Why did Aristotle think the earth is spherical?
The greeks at the time of Aristotle actually measured the distance to the moon in terms of earth diameters, based upon the length of time it took earth’s shadow to cross the lunar surface. The calculated 60 diameters, a figure that was quite accurate. What they did not know was how big the earth was, at that time. A couple of centuries later the clever greek who was head of the Library at Alexandria, Eratosthenes, figured out a way to measure the breadth of the earth. His figure was pretty close to the currently accepted value, and thus the greeks developed a pretty good concept of the size of the solar system. Aristarchus, who lived around the time of Aristotle, also developed a heliocentric (sun centered) model of the solar system, which placed the sun out some 20 times further than the moon, but most educated greeks rejected his model.
