Copernican heliocentrism is the astronomical model developed by the Renaissance astronomer Nicolaus Copernicus and published in 1543. This model positioned the Sun near the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths, modified by epicycles, and at uniform speeds. The Copernican model challenged the geocentric model of Ptolemy that had prevailed for centuries, which had placed Earth at the center of the Universe.