It took hundreds of years more, and the radical thinking of an astronomer named Nicolaus Copernicus, before the science of planetary motions would finally be set on its correct course. Copernicus proposed the theory that it was the sun and not the Earth that was at the center of the universe. This model—now known as the heliocentric or Copernican model—easily explained retrograde motion as well as a host of other problems apparent in the existing models. In fear of reprisal, however, from the Catholic Church, the main governing body at the time and a strong proponent of the geocentric universe, Copernicus delayed the publication of his theory until after his death in 1543.