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Geocentric or heliocentric?


This page demonstrates the difference between Ptolemy's idea of the solar system and that of Copernicus. It is meant to show why Ptolemy thought in terms of epicycles: circles upon circles. The 5 inner planets are shown in an oblique view. The only difference between the upper and lower diagrams is whether the Earth or the Sun is held fixed at the centre. Notice that the lines joining Earth to each planet form exactly the same relationships in the two diagrams at all times. You may alter the animation in various ways by clicking the buttons.

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The animation is programmed in Javascript.

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