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Copernicus’ revolution and Galileo’s vision: our changing view of the universe in pictures

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It’s not a stretch to say the Copernican revolution fundamentally changed the way we think about our place in the universe. In antiquity people believed the Earth was the centre of the solar system and the universe, whereas now we know we are on just one of many planets orbiting the sun.

But this shift in view didn’t happen overnight. Rather, it took almost a century of new theory and careful observations, often using simple mathematics and rudimentary instruments, to reveal our true position in the heavens.

We can gain insights into how this profound shift unfolded by looking at the actual notes left by the astronomers who contributed to it. These notes give us a clue to the labour, insights and genius that drove the Copernican revolution.

Wandering stars

Imagine you’re an astronomer from antiquity, exploring the night sky without the aid of a telescope. At first the planets don’t really distinguish themselves from the stars. They’re a bit brighter than most stars and twinkle less, but otherwise look like stars.

In antiquity, what really distinguished planets from stars was their motion through the sky. From night to night, the planets gradually moved with respect to the stars. Indeed “planet” is derived from the Ancient Greek for “wandering star”.

And planetary motion isn’t simple. Planets appear to speed up and slow down as they cross the sky. Planets even temporarily reverse direction, exhibiting “ retrograde motion ”. How can this be explained?

Ptolemy epicycles

Ancient Greek astronomers produced geocentric (Earth-centred) models of the solar system, which reached their pinnacle with the work of Ptolemy . This model, from an Arabic copy of Ptolemy’s Almagest , is illustrated above.

Ptolemy explained planetary motion using the superposition of two circular motions, a large “ deferent ” circle combined with a smaller “ epicycle ” circle.

Furthermore, each planet’s deferent could be offset from the position of the Earth and the steady (angular) motion around the deferent could be defined using a position know as an equant , rather than the position of the Earth or the centre of the deferent. Got that?

It is rather complex. But, to his credit, Ptolemy’s model predicted the positions of planets in the night sky with an accuracy of a few degrees (sometimes better). And it thus became the primary means of explaining planetary motion for over a millennium.

Copernicus’ shift

In 1543, the year of his death, Nicolaus Copernicus started his eponymous revolution with the publication of De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres). Copernicus’ model for the solar system is heliocentric, with the planets circling the sun rather than Earth.

Perhaps the most elegant piece of the Copernican model is its natural explanation of the changing apparent motion of the planets. The retrograde motion of planets such as Mars is merely an illusion , caused by the Earth “overtaking” Mars as they both orbit the sun.

Ptolemaic baggage

Unfortunately, the original Copernican model was loaded the Ptolemaic baggage. The Copernican planets still travelled around the solar system using motions described by the superposition of circular motions. Copernicus disposed of the equant, which he despised , but replaced it with the mathematically equivalent epicyclet.

Astronomer-historian Owen Gingerich and his colleagues calculated planetary coordinates using Ptolemaic and Copernican models of the era, and found that both had comparable errors . In some cases the position of Mars is in error by 2 degrees or more (far larger than the diameter of the moon). Furthermore, the original Copernican model was no simpler than the earlier Ptolemaic model.

As 16th Century astronomers did not have access to telescopes, Newtonian physics, and statistics, it wasn’t obvious to them that the Copernican model was superior to the Ptolemaic model, even though it correctly placed the sun in the centre of the solar system.

Along comes Galileo

From 1609, Galileo Galilei used the recently invented telescope to observe the sun, moon and planets. He saw the mountains and craters of the moon, and for the first time revealed the planets to be worlds in their own right. Galileo also provided strong observational evidence that planets orbited the sun.

Galileo’s observations of Venus were particularly compelling. In Ptolemaic models, Venus remains between the Earth and the sun at all times, so we should mostly view the night side of Venus. But Galileo was able to observe the day-lit side of Venus, indicating that Venus can be on the opposite side of the sun from the Earth.

Kepler’s war with Mars

The circular motions of Ptolemaic and Copernican models resulted in large errors, particularly for Mars, whose predicted position could be in error by several degrees. Johannes Kepler devoted years of his life to understanding the motion of Mars, and he cracked this problem with a most ingenious weapon.

Planets (approximately) repeat the same path as they orbit the sun, so they return to the same position in space once every orbital period. For example, Mars returns to the same position in its orbit every 687 days.

