In astronomy, the Copernican Revolution refers to the transition from geocentrism to heliocentrism. For Christianity and Western culture, the term may refer to the dismantling of the human-centric medieval cosmology and its cultural consequences. Within the philosophy of science, the Revolution is the first historic example of a paradigm shift in science. Finally, the term 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 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.
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 and accepted in Aristotelianism.
Martianus Capella (5th century CE) expressed the opinion that the planets Venus and Mercury did not go about the Earth but instead circled the Sun. Capella's model was discussed in the Early Middle Ages by various anonymous 9th-century commentators and Copernicus mentions him as an influence on his own work. Macrobius (420 CE) described a heliocentric model. John Scotus Eriugena (815-877 CE) proposed a model reminiscent of that from Tycho Brahe.
European scholars were well aware of the problems with Ptolemaic astronomy by the 13th century. The debate was precipitated by the reception by Averroes's criticism of Ptolemy, and it was again revived by the recovery of Ptolemy's text and its translation into Latin in the mid-15th century. Otto E. Neugebauer in 1957 argued that the debate in 15th-century Latin scholarship must also have been informed by the criticism of Ptolemy produced after Averroes, by 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).
The state of the question as received by Copernicus is summarized in the Theoricae novae planetarum by Georg von Peuerbach, compiled from lecture notes by Peuerbach's student Regiomontanus in 1454 but printed only in 1472. Peuerbach attempts to give a new, mathematically more elegant presentation of Ptolemy's system, but he does not arrive at heliocentrism. Regiomontanus himself was the teacher of Domenico Maria Novara da Ferrara, who was in turn the teacher of Copernicus.
There is a possibility that Regiomontanus already arrived at a theory of heliocentrism before his death in 1476, as he paid particular attention to the heliocentric theory of Aristarchus in a later work, and mentions the "motion of the Earth" in a letter.
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. An early short work, Commentariolus, written some time before 1514, circulated in a limited number of copies among his acquaintances.
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 PtolemyâÂÂs 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:
In , Arthur Koestler wrote 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 - 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: <blockquote> 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. </blockquote>
Copernicus' challenge reached 16th-century astronomers but failed to displace the dominance of Ptolemy's geocentrism, which only fell out of favor among astronomers after Galileo's telescopic observations of 1610. But Copernicanism did gain a handful of supporters in the 16th century. Thomas Digges and Giordano Bruno used Copernicus' new estimate of the distance to the stars to argue for an indefinitely extended or even infinite universe in opposition to the ancient orthodoxy of celestial spheres. William Gilbert also argued (correctly) that Copernicus was right about the Earth rotating on its axis (instead of an outer "shell" of rotating stars) while also arguing (incorrectly) that the mechanism of the Earth's rotation is magnetism.
Copernicus was a canon, a lifelong official of the Catholic Church. Even before his death in 1543 and during the following 70 years (until 1610), his model faced withering criticism from Protestant leaders who were locked in combat with the Church, were often animated by a fierce anti-clericalism and typically adopted a literalist approach to Scripture. Protestant leaders Martin Luther and Philip Melanchthon both attacked Copernicus. Luther famously cited the Book of Joshua to prove the sun moves and reportedly called Copernicus a "fool." His colleague Melanchthon urged governments to repress the "absurd" theory. Meanwhile, the Catholic Church indirectly used Copernican mathematics in its reform of the Gregorian calendar in 1582 and otherwise, until 1610, remained officially silent on either the merits or demerits of Copernicanism.
Galileo Galilei, sometimes referred to as the "father of modern observational astronomy," developed his own telescope with enough magnification to allow him to study Venus and discover that it has phases like a moon. His improvements to the telescope, astronomical observations, and support for Copernicanism were all integral to the Copernican Revolution.
Based on the designs of Hans Lippershey, Galileo designed his own telescope which, in the following year, he had improved to 30ÃÂ magnification. Using this new instrument, Galileo made a number of astronomical observations which he published in the Sidereus Nuncius in 1610. In this book, he described the surface of the Moon as rough, uneven, and imperfect. He also noted that "the boundary dividing the bright from the dark part does not form a uniformly oval line, as would happen in a perfectly spherical solid, but is marked by an uneven, rough, and very sinuous line, as the figure shows." These observations challenged Aristotle's claim that the Moon was a perfect sphere and the larger idea that the heavens were perfect and unchanging.
Galileo's next astronomical discovery would prove to be a surprising one. While observing Jupiter over the course of several days, he noticed four stars close to Jupiter whose positions were changing in a way that would be impossible if they were fixed stars. After much observation, he concluded these four stars were orbiting the planet Jupiter and were in fact moons, not stars. This was a radical discovery because, according to Aristotelian cosmology, all heavenly bodies revolve around the Earth and a planet with moons obviously contradicted that popular belief. While contradicting Aristotelian belief, it supported Copernican cosmology which stated that Earth is a planet like all others.
In 1610, Galileo observed that Venus had a full set of phases, similar to the phases of the moon we can observe from Earth. This was explainable by the Copernican or Tychonic systems which said that all phases of Venus would be visible due to the nature of its orbit around the Sun, unlike the Ptolemaic system which stated only some of Venus's phases would be visible. Due to Galileo's observations of Venus, Ptolemy's system became highly suspect and the majority of leading astronomers subsequently converted to various heliocentric models, making his discovery one of the most influential in the transition from geocentrism to heliocentrism.
Galileo's Letters on Sunspots, which reported his 1610 telescopic observations of the full set of phases of Venus, was published in 1613. In his 1615 Letter to the Grand Duchess Christina, Galileo argued that the language of the Bible had been accommodated to be understandable to uneducated people and should therefore not be interpreted as literal scientific descriptions and the Church risked reputational damage in the long run if it officially condemned heliocentrism. He invited the Church to follow established practice and reinterpret Scripture in light of the new scientific discoveries, quoting Cardinal Baronius: "The Holy Ghost intended to teach us how to go to heaven, not how the heavens go."
Galileo received staunch support from a Carmelite friar, Paolo Antonio Foscarini, who published a book defending Galileo's heliocentrism and presenting it as compatible with the Bible, but also bitter opposition from some philosophers and clerics, two of whom denounced him to the Roman Inquisition early in 1615, warning "that Galileo should not go outside mathematics and physics and should avoid provoking theologians by teaching them how to read the Bible". One of the philosophers who issued a complaint to the Inquisition was Tommaso Caccini, who also attacked Galileo in sermons, ordering him to withdraw from philosophy and citing Acts 1:10: "Ye men of Galilee, why stand ye gazing up into heaven?".
The report of the Inquisition's consultants declared heliocentrism as "false and contrary to Scripture" in February 1616. The Church demanded Galileo stop teaching and defending Copernican theory, to which Galileo agreed. That month, the Church's Congregation of the Index issued a decree suspending De revolutionibus until it could be "corrected." The edits to De revolutionibus, which omitted or altered nine sentences, were issued four years later, in 1620.
A second trial in 1633 led to Galileo's house arrest and a ban on his books.
"In its extrascientific consequences," writes science historian Thomas Kuhn, "the Copernican theory is not typical: few scientific theories have played such a large role in non-scientific thought." The Copernican Revolution began as a narrowly technical revision of classical astronomy but ended by altering the Western World's relation to both the Universe and God. By reimagining the Earth not as the unique and focal center of GodâÂÂs creation and attention but instead as just an unremarkable planet, circulating purposelessly around an ordinary star, no different from an uncountable number of others, the Revolution became an enormous cultural upheaval that shattered the long-standing synthesis of Aristotelian physics and Christian theology. A Universe where the physical location of human beings had easily understood spiritual significance gave way to a cosmic scheme where human existence appeared neither unique nor privileged.
The end of the human-centered cosmos was eventually part of a complete replacement of a qualitative world by a quantitative one. That replacement appeared to leave human beings alone in a silent, infinite universe where existence was no longer a reflection of divine values but merely a neutral fact of mathematics. The science historian Alexandre Koyré memorably identified this unintended outcome - the stripping of hierarchical order, purpose and meaning from the universe â as the "utter devalorization of being." Stripping away the religious logic that had undergirded Western culture up to Copernicus, the Revolution forced a significant fraction of humanity to find alternative sources for identity and meaning, a transition which is arguably still ongoing.
In The Structure of Scientific Revolutions, Kuhn characterized the Copernican Revolution as the first historical example of a paradigm shift in science:
Kuhn acknowledged that Copernicus' work De revolutionibus was not itself revolutionary:
Herbert Butterfield, Arthur Koestler, Otto Neugebauer and David Wootton, have all, to a greater or lesser extent, disagreed with Kuhn about how revolutionary Copernicus' work should be considered.
Years after The Structure of Scientific Revolutions, Kuhn replaced the idea of paradigm shift with the idea that scientific language is a taxonomy and that a scientific revolution is essentially a restructuring of taxonomic categories. He adopted the model of the biological process of speciation to describe the birth of a new scientific specialty: <blockquote>[R]evolutions, which produce new divisions between fields in scientific development, are much like episodes of speciation in biological evolution. The biological parallel to revolutionary change is not mutation, as I thought for many years, but speciation. And the problems presented by speciation (e.g., the difficulty in identifying an episode of speciation until some time after it has occurred, and the impossibility even then, of dating the time of its occurrence) are very similar to those presented by revolutionary change and by the emergence and individuation of new scientific specialties.</blockquote>
Immanuel Kant in his Critique of Pure Reason (1787 edition) drew a parallel between the Copernican hypothesis and the epistemology of his new transcendental philosophy. Kant's comparison is made in the Preface to the second edition of the Critique of Pure Reason (published in 1787; a heavy revision of the first edition of 1781). Kant argues that, just as Copernicus moved from the supposition of heavenly bodies revolving around a stationary spectator to a moving spectator, so metaphysics, "proceeding precisely on the lines of Copernicus' primary hypothesis", should move from assuming that "knowledge must conform to objects" to the supposition that "objects must conform to our [a priori] knowledge". Scholars have argued that Kant's analogy is flawed, however, because it essentially reverses Copernicus' logic. Tom Rockmore also notes Kant himself never used the specific phrase.
Following Kant, the phrase "Copernican Revolution" in the 20th century came to be used as a metaphor for intellectual upheaval.