Transcript: Aristarchus, who lived in the third century BC, was a skilled geometer, and he anticipated the Copernican heliocentric model by over 1800 years.  He deduced by application of logic and geometry that the sun must be 19 or 20 times larger and further away than the moon.  Knowing that the sun was larger than the Earth it made no sense for the sun to go around the smaller Earth.  Rather, Aristarchus supposed that the smaller object went round the larger object.  He used the analogy of a hammer-thrower to make this clear.  In Aristarchus's heliocentric model the stars had to be extremely far away so that we would not see the variation in their relative position and brightness as the Earth moved around the Sun.  Aristarchus also measured a highly accurate solar year.