As Kepler knew the dates when a planet would be at the same position in space, he could use the different positions of the Earth along its own orbit to triangulate the planets’ positions, as illustrated above. Kepler, using astronomer Tycho Brahe’s pre-telescopic observations , was able to trace out the elliptical paths of the planets as they orbited the sun.

This allowed Kepler to formulate his three laws of planetary motion and predict planetary positions with far greater precision than previously possible. He thus laid the groundwork for the Newtonian physics of the late 17th century, and the remarkable science that followed.

Kepler himself captured the new world view and its broader significance in 1609’s Astronomia nova (New Astronomy):

To me, however the truth is more pious still, and (with all due respect to the Doctors of the Church) I prove philosophically not only that the earth is round, not only that it is inhabited all the way around at the antipodes, not only that is it contemptibly small, but also that it is carried along among the stars.

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The Copernican Revolution Essay

Introduction, reasons for accepting the copernican theory, comparing the heliocentric and ptolemaic theories, the tychonic theory, works cited.

Modern science can be said to have its roots from the Copernican theory, though it was received with uncertainty by the Copernicans prior to the seventeenth century (Curd 3). Most of the scientists in the sixteenth century believe Ptolemy’s theory of Earth-centered astronomy, as well as Tycho Brahe’s theory of Geoheliocentric system. The reluctance of early scientists in accepting the Copernican theory makes their later approval raise a few questions about the other theories (Curd 3).

One big question posed by this shift of mind is why and when the Copernican theory gained approval over the Ptolemaic theory. Current reviews of the ideas previously adopted as explanations of the change of beliefs have been found to be unsatisfactory. The Copernican theory had been found to be more precise in its forecasts and clear-cut than the Ptolemaic, which is not the case today (Curd 3).

One of the reasons as to why the Copernican theory was accepted is that it satisfied the “taste” of people, who disregarded rationale and facts. This harsh conclusion by Thomas Kuhn was challenged by Zahar and Lakatos, who argued that the research undertaken for the Copernican programme was empirically precise (Curd 3). The empirical progression of the Copernican theory was based on its essential geometric configuration, which had adequate projecting capabilities.

Lakatos and Zahar later edited the conception of a novel fact, stating that it was not necessary for it to be unfamiliar, but it should not have been acknowledged in the formation of the theory (Curd 3). Glymour was also in support of the Copernican theory, compared to the Ptolemaic one, stating that the latter was objectively inferior. The superiority of the former theory was observed in its capability to validate and be analyzed by the facts of that time based on positional astronomy (Curd 4).

Support on the validity of the heliocentric theory has been from various scientists, like Millman and Hall, who found it satisfying before the discoveries by Newton and Galileo (Curd 4). The book on testing and confirmation of theories by Glymour looks at the two theories comparatively; that is the geocentric and the heliocentric theories.

Glymour and Zahar believe to have been contributors to the understanding of the heliocentric theory, in terms of its methodical logic, harmony and accord, as expressed by other authors like Rheticus, which is contrary to the belief that the theory was irrational, as put forward by Kuhn (Curd 4). One way to compare the two theories is by using the equation (1),

• 1/T p = 1/T e -+ 1/S p where T is the heliocentric period of planet P, Te is the heliocentric period of Earth and S is the time interval between successive episodes of retrograde motion as viewed from earth. When the planet is superior, the – sign in the equation is used, while + is used for an inferior planet (Curd 5).

Inferior planets are Mercury and Venus. The Copernican theory works with an excess of three planets on the superior side, while the Ptolemaic theory works with the superior planets only. The Ptolemaic theory also fails to explain the relationship between the motion of the planets and the solar component.

The Copernican theory offers various explanations unlike the Ptolemaic theory (Curd 5). One of the things enlightened by the Copernican theory is the progressively diminishing value of S, as the distance of the planet from earth increases, irrespective of the direction (Curd 5).

The limits of the Ptolemaic theory do not allow for the determination of the displacement of planets from earth. Aristotle defended one of the theories in the Ptolemaic theory that states that the period of a planet is proportional to the size of its orbit (Curd 6). In the heliocentric theory, the distances are obtained with reference to the distance between the planets and centre of revolution, which is actually the sun.

These displacements that are predetermined are used as a basis for the order assignments, which is an indication of harmony and order, characteristics of Copernican theory, and lacking in the Ptolemaic theory (Curd 6). Bases on the tests conducted between the two theories, the Copernican theory emerges as the better one with greater explanatory power. The tests were based on the same positional data (Curd 6).

