The round shape of the Earth may be inferred from the existence of a horizon at sea. Ancient Greeks deduced it from the shape of the Earth's shadow when the Moon is eclipsed and from stars visible only in southern countries. Eratosthenes accurately estimated the size of the Earth, but Columbus based his plans on an incorrect value, by which India would be much closer to Spain.
%0 Electronic Source %A Stern, David %D December 12, 2004 %T The Round Earth and Christopher Columbus %V 2013 %N 19 May 2013 %8 December 12, 2004 %9 text/html %U http://www.phy6.org/stargaze/Scolumb.htm
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