Copernican heliocentrism

A model of the planetary system that places the Sun near its center and explains Earth’s daily and yearly motions through rotation and revolution.

Retrograde motion: The apparent reversal of a planet’s direction against the stars as seen from Earth. Earth overtakes outer planets, making their apparent backward loops intelligible without treating them as real reversals.
Nicolaus Copernicus: A Renaissance astronomer whose work placed the Sun near the center of the known planetary system. His calculations and arguments gave the heliocentric model its influential systematic form.
Galileo Galilei: An Italian astronomer and physicist whose telescopic observations supported a changing account of the heavens. His observations of Venus and Jupiter’s moons strengthened arguments against strict geocentrism.
Geocentric model: A model that places Earth at the center of the cosmos or planetary system. It is the central rival to the Sun-centered arrangement proposed by Copernicus.
Earth's rotation: Earth’s daily spin about its axis, which produces the apparent daily motion of the sky. Copernicus assigned the daily turning of the heavens to Earth’s rotation.
De revolutionibus orbium coelestium: Copernicus’s 1543 book presenting a mathematical model of a Sun-centered planetary system. This book published the model that became known as Copernican heliocentrism.
Johannes Kepler: A German astronomer who described planetary orbits as ellipses and formulated three laws of planetary motion. Kepler replaced Copernicus’s circles with elliptical orbits, improving the heliocentric model’s accuracy.
Tychonic system: A model in which the Sun orbits a stationary Earth while the other planets orbit the Sun. Tycho Brahe’s arrangement preserved a stationary Earth while adopting much of the heliocentric geometry.
Earth's orbit: The path Earth follows around the Sun over the course of a year. Earth’s annual revolution replaces the moving celestial sphere as the basis of yearly sky changes.
Aristarchus of Samos: An ancient Greek astronomer who proposed that Earth revolves around a stationary Sun. His surviving proposal shows that heliocentric ideas predated Copernicus by many centuries.

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