The Copernican revolution was defined as the change of belief from the Ptolemaic theory to the Copernican theory. The revolution was dependent on two decisions namely the denunciation of the Ptolemaic theory as untrue, and the recognition of the Copernican theory as correct (Curd 6).

The prudence of either choice is not explained by the positional data due to the effect of two factors namely the Tychonic theory, a third alternative theory, and the existence of vital drawbacks to the Copernican theory. The Tychonic theory was published towards the end of the sixteenth century by Brahe. This theory suggests a geoheliocentric array whereby the earth is static and at the centre (Curd 6).

The sun and the planets are said to revolve around the earth. Therefore, the planets have the orbit of the sun as their deferent, and their major epicycle is the heliocentric orbits. Unlike the Ptolemaic theory, the Tychonic system is comparable to the Copernican theory, both kinematically and geometrically (Curd 6).

The Tychonic theory is like the Copernican theory in that in spite of its two centers of revolution, it provides for the derivation of equation 1, and the calculation of the displacement of the planets from the sun (Curd 7). The Copernican theory had two main problems namely the perceptible proof that the earth is static, and the lack of noticeable stellar parallax.

These problems were unique to the Copernican theory, since the other two theories were geostatic. The scientists in support of the Copernican theory argued that the two problems were contradicting with the requirements of the theory, which are two terrestrial motions. The writings of Galileo, in the early seventeenth century were sufficient to disregard the Ptolemaic theory, though the issues in the other two theories remained (Curd 7).

Semi-Tychonic systems appeared in the 16 th and 17 th centuries and believed that the earth rotated, but did not revolve around the sun (Curd 7). The semi- Tychonic theory was accepted since it enjoyed similar merits with those of the Copernican theory, as well as its simplicity, which made sure to ignore the independent motion of every celestial body. This was especially beneficial in its acceptance after the discovery of Newton’s first law of motion, which defines the forces that maintain a body in circular motion (Curd 7).

The acceptance of the Copernican theory was supported by both observation and acceptance on its scale of rationality as was seen in the Tychonic alternatives (Curd 8). One deduction observed in the determination of the validity of the theories is that the scientists who support the law focus a lot of their energy and time to build on it, and therefore defend it from harsh criticism, and non-believers (Curd 8). The justification of any theory is only dependent on scientific analysis, to solve any mysterious questions and doubt in people (Curd 8).

Curd, Martin V. “The Rationality of the Copernican Revolution.” PSA: Proceedings of the Biennial Meeting of the Philosophy of Science Association (1982): 1, 3-13.

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IvyPanda. (2019, December 2). The Copernican Revolution. https://ivypanda.com/essays/the-copernican-revolution/

"The Copernican Revolution." IvyPanda , 2 Dec. 2019, ivypanda.com/essays/the-copernican-revolution/.

IvyPanda . (2019) 'The Copernican Revolution'. 2 December.

IvyPanda . 2019. "The Copernican Revolution." December 2, 2019. https://ivypanda.com/essays/the-copernican-revolution/.

1. IvyPanda . "The Copernican Revolution." December 2, 2019. https://ivypanda.com/essays/the-copernican-revolution/.

Bibliography

IvyPanda . "The Copernican Revolution." December 2, 2019. https://ivypanda.com/essays/the-copernican-revolution/.

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Nicolaus Copernicus

By: History.com Editors

Updated: January 31, 2023 | Original: November 9, 2009

Nicolaus Copernicus was a Polish astronomer and mathematician known as the father of modern astronomy. He was the first European scientist to propose that Earth and other planets revolve around the sun, the heliocentric theory of the solar system. Prior to the publication of his major astronomical work, “On the Revolutions of the Heavenly Spheres,” in 1543, European astronomers argued that Earth lay at the center of the universe, the view also held by most ancient philosophers. In addition to correctly postulating the order of the known planets from the sun and estimating their orbital periods relatively accurately, Copernicus argued that Earth turned daily on its axis and that gradual shifts of this axis accounted for the changing seasons.

Who Was Copernicus?

Nicolaus Copernicus was born on February 19, 1473 in Torun, a city in north-central Poland on the Vistula River. Copernicus was born into a family of well-to-do merchants, and after his father’s death, his uncle–soon to be a bishop–took the boy under his wing. He was given the best education of the day and bred for a career in canon (church) law.

