- Greek philosopher
and astronomer who may have been the first to realize that the Earth
turns on its axis, from west to east, once every 24 hours. He also thought
that the observed motions of Mercury and Venus suggested that they orbited
the Sun rather than the Earth.
Born in Heraklea, near the Black Sea, Heraklides migrated to Athens
and studied at the Academy of Plato. He is said also to have attended
the schools of the Pythagorean philosophers, and would thus have come
into contact with Aristotle. All his writings are lost, so his astronomical
theories are known only at second hand.
In proposing the doctrine of a rotating Earth (not to be accepted for
another 1,800 years), Heraklides contradicted the accepted model of
the universe put forward by Aristotle. Heraklides thought that the immense
spheres in which the stars and planets were assumed to be fixed could
not rotate so fast.
He did not completely adopt the heliocentric view of the universe stated
later by Aristarchus, but proposed instead that the Sun moved in a circular
orbit (in its sphere) and that Mercury and Venus moved on epicycles
around the Sun as centre.
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