Went back and played with Eratosthenes today. There are a number of different ways to do this experiment. With a little work the diameter of the Sun is also derived.
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In 1906 (more or less) Wilbur Glenn Voliva from Zion City IL USA, did the math.
If the world is a 24000 mile diameter flat disk, then the same math puts the Sun at 3000 miles. (Sun is 32 miles across)
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Another way of thinking about Eratosthenes, look at the shadows of the poles.
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Another way of thinking about Voliva, look at the shadows of the poles.
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As I said to the tax man; "given enough math and enough numbers I can prove anything".