Copernican Revolution


In the 16th century, Nicolaus Copernicus proposed a major shift in the understanding of the cycle of the heavenly spheres. Driven by a desire for a more perfect description of the cosmos than the prevailing Ptolemaic model - which posited that the Sun circled a stationary Earth - Copernicus instead advanced a heliostatic system where a stationary Sun was located near, though not precisely at, the mathematical center of the heavens. In the 20th century, the science historian Thomas Kuhn characterized the "Copernican Revolution" as the first historical example of a paradigm shift in human knowledge. Herbert Butterfield, Arthur Koestler and David Wootton, on the other hand, all disagreed with Kuhn about how revolutionary Copernicus' work should be considered.

Heliocentrism

Before Copernicus

The "Copernican Revolution" is named for Nicolaus Copernicus, whose Commentariolus, written before 1514, was the first explicit presentation of the heliocentric model in Renaissance scholarship.
The idea of heliocentrism is much older; it can be traced 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 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 described a heliocentric model. John Scotus Eriugena 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 Persian school of astronomy associated with the
Maragheh observatory.
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.

Nicolaus Copernicus

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 and to have performed observations of lunar motions on 9 March 1497. Copernicus went on to develop an explicitly heliocentric model of planetary motion, at first written in his short work Commentariolus some time before 1514, circulated in a limited number of copies among his acquaintances. He continued to refine his system until publishing his larger work, De revolutionibus orbium coelestium, which contains detailed diagrams and tables.
The Copernican model makes the claim of describing the physical reality of the cosmos, something which the Ptolemaic model was no longer believed to be able to provide. Copernicus removed Earth from the center of the universe, set the heavenly bodies in rotation around the Sun, and introduced Earth's daily rotation on its axis. While Copernicus's work sparked the "Copernican Revolution", it did not mark its end. In fact, Copernicus's own system had multiple shortcomings that would have to be amended by later astronomers and led to our current understanding of astronomy.
Copernicus did not only come up with a theory regarding the nature of the Sun in relation to the Earth, but thoroughly worked to debunk some of the minor details within the geocentric theory. In his article about heliocentrism as a model, author Owen Gingerich writes that in order to persuade people of the accuracy of his model, Copernicus created a mechanism in order to return the description of celestial motion to a “pure combination of circles.”

Reception

16th Century Astronomers

In The Sleepwalkers, 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:

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.

Tycho Brahe

was a Danish nobleman who was well known as an astronomer in his time. Further advancement in the understanding of the cosmos would require new, more accurate observations than those that Nicolaus Copernicus relied on, and Tycho made great strides in this area. Tycho formulated a geoheliocentrism, meaning the Sun moved around the Earth while the planets orbited the Sun, known as the Tychonic system. Although Tycho appreciated the advantages of Copernicus's system, he like many others could not accept the movement of the Earth.
In 1572, Tycho Brahe observed a new star in the constellation Cassiopeia. For eighteen months, it shone brightly in the sky with no visible parallax, indicating it was part of the heavenly region of stars according to Aristotle's model. However, according to that model, no change could take place in the heavens so Tycho's observation was a major discredit to Aristotle's theories. In 1577, Tycho observed a great comet in the sky. Based on his parallax observations, the comet passed through the region of the planets. According to Aristotelian theory, only uniform circular motion on solid spheres existed in this region, making it impossible for a comet to enter this region. Tycho concluded there were no such spheres, raising the question of what kept a planet in orbit.
With the patronage of the King of Denmark, Tycho Brahe established Uraniborg, an observatory in Hven. For 20 years, Tycho and his team of astronomers compiled astronomical observations that were vastly more accurate than those made before. These observations would prove vital in future astronomical breakthroughs.