At the University of Krakow (today’s Jagiellonian University ), he studied liberal arts, including astronomy and astrology, and then, like many Europeans of his social class, was sent to Italy to study medicine and law.

While studying at the University of Bologna , he lived for a time in the home of Domenico Maria de Novara, the principal astronomer at the university. Astronomy and astrology were at the time closely related and equally regarded, and Novara had the responsibility of issuing astrological prognostications for Bologna.

Copernicus sometimes assisted him in his observations, and Novara exposed him to criticisms both of astrology and of aspects of the Ptolemaic system — founded by the ancient mathematician and astronomer Ptolemy — which placed Earth at the center of the universe.

Copernicus later studied at the University of Padua and in 1503 received a doctorate in canon law from the University of Ferrara . He returned to Poland, where he became a church administrator and doctor.

In his free time, he dedicated himself to scholarly pursuits, which sometimes included astronomical work. By 1514, his reputation as a learned mathematician, physician and astronomer was such that he was consulted on matters of currency and coinage, and by church leaders attempting to reform the Julian calendar .

Ptolemaic System

The cosmology of early 16th-century Europe held that Earth sat stationary and motionless at the center of several rotating, concentric spheres that bore the celestial bodies: the sun, the moon, the known planets, and the stars.

From ancient times, philosophers adhered to the belief that the heavens were arranged in circles (which by definition are perfectly round), causing confusion among astronomers who recorded the often eccentric motion of the planets, which sometimes appeared to halt in their orbit of Earth and move retrograde across the sky.

In the second century, Ptolemy sought to resolve this problem by arguing that the sun, planets, and moon move in small circles around much larger circles that revolve around Earth. These small circles he called epicycles, and by incorporating numerous epicycles rotating at varying speeds he made his celestial system correspond with most astronomical observations on record.

The Ptolemaic system remained Europe’s accepted cosmology for more than 1,000 years, but by Copernicus’ day accumulated astronomical evidence had thrown some of his theories into confusion. Astronomers disagreed on the order of the planets from Earth, and it was this problem that Copernicus addressed at the beginning of the 16th century.

Heliocentric Theory

Sometime between 1508 and 1514, Copernicus wrote a short astronomical treatise commonly called the Commentariolus, or “Little Commentary,” which laid the basis for his sun-centered or heliocentric theory, a radical departure from the conventional wisdom of his era. The work was not published in his lifetime.

In the treatise, he correctly postulated the order of the known planets, including Earth, from the sun, and estimated their orbital periods relatively accurately.

For Copernicus, his heliocentric theory was by no means a watershed, for it created as many problems as it solved. For instance, heavy objects were always assumed to fall to the ground because Earth was the center of the universe. Why would they do so in a sun-centered system?

He retained the ancient belief that circles governed the heavens, but his evidence showed that even in a sun-centered universe the planets and stars did not revolve around the sun in perfectly circular orbits.

Because of these problems and others, Copernicus delayed publication of his major astronomical work, De revolutionibus orbium coelestium libri vi, or “On the Revolutions of the Heavenly Spheres,” nearly all his life. Completed around 1530, it was not published until 1543 — the year of his death.

What Did Nicolaus Copernicus Discover?

In “On the Revolutions of the Heavenly Spheres,” Copernicus’ groundbreaking argument that Earth and the planets revolve around the sun led him to make a number of other major astronomical discoveries. While revolving around the sun, Earth, he argued, spins on its axis daily. Earth takes one year to orbit the sun and during this time wobbles gradually on its axis, which accounts for the precession of the equinoxes.

Major flaws in the work include his concept of the sun as the center of the whole universe, not just the solar system, and his failure to grasp the reality of elliptical orbits, which forced him to incorporate numerous epicycles into his system, as did Ptolemy. With no concept of gravity, Earth and the planets still revolved around the sun on giant transparent spheres.

In his dedication to “On the Revolutions of the Heavenly Spheres”–an extremely dense scientific work–Copernicus noted that “mathematics is written for mathematicians.” If the work were more accessible, many would have objected to its non-biblical and hence heretical concept of the universe.

For decades, “On the Revolutions of the Heavenly Spheres” remained unknown to all but the most sophisticated astronomers, and most of these men, while admiring some of Copernicus’ arguments, rejected his heliocentric basis.

