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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Copernican Revolution | 1/5 | https://en.wikipedia.org/wiki/Copernican_Revolution | reference | science, encyclopedia | 2026-05-05T12:41:57.697069+00:00 | kb-cron |
Copernican Revolution is a phrase with different meanings in different contexts. In astronomy, the phrase refers to the transition from geocentrism to heliocentrism. For Christianity and Western culture, it may instead refer to the dismantling of the human-centric medieval cosmology and its cultural consequences. In physical cosmology, the phrase may be used to refer to the emergence and formalization of the Copernican principle that humans are not privileged observers of the universe. Within the philosophy of science, the Copernican Revolution is the first historic example of a paradigm shift in science. Finally, the phrase is sometimes used by English speakers as a metaphor for any radical intellectual upheaval that fundamentally reorders or reshapes our understanding of the world. The Copernican Revolution is named for the Renaissance astronomer Nicolaus Copernicus, who in the 16th century proposed that the Earth revolves around the Sun. Driven by a desire for a more perfect (i.e. circular) description of the cosmos than the prevailing Ptolemaic model - which posited that the Sun circled a stationary Earth - Copernicus instead advanced a heliostatic model where a stationary Sun was located near, though not precisely at, the center of the heavens.
== Heliocentrism ==
=== Almagest ===
The idea of heliocentrism - a Sun-centered Universe - can be traced back to Aristarchus of Samos, a Hellenistic author writing in the 3rd century BC, who may in turn have been drawing on even older concepts in Pythagoreanism. Ancient heliocentrism was, however, eclipsed by the geocentric model presented by Ptolemy in the Almagest (c. AD 150) and accepted in Aristotelianism. European scholars were well aware of the problems with Ptolemaic astronomy by the 13th century. The debate was precipitated by the reception of Averroes's criticism of Ptolemy and it was revived by the recovery of Ptolemy's text and its translation into Latin in the mid-15th century. The mathematician and science historian Otto E. Neugebauer argues that the debate in 15th-century Latin scholarship must also have been influenced by the criticism of Ptolemy that was produced, after Averroes, in the Ilkhanid-era (13th to 14th centuries) Persian school of astronomy associated with the Maragheh observatory (especially the works of Al-Urdi, Al-Tusi and Ibn al-Shatir). Copernicus learned about Ptolemy's model when he was a university student through Theoricae novae planetarum by Georg von Peuerbach, compiled from lecture notes by Peuerbach's student Regiomontanus and printed in 1472. Regiomontanus himself was the teacher of Domenico Maria Novara da Ferrara, who was in turn the teacher of Copernicus.
=== Purging the Equant ===
Copernicus studied at Bologna University during 1496–1501, where he became the assistant of Domenico Maria Novara da Ferrara. He is known to have studied the Epitome in Almagestum Ptolemei by Peuerbach and Regiomontanus (printed in Venice in 1496) and to have performed observations of lunar motions on 9 March 1497. In De revolutionibus orbium coelestium, published in 1543, Copernicus attempted to align his work as closely as possible with Ptolemaic tradition. A comparison of his work with the Almagest shows that he followed Ptolemy's methods and even his order of presentation. Yet, in order to purge astronomy of the equant - which violated the theological and philosophical ideal that all celestial motion must be perfect and uniform - Copernicus challenged Ptolemy’s geocentrism, an orthodoxy that had prevailed for over a millennium. Copernicus' heliostatic model (with a stationary Sun located near, though not precisely at, the mathematical center of the heavens) retained several false Ptolemaic assumptions such as the planets' circular orbits, epicycles, and uniform speeds, but also included accurate ideas such as:
The Earth is one of several planets revolving around the Sun in a determined order. The Earth rotates daily on its axis and revolves annually about the Sun. 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. In The Sleepwalkers, the author and journalist Arthur Koestler writes that De revolutionibus orbium coelestium "was and is an all-time worst-seller." Discovering a first edition of De revolutionibus that had been extensively annotated by the leading teacher of astronomy in Europe in the 1540s - which seemed to contradict Koestler - the astronomer and science historian Owen Gingerich spent three decades tracking down and personally examining all existing first and second editions of Copernicus' major work. He not only established that De revolutionibus was widely read by 16th century astronomers but also what they thought of it:
Reinhold and his many followers admired Copernicus for a quite different aesthetic idea, the elimination of the equant. Copernicus devoted the great majority of De revolutionibus to showing how this could be done. While he had eliminated all of Ptolemy's major epicycles, merging them all into the Earth's orbit, he then introduced a series of little epicycles to replace the equant, one per planet. Because this made the motion uniform in each Copernican circle, the anti-equant aesthetic was satisfied. My Copernican census eventually helped to establish that the majority of sixteenth-century astronomers thought eliminating the equant was Copernicus' big achievement, because it satisfied the ancient aesthetic principle that eternal celestial motions should be uniform and circular or compounded of uniform and circular parts.