Copernican heliocentrism

Copernican heliocentrism is the astronomical model developed by Nicolaus Copernicus and published in 1543. This model positioned the Sun near the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths, modified by epicycles, and at uniform speeds. The Copernican model challenged the geocentric model of Ptolemy that had prevailed for centuries, which had placed Earth at the center of the Universe.

Although Copernicus had circulated an outline of his own theory to colleagues sometime before 1514, he did not decide to publish it until he was urged to do so later by his pupil Rheticus. His model was an alternative to the longstanding Ptolemaic model that purged astronomy of the equant in order to satisfy the philosophical ideal that all celestial motion must be perfect and uniform, preserving the metaphysical implications of a mathematically ordered cosmos. His heliostatic model retained several false Ptolemaic assumptions such as the planets' circular orbits, epicycles, and uniform speeds, while at the same time using accurate ideas such as:

  • The Earth is one of several planets revolving around a stationary sun in a determined order.
  • The Earth has three motions: daily rotation, annual revolution, and annual tilting of its axis.
  • Retrograde motion of the planets is explained by the Earth's motion.
  • The distance from the Earth to the Sun is small compared to the distance from the Sun to the stars.

The Copernican model was later replaced by Kepler's laws of planetary motion.

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