The Copernican system is a model of the solar system in which the Sun is positioned at or near the center, with Earth and the other planets orbiting it. It is named for the Polish mathematician and astronomer Nicolaus Copernicus (b. 19 February 1473; d. 24 May 1543), who presented the model systematically in his De revolutionibus orbium coelestium (1543). The system stands in contrast to the Ptolemaic system, which placed Earth at the center of the cosmos. The Copernican model is historically significant as a foundational development in what later came to be called the Scientific Revolution.

In the Copernican system, the Sun occupies a central (or near-central) position, and the six planets known in Copernicus's time - Mercury, Venus, Earth, Mars, Jupiter, and Saturn - orbit it in circular paths. Earth rotates on its own axis once per day, producing the apparent daily motion of the heavens, and completes one orbit of the Sun per year. The Moon orbits Earth. Copernicus retained several features of earlier astronomical tradition, including the use of circular orbits and a version of the epicycle to account for observed irregularities in planetary motion; his system was therefore not a complete break from Ptolemaic mechanics, but a fundamental reordering of the celestial hierarchy.

The model offered a natural explanation for several phenomena that required elaborate contrivance under the Ptolemaic system, including the retrograde motion of the outer planets and the fixed relationship between the elongations of Mercury and Venus and the Sun. It also implied a vastly larger universe than previously assumed, since stellar parallax - the apparent shift in star positions that should result from Earth's orbit - was not observed, requiring the fixed stars to lie at enormous distances.

Copernicus circulated an early sketch of his ideas in a manuscript known as the Commentariolus (c. 1514) before publishing the full account in De revolutionibus in the final year of his life. The preface to the published edition, added without Copernicus's authorization by the Lutheran theologian Andreas Osiander, described the model as a mathematical convenience rather than a physical claim - a characterization that has been contested by historians regarding Copernicus's own intent. For a fuller account of the system's origins and reception, see Copernican System - History.

The heliocentric structure of the solar system - Earth and other planets orbiting the Sun - is accepted as physically correct in contemporary astronomy and physics. The astronomical consensus holds the Copernican system (as later refined by Kepler's elliptical orbits and Newton's gravitational mechanics) to be an accurate description of solar system structure. Questions that remain active in scholarship concern the history, reception, and philosophical interpretation of the original Copernican proposal, not the underlying heliocentric claim.

• Heliocentric consensus view - The mainstream position in modern astronomy accepts heliocentrism as physically correct, with Copernicus's circular-orbit model superseded by Keplerian ellipses and Newtonian dynamics. See Heliocentric Consensus Viewpoint.

• Instrumentalist interpretation - Some philosophers and historians of science, following the framing introduced by Osiander, have treated the Copernican model as a calculating device whose truth-value is a separate question from its predictive utility. See Instrumentalist Viewpoint.

• Geocentric and geostatic dissent - A minority of contemporary dissenters, drawing variously on religious texts or alternative interpretations of physical evidence, maintain some form of geocentric or geostatic cosmology. See Geocentric Dissent Viewpoint.

• Neo-Tychonic model - Some critics of strict Copernicanism have advocated the Tychonic system or variants, in which the Sun orbits Earth while the other planets orbit the Sun, as an empirically equivalent alternative. See Neo-Tychonic Viewpoint.

• Copernican System - History
• Copernican System - Debate
• Copernican System - Astronomy Consensus
• Ptolemaic System
• Tychonic System
• Scientific Revolution
• De revolutionibus orbium coelestium
• Galileo Affair
• Kepler's Laws

1. Copernicus, Nicolaus. De revolutionibus orbium coelestium. Nuremberg: Johannes Petreius, 1543.
2. Copernicus, Nicolaus. Commentariolus (c. 1514). Trans. in Edward Rosen, Three Copernican Treatises. New York: Columbia University Press, 1939.
3. Gingerich, Owen. The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus. New York: Walker & Company, 2004.
4. Kuhn, Thomas S. The Copernican Revolution: Planetary Astronomy in the Development of Western Thought. Cambridge: Harvard University Press, 1957.
5. Rosen, Edward. “Osiander's Introduction to Copernicus' De revolutionibus.” Isis 43, no. 1 (1952): 20-24.
6. Dreyer, J.L.E. A History of Astronomy from Thales to Kepler. 2nd ed. New York: Dover, 1953.