&quot;...the Greek philosopher Eratosthenes noted that the sun cast a shadow of different lengths at different latitudes (all the shadows would be the same length if the earth&#x27;s surface were flat).&quot;<p>This is an interesting statement, because it means he had some idea of how far away the sun was from the Earth.  If  it was, say, a thousand miles up, you&#x27;d see huge differences in shadow length depending on where you were standing on a flat earth.  Since it&#x27;s tens of millions of miles away, the difference is negligible.