He developed the heliocentric model of the solar system, which placed the Sun at the center and the Earth in orbit around it. This model contradicted the prevailing geocentric model, which had been held for centuries and placed the Earth at the center of the universe.

Copernicus published his groundbreaking work, "De Revolutionibus Orbium Coelestium" ("On the Revolutions of the Heavenly Spheres"), in 1543, just before his death. His work was initially met with skepticism and resistance, but eventually, it revolutionized our understanding of the universe.