2.universetoday.org/.../eratosthenes-calc-earth-size.html

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