Death and Legacy

Nicolaus Copernicus died on May 24, 1543 in what is now Frombork, Poland. Largely unknown outside of academic circles, he died the year his major work was published, saving him from the outrage of some religious leaders who later condemned his heliocentric view of the universe as heresy.

One of those critics was Martin Luther , the infamous Vatican critic who was one of the founders of the Reformation . Luther stated that “This fool wishes to reverse the entire science of astronomy; but sacred Scripture tells us that Joshua commanded the Sun to stand still, and not the Earth.” The Vatican did eventually ban “On the Revolutions of the Heavenly Spheres” in 1616.

It was not until the early 17th century that Galileo and Johannes Kepler developed and popularized the Copernican theory, which for Galileo resulted in a trial and conviction for heresy. Following Isaac Newton ’s work in celestial mechanics in the late 17th century, acceptance of the Copernican theory spread rapidly in non-Catholic countries, and by the late 18th century the Copernican view of the solar system was almost universally accepted.

Centuries after his burial in an unmarked grave beneath the floor of the cathedral in Frombork, Copernicus’ remains were finally given a hero’s burial in 2010. His body was identified using DNA analysis of the skull, which matched the DNA found in hairs that were tucked in the pages of books that Copernicus owned.

His black granite tombstone is now marked with a heliocentric model of the solar system featuring a golden sun encircled by six of the planets.

Nicolaus Copernicus. Stanford Encyclopedia of Philosophy, Stanford University . Nicolaus Copernicus biography: Facts & discoveries. Space.com . Vatican bans Copernicus' book. Physics Today . 16th-century astronomer Copernicus reburied as hero in Poland. Associated Press .

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Nicolaus Copernicus

Nicolaus Copernicus (1473–1543) was a mathematician and astronomer who proposed that the sun was stationary in the center of the universe and the earth revolved around it. Disturbed by the failure of Ptolemy’s geocentric model of the universe to follow Aristotle’s requirement for the uniform circular motion of all celestial bodies. Copernicus decided that he could achieve his goal only through a heliocentric model. He thereby created a concept of a universe in which the distances of the planets from the sun bore a direct relationship to the size of their orbits. At the time Copernicus’s heliocentric idea was very controversial; nevertheless, it was the start of a change in the way the world was viewed, and Copernicus came to be seen as the initiator of what is commonly known as the Scientific Revolution.

1. Life and Works

2.1 pre-copernican astronomy, 2.2 the commentariolus, 2.3 on the revolutions, 2.4 rheticus and the narratio prima, 2.5 printing on the revolutions and osiander’s preface, 2.6 sixteenth century reactions to on the revolutions, a. complete works of copernicus, b. other translations of copernicus’s works, c. translations of other primary sources, d. secondary sources, other internet resources, related entries.

Nicolaus Copernicus was born on 19 February 1473, the youngest of four children of Nicolaus Copernicus, Sr., a well-to-do merchant who had moved to Torun from Cracow, and Barbara Watzenrode, the daughter of a leading merchant family in Torun. The city, on the Vistula River, had been an important inland port in the Hanseatic League. However, fighting between the Order of the Teutonic Knights and the Prussian Union in alliance with the Kingdom of Poland ended in 1466, and West Prussia, which included Torun, was ceded to Poland, and Torun was declared a free city of the Polish kingdom. Thus the child of a German family was a subject of the Polish crown.

The father died in 1483, and the children’s maternal uncle, Lucas Watzenrode (1447–1512), took them under his protection. Watzenrode was a very successful cleric – he was to become bishop of Warmia (Ermland in German) in 1489 – and he both facilitated his nephew’s advancement in the church and directed his education. In 1491 Copernicus enrolled in the University of Cracow. There is no record of his having obtained a degree, which was not unusual at the time as he did not need a bachelor’s degree for his ecclesiastical career or even to study for a higher degree. But the University of Cracow offered courses in mathematics, astronomy, and astrology (see Goddu 25–33 on all the university offerings), and Copernicus’s interest was sparked, which is attested to by his acquisition of books in these subjects while at Cracow. [ 1 ]

In 1495 Watzenrode arranged Copernicus’s election as canon of the chapter of Frombork (Frauenberg in German) of the Cathedral Chapter of Warmia, an administrative position just below that of bishop. He assumed the post two years later, and his financial situation was secure for life. In the meantime, following in his uncle’s footsteps, Copernicus went to the University of Bologna in 1496 to study canon law (see Goddu part 2 on what Copernicus may have encountered in Italy). While at Bologna he lived with the astronomy professor Domenico Maria Novara and made his first astronomical observations. In addition, as Rosen (1971, 323) noted, “In establishing close contact with Novara, Copernicus met, perhaps for the first time in his life, a mind that dared to challenge the authority of [Ptolemy] the most eminent ancient writer in his chosen fields of study.” Copernicus also gave a lecture on mathematics in Rome, which may have focused on astronomy.

