The Copernican Revolution describes the transition from a Ptolemaic universe, with Earth fixed at the center, to heliocentrism, in which Earth rotates and orbits the Sun. Nicolaus Copernicus preserved many ancient assumptions, including circular orbits and uniform motion, but removed Ptolemy’s equant and explained planetary retrograde motion through Earth’s movement. His ideas drew on earlier Greek and Islamic astronomical debates and gained force after Galileo’s telescope revealed lunar irregularities, Jupiter’s moons, and Venus’s complete phases. Religious controversy followed, culminating in restrictions on Copernican books and Galileo’s 1633 house arrest. The revolution also became a cultural metaphor and inspired the Copernican principle: humans are not privileged observers of the universe.