Nicolaus Copernicus’s book On the Revolutions of the Heavenly Spheres is added to the Index of Forbidden Books 73 years after it was first published.

On the Revolutions of the Heavenly Spheres (*Latin: De revolutionibus orbium coelestium) is the groundbreaking astronomical work published in 1543 by Nicolaus Copernicus. In this book, Copernicus proposed a radical alternative to the long-accepted Earth-centered universe described by Claudius Ptolemy. Instead of placing Earth at the center of the cosmos, Copernicus argued that the Sun sits near the center and that Earth is one of several planets orbiting it. This heliocentric model explained planetary motions—such as retrograde motion—more simply than the geocentric system. The book was written in dense mathematical language and included geometric diagrams that allowed astronomers to calculate planetary positions.

The structure of the book reflects its scientific ambition. It is divided into six books, beginning with general cosmological principles and then progressing into increasingly technical discussions of planetary motion. Copernicus maintained that Earth rotates daily on its axis and revolves annually around the Sun, which accounts for the apparent movement of the stars and the changing seasons. Although Copernicus still used circular orbits and epicycles inherited from earlier astronomy, his system dramatically shifted the perspective of the universe by removing Earth from the central position. This conceptual change challenged centuries of philosophical and theological assumptions about humanity’s place in the cosmos.

The publication of On the Revolutions of the Heavenly Spheres marked the beginning of what historians call the Copernican Revolution. While the book was initially read mostly by mathematicians and astronomers due to its complexity, its ideas gradually transformed scientific thinking. Later figures such as Johannes Kepler and Galileo Galilei built upon Copernicus’s work, refining the heliocentric model and providing observational evidence that strengthened it. Ultimately, Copernicus’s book reshaped humanity’s understanding of the universe and laid the foundation for modern astronomy