Copernicus’s studies at Bologna provided an advantage he did not have at Cracow – a teacher of Greek. Humanism began to infiltrate the Italian universities in the fifteenth century. As Grendler (510) remarked, “By the last quarter of the century, practically all universities had one or several humanists, many of them major scholars.” Antonio Cortesi Urceo, called Codro, became professor at Bologna in 1482 and added Greek several years later. Copernicus may have studied with him, for Copernicus translated into Latin the letters of the seventh-century Byzantine author Theophylactus Simocatta ( MW 27–71) from the 1499 edition of a collection of Greek letters produced by the Venetian humanist printer Aldus Manutius. Aldus had dedicated his edition to Urceo. Copernicus had his translation printed in 1509, his only publication prior to the On the Revolutions ( De revolutionibus ). It is important to note that Copernicus’s acquisition of a good reading knowledge of Greek was critical for his studies in astronomy because major works by Greek astronomers, including Ptolemy, had not yet been translated into Latin, the language of the universities at the time.

Copernicus left Bologna for Frombork in 1501 without having obtained his degree. The chapter then approved another leave of absence for Copernicus to study medicine at the University of Padua. The medical curriculum did not just include medicine, anatomy, and the like when Copernicus studied it. Siraisi (1990, 16) noted that “the reception in twelfth-century western Europe of Greek and Islamic technical astronomy and astrology fostered the development of medical astrology…the actual practice of medical astrology was greatest in the West between the fourteenth and the sixteenth centuries.” Astrology was taught in the medical schools of Italy. “The importance attached to the study of the stars in medieval medical education derived from a general and widely held belief that the heavenly bodies play an intermediary role in the creation of things here below and continue to influence them throughout their existence. The actual uses of astrology in medical diagnosis and treatment by learned physicians were many and various. ‘Astrological medicine’ is a vague and unsatisfactory term that can embrace any or all of the following: first, to pay attention to the supposed effect of astrological birth signs or signs at conception on the constitution and character of one’s patients; second, to vary treatment according to various celestial conditions…third, to connect the doctrine of critical days in illness with astrological features, usually phases of the moon; and fourth, to predict or explain epidemics with reference to planetary conjunctions, the appearance of comets, or weather conditions” (Siraisi 1981, 141–42). It is true that astrology required that medical students acquire some grounding in astronomy; nevertheless, it is likely that Copernicus studied astrology while at the University of Padua. [ 2 ]

Copernicus did not receive his medical degree from Padua; the degree would have taken three years, and Copernicus had only been granted a two-year leave of absence by his chapter. Instead he matriculated in the University of Ferrara, from which he obtained a doctorate in canon law. But he did not return to his chapter in Frombork; rather he went to live with his uncle in the episcopal palace in Lidzbark-Warminski (Heilsberg in German). Although he made some astronomical observations, he was immersed in church politics, and after his elderly uncle became ill in 1507, Copernicus was his attending physician. Rosen (1971, 334–35) reasonably conjectured that the bishop may have hoped that his nephew would be his successor, but Copernicus left his uncle because his duties in Lidzbark-Warminski interfered with his continuing pursuit of his studies in astronomy. He took up residence in his chapter of Frombork in 1510 and stayed there the rest of his life.

Not that leaving his uncle and moving to Frombork exempted Copernicus from continued involvement in administrative and political duties. He was responsible for the administration of various holdings, which involved heading the provisioning fund, adjudicating disputes, attending meetings, and keeping accounts and records. In response to the problem he found with the local currency, he drafted an essay on coinage ( MW 176–215) in which he deplored the debasement of the currency and made recommendations for reform. His manuscripts were consulted by the leaders of both Prussia and Poland in their attempts to stabilize the currency. He was a leader for West Prussia in the war against the Teutonic Knights, which lasted from 1520–1525. He was physician for the bishop (his uncle had died in 1512) and members of the chapter, and he was consulting physician for notables in East and West Prussia.

Nevertheless, Copernicus began to work on astronomy on his own. Sometime between 1510 and 1514 he wrote an essay that has come to be known as the Commentariolus ( MW 75–126) that introduced his new cosmological idea, the heliocentric universe, and he sent copies to various astronomers. He continued making astronomical observations whenever he could, hampered by the poor position for observations in Frombork and his many pressing responsibilities as canon. Nevertheless, he kept working on his manuscript of On the Revolutions . He also wrote what is known as Letter against Werner ( MW 145–65) in 1524, a critique of Johann Werner’s “Letter concerning the Motion of the Eighth Sphere” ( De motu octavae sphaerae tractatus primus ). Copernicus claimed that Werner erred in his calculation of time and his belief that before Ptolemy the movement of the fixed stars was uniform, but Copernicus’s letter did not refer to his cosmological ideas.

In 1539 a young mathematician named Georg Joachim Rheticus (1514–1574) from the University of Wittenberg came to study with Copernicus. Rheticus brought Copernicus books in mathematics, in part to show Copernicus the quality of printing that was available in the German-speaking cities. He published an introduction to Copernicus’s ideas, the Narratio prima (First Report). Most importantly, he convinced Copernicus to publish On the Revolutions . Rheticus oversaw most of the printing of the book, and on 24 May 1543 Copernicus held a copy of the finished work on his deathbed.

2. Astronomical Ideas and Writings

Classical astronomy followed principles established by Aristotle. Aristotle accepted the idea that there were four physical elements – earth, water, air, and fire. He put the earth in the center of the universe and contended that these elements were below the moon, which was the closest celestial body. There were seven planets, or wandering stars, because they had a course through the zodiac in addition to traveling around the earth: the moon, Mercury, Venus, the sun, Mars, Jupiter. Beyond that were the fixed stars. The physical elements, according to Aristotle moved vertically, depending on their ‘heaviness’ or ‘gravity’; the celestial bodies were not physical but a ‘fifth element’ or ‘quintessence’ whose nature was to move in perfect circles around the earth, making a daily rotation. Aristotle envisioned the earth as the true center of all the circles or ‘orbs’ carrying the heavenly bodies around it and all motion as ‘uniform,’ that is, unchanging.

But observers realized that the heavenly bodies did not move as Aristotle postulated. The earth was not the true center of the orbits and the motion was not uniform. The most obvious problem was that the outer planets seemed to stop, move backwards in ‘retrograde’ motion for a while, and then continue forwards. By the second century, when Ptolemy compiled his Almagest (this common name of Ptolemy’s Syntaxis was derived from its Arabic title), astronomers had developed the concept that the orbit moves in ‘epicycles’ around a ‘deferrent,’ that is, they move like a flat heliacal coil around a circle around the earth. The earth was also off-center, on an ‘eccentric,’ as the heavenly bodies moved around a central point. Ptolemy added a point on a straight line opposite the eccentric, which is called the ‘equalizing point’ or the ‘equant,’ and around this point the heavenly bodies moved uniformly. Moreover, unlike the Aristotelian model, Ptolemy’s Almagest did not describe a unified universe. The ancient astronomers who followed Ptolemy, however, were not concerned if his system did not describe the ‘true’ motions of the heavenly bodies; their concern was to ‘save the phenomena,’ that is, give a close approximation of where the heavenly bodies would be at a given point in time. And in an age without professional astronomers, let alone the telescope, Ptolemy did a good job plotting the courses of the heavenly bodies.

Not all Greek astronomical ideas followed this geocentric system. Pythagoreans suggested that the earth moved around a central fire (not the sun). Archimedes wrote that Aristarchus of Samos actually proposed that the earth rotated daily and revolved around the sun. [ 3 ]

During the European Middle Ages, the Islamic world was the center of astronomical thought and activity. During the ninth century several aspects of Ptolemy’s solar theory were recalculated. Ibn al-Haytham in the tenth-eleventh century wrote a scathing critique of Ptolemy’s work: “Ptolemy assumed an arrangement that cannot exist, and the fact that this arrangement produces in his imagination the motions that belong to the planets does not free him from the error he committed in his assumed arrangement, for the existing motions of the planets cannot be the result of an arrangement that is impossible to exist” (quoted in Rosen 1984, 174). Swerdlow and Neugebauer (46–48) stressed that the thirteenth-century Maragha school was also important in finding errors and correcting Ptolemy: “The method of the Maragha planetary models was to break up the equant motion in Ptolemy’s models into two or more components of uniform circular motion, physically the uniform rotation of spheres, that together control the direction and distance of the center of the epicycle, so that it comes to lie in nearly the same position it would have in Ptolemy’s model, and always moves uniformly with respect to the equant.” They found that Copernicus used devices that had been developed by the Maragha astronomers Nasir al-Din Tusi (1201–1274), Muayyad al-Din al-Urdi (d. 1266), Qutb al-Din al-Shirazi (1236–1311), and Ibn al-Shatir (1304–1375). In addition, Ragep, 2005, has shown that a theory for the inner planets presented by Regiomontanus that enabled Copernicus to convert the planets to eccentric models had been developed by the fifteenth-century, Samarqand-trained astronomer ali Qushji (1403–1474). [ 4 ]

Renaissance humanism did not necessarily promote natural philosophy, but its emphasis on mastery of classical languages and texts had the side effect of promoting the sciences. Georg Peurbach (1423–1461) and (Johannes Müller) Regiomontanus (1436–1476) studied Greek for the purpose of producing an outline of Ptolemaic astronomy. By the time Regiomontanus finished the work in 1463, it was an important commentary on the Almagest as well, pointing out, for example, that Ptolemy’s lunar theory did not accord with observations. He noted that Ptolemy showed the moon to be at various times twice as far from the earth as at other times, which should make the moon appear twice as big. At the time, moreover, there was active debate over Ptolemy’s deviations from Aristotle’s requirement of uniform circular motion.

It is impossible to date when Copernicus first began to espouse the heliocentric theory. Had he done so during his lecture in Rome, such a radical theory would have occasioned comment, but there was none, so it is likely that he adopted this theory after 1500. Further, Corvinus, who helped him print his Latin translation in 1508–09, expressed admiration for his knowledge of astronomy, so that Copernicus’s concept may have still been traditional at this point. His first heliocentric writing was his Commentariolus . It was a small manuscript that was circulated but never printed. We do not know when he wrote this, but a professor in Cracow cataloged his books in 1514 and made reference to a “manuscript of six leaves expounding the theory of an author who asserts that the earth moves while the sun stands still” (Rosen, 1971, 343; MW 75). Thus, Copernicus probably adopted the heliocentric theory sometime between 1508 and 1514. Rosen (1971, 345) suggested that Copernicus’s “interest in determining planetary positions in 1512–1514 may reasonably be linked with his decisions to leave his uncle’s episcopal palace in 1510 and to build his own outdoor observatory in 1513.” In other words, it was the result of a period of intense concentration on cosmology that was facilitated by his leaving his uncle and the attendant focus on church politics and medicine.

It is impossible to know exactly why Copernicus began to espouse the heliocentric cosmology. Despite his importance in the history of philosophy, there is a paucity of primary sources on Copernicus. His only astronomical writings were the Commentariolus , the Letter against Werner , and On the Revolutions ; he published his translation of Theophylactus’s letters and wrote the various versions of his treatise on coinage; other writings relate to diocesan business, as do most of the few letters that survive. Sadly, the biography by Rheticus, which should have provided scholars with an enormous amount of information, has been lost. Therefore, many of the answers to the most interesting questions about Copernicus’s ideas and works have been the result of conjecture and inference, and we can only guess why Copernicus adopted the heliocentric system.

Most scholars believe that the reason Copernicus rejected Ptolemaic cosmology was because of Ptolemy’s equant. [ 5 ] They assume this because of what Copernicus wrote in the Commentariolus :

Yet the widespread [planetary theories], advanced by Ptolemy and most other [astronomers], although consistent with the numerical [data], seemed likewise to present no small difficulty. For these theories were not adequate unless they also conceived certain equalizing circles, which made the planet appear to move at all times with uniform velocity neither on its deferent sphere nor about its own [epicycle’s] center…Therefore, having become aware of these [defects], I often considered whether there could perhaps be found a more reasonable arrangement of circles, from which every apparent irregularity would be derived while everything in itself would move uniformly, as is required by the rule of perfect motion. ( MW 81).

Goddu (381–84) has plausibly maintained that while the initial motivation for Copernicus was dissatisfaction with the equant, that dissatisfaction may have impelled him to observe other violations of uniform circular motion, and those observations, not the rejection of the equant by itