What was the first scientist to dispute Ptolemy's model of a genetic or earth centered?

Answer 1

Copernicus devised an alternative model to explain the planets' movements among the stars. It was similar to Ptolemy's model in that it was composed of circles and epicycles, but it differed in placing the Sun at the centre instead of the Earth. So Ptolemy's model was geocentric while Copernicus's was heliocentric.

Copernicus had no way of testing the validity of his model except that it was geometrically simpler, especially for the inner planets Mercury, Venus and Mars which needed much smaller epicycles in Copernicus's model. We now know that the large epicyces in the Ptolemaic model were necessary to compensate for the Earth's movement round the Sun.

Galieo's discoveries with the telescope raised more serious doubts about Ptolemy's model when he found that Venus showed phases that could not be explained by the Ptolemaic model. The gibbous phase is not explained by Ptolemy's model because it does not allow Venus to go behind the Sun as seen from Earth.

Tycho produced a model that was geocentric but also explained the phases of Venus.

Finally all three models were rejected in favour of Kepler's model, which has the Sun at the centre and the planets in elliptical orbits. This is the model used today, with very minor modifications due to the General Theory of Relativity.