Answer
Nicolaus Copernicus did not know that Aristarchus of Samos had developed a heliocentric model of the Solar System, in which the Sun, not Earth, was the center of the universe. Copernicus' heliocentric theory, published in his book "On the Revolutions of the Heavenly Spheres," was a significant departure from the prevailing geocentric model and laid the groundwork for modern astronomy.