Johannes Kepler

Kepler found employment as an assistant to Tycho Brahe and, upon Brahe's unexpected death, replaced him as imperial mathematician of Emperor Rudolph II. He was then able to use Brahe's extensive observations to make remarkable breakthroughs in astronomy, such as the three laws of planetary motion. Kepler would not have been able to produce his laws without the observations of Tycho, because they allowed Kepler to prove that planets traveled in ellipses, and that the Sun does not sit directly in the center of an orbit but at a focus. Galileo Galilei came after Kepler and developed his own telescope with enough magnification to allow him to study Venus and discover that it has phases like a moon. The discovery of the phases of Venus was one of the more influential reasons for the transition from geocentrism to heliocentrism. Sir Isaac Newton's Philosophiæ Naturalis Principia Mathematica concluded the Copernican Revolution. The development of his laws of planetary motion and universal gravitation explained the presumed motion related to the heavens by asserting a gravitational force of attraction between two objects.
In 1596, Kepler published his first book, the Mysterium Cosmographicum, which was the second to endorse Copernican cosmology by an astronomer since 1540. The book described his model that used Pythagorean mathematics and the five Platonic solids to explain the number of planets, their proportions, and their order. The book garnered enough respect from Tycho Brahe to invite Kepler to Prague and serve as his assistant.
In 1600, Kepler set to work on the orbit of Mars, the second most eccentric of the six planets known at that time. This work was the basis of his next book, the Astronomia nova, which he published in 1609. The book argued heliocentrism and ellipses for planetary orbits instead of circles modified by epicycles. This book contains the first two of his eponymous three laws of planetary motion. In 1619, Kepler published his third and final law which determined the relation between orbital period and orbital path of planets.
Kepler's work in astronomy was new in part. Unlike those who came before him, he discarded the assumption that planets moved in a uniform circular motion, replacing it with elliptical motion. Also, like Copernicus, he asserted the physical reality of a heliocentric model as opposed to a geocentric one. Yet, despite all of his breakthroughs, Kepler could not explain the physics that would keep a planet in its elliptical orbit.

Kepler's laws of planetary motion

Galileo Galilei

Galileo Galilei was an Italian scientist who is sometimes referred to as the "father of modern observational astronomy". 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 30× 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.

Sphere of the fixed stars

In the sixteenth century, a number of writers inspired by Copernicus, such as Thomas Digges, Giordano Bruno and William Gilbert argued for an indefinitely extended or even infinite universe, with other stars as distant suns. This contrasts with the Aristotelian view of a sphere of the fixed stars. Although opposed by Copernicus and Kepler, in 1610 Galileo made his telescopic observation of the faint strip of the Milky Way, which he found it resolves in innumerable white star-like spots, presumably farther stars themselves. By the middle of the 17th century, this new view became widely accepted, partly due to the support of René Descartes.

Isaac Newton

Newton was a well known English physicist and mathematician who was known for his book Philosophiæ Naturalis Principia Mathematica. He was a main figure in the Scientific Revolution for his laws of motion and universal gravitation. The laws of Newton are said to be the ending point of the Copernican Revolution.
Newton used Kepler's laws of planetary motion to derive his law of universal gravitation. Newton's law of universal gravitation was the first law he developed and proposed in his book Principia. The law states that any two objects exert a gravitational force of attraction on each other. The magnitude of the force is proportional to the product of the gravitational masses of the objects, and inversely proportional to the square of the distance between them. Along with Newton's law of universal gravitation, the Principia also presents his three laws of motion. These three laws explain inertia, acceleration, action and reaction when a net force is applied to an object.

Metaphorical usage

Immanuel Kant

in his Critique of Pure Reason 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. 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 knowledge".
Much has been said on what Kant meant by referring to his philosophy as "proceeding precisely on the lines of Copernicus' primary hypothesis". There has been a long-standing discussion on the appropriateness of Kant's analogy because, as most commentators see it, Kant inverted Copernicus's primary move.
According to Tom Rockmore, Kant himself never used the "Copernican revolution" phrase about himself, though it was "routinely" applied to his work by others.

After Kant

Following Kant, the phrase "Copernican Revolution" in the 20th century came to be used for any paradigm shift, for example in reference to Freudian psychoanalysis or continental philosophy and analytic linguistic philosophy.

Works cited

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