What key idea did Copernicus contribute to the Renaissance?

The key idea contributed by Copernicus is that the earth revolved around the sun rather than the other way around. This theory, known as "heliocentrism" was very radical. Copernicus's contemporaries, and most importantly the Catholic Church, accepted the ancient Ptolemaic theory, a "geocentric" model that placed the earth at the center of the universe. According to this model, the Earth was stationary. This view accorded with a literal understanding of the Bible, which, in several passages, seems to portray the Earth as a non-moving body. Copernicus's theory, published in the last year of his life in a book entitled De Revolutionibus, thus flew in the face of Church doctrine, and was banned by the Church. It should be noted that Copernicus's model needed significant revision, as it argued that the sun was at the center of the universe, with all the stars and other heavenly bodies revolving around it as well. Like Ptolemy, he thought orbits were traced along perfect spheres. Later astronomers, working from observation, showed that orbits were in fact elliptical, and that the sun was not the center of the universe.