A Polish savant, he studied in Italy. He was the first modern astronomer who endeavoured to demonstrate that the Earth was not the fixed centre of the Universe, as had been believed up until then, but a planet amongst others gravitating around the Sun. In breaking with this ancient geocentric conception of the world in favour of a heliocentric conception, Copernicus marked a major turning point in the history of though and the sciences. If a ‘Copernican revolution’ is often quite rightly spoken off, it is also for reasons of methodology: in substituting the principle of facts for the authority of the Ancients as the source of all knowledge, Copernicus stamped an essential turning point on scientific research. But he could not in his lifetime provide any decisive proof of his heliocentric hypothesis, which would not be validated until after the discoveries made by Galileo, following the invention of the astronomical telescope. The works of Copernicus were thus condemned by the Church and placed on the Index.