In the year of his death, astronomer Nicolaus Copernicus (1473-1543; in Polish, Mikolaj Kopérnik) published De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres). This manuscript gave a full account of his theory that the Sun, and not the Earth, was at the center of the solar system (or universe). Although this theory was not new, Copernicus offered the idea in all its mathematical detail. This heliocentric (versus geocentric) view of the heavens, now known as the Copernican system, is the foundation of modern astronomy.