What relationship between the Sun and Earth did Copernicus formulate?

Answer 1

Copernicus changed the accepted heirarchy in the universe by producing a new model of the planets' movements among the fixed stars, as they were called.

The accepted model by Ptolemy, who lived in the Roman Empire, had the Earth at the centre of everything, with the Moon, Sun and everything else orbiting round it. The old model used circles and epicycles to explain the planets' orbits round the Earth (an epicycle is a small circle whose centre moves round a larger circle).

Copernicus devised an alternative model with the Sun at the centre instead, with the planets including Earth in orbit around it. He found that the new model required smaller epicycles, much small for Mercury, Venus and Mars, and this made him think it was preferable because the orbits were much closer to a simple circular shape instead of the complicated paths of the Ptolemaic system.

Copernicus did not publish the new model until the year he died, 1543, because he knew it was contrary to current religious teaching and he had no way of finding which model was more correct because both models represented the planets' movements reasonably accurately. But his work encouraged other scientists who came after him to study the problem, and the model that finally gained acceptance was Kepler's model, published in 1609, which did away with the old circles and epicycles and used elliptical orbits instead.

Kepler retained the idea of putting the Sun at the centre and this model was later accepted after it was explained by the laws of motion and the law of gravity.