The Copernican Revolution:
The Copernican model consisted of the Sun at the centre with the six planets, Mercury, Venus, the Earth with the Moon-round it, Mars, Jupiter and Saturn going round it in circular orbits. In this model too the stars formed a fixed sphere in the background. Copernicus also believed all planets to be of the same size. His model worked as well as Ptolemy's spheres in explaining the apparent motion of the planets. But it led to a confrontation with the adherents of geocentric model. It was not generally accepted until much later when Galilee's and Kepler's works proved that the heliocentric model was valid.
Fig: Copernican system
The sun-centred model of Copernicus was established by the astronomical observations of Galileo Galilei when in 1609, he turned his small, imperfect telescope towards the sky. In the first few nights of observs:ion of the heavens, Galileo saw enough to shatter the ancient picture of the serene, perfect, harmonious world.