Co·per·ni·cus(kō-pûr′nə-kəs, kə-), Nicolaus 1473-1543.
Polish astronomer who proposed a heliocentric model of the universe, contradicting the Ptolemaic system that had dominated medieval cosmology.
Co·per·ni·cus(kō-pûr′nə-kəs), Nicolaus 1473-1543.
Polish astronomer whose theory that Earth and other planets revolve around the sun provided the foundation for modern astronomy. He also proposed that the Earth turns once daily on its own axis.
Biography The man who devised one of astronomy's most important theories wasn't even a trained astronomer: Nicolaus Copernicus practiced medicine, and he wrote the work that made him famous in his spare time. In the first, brief version of his theory, Copernicus set out his heliocentric system, stating that the sun is at the center of the universe and that all the planets and stars revolve around it in circular orbits. In doing so, Copernicus was trying to explain the observed movements of the planets—those that, in the days before telescopes, were visible to the naked eye. These movements did not fit the older, Earth-centered (or geocentric) model of the universe devised by the Greek astronomer Ptolemy. Copernicus's sun-centered model offered a more accurate accounting of planetary movement. He published a longer, more complete account of his theory in 1543, just before he died. Almost all of his contemporaries doubted that his system could be true, and they kept working with the older, geocentric model. After Copernicus died, there were a few people who defended his model, including the astronomers Johannes Kepler and Galileo Galilei. But it took almost 150 years for the Copernican theory to take hold, when Sir Isaac Newton published his theory of universal gravitation.