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near to which all the planets in their orbits
pass, thus facilitating the determination of
planetary motions. Aristarchus (320-250 B.C.)
showed that the sun must be at least nine-
teen times as far off as the moon, which
is far short of the mark. He also found
the sun’s diameter, correctly, to be half a
degree. Eratosthenes (276-196 B.C.) mea-
sured the inclination to the equator of the
95