  Nicolaus Copernicus (1473–1543) was a mathematician and astronomer who proposed that the sun was stationary in the center of the universe and the earth revolved around it. Disturbed by the failure of Ptolemy’s geocentric model of the universe to follow Aristotle’s requirement for the uniform circular motion of all celestial bodies and determined to eliminate Ptolemy’s equant, an imaginary point around which the bodies seemed to follow that requirement, Copernicus decided that he could achieve his goal only through a heliocentric model. He thereby created a concept of a universe in which the distances of the planets from the sun bore a direct relationship to the size of their orbits. At the time Copernicus’s heliocentric idea was very controversial; nevertheless, it was the start of a change in the way the world was viewed, and Copernicus came to be seen as the initiator of the Scientific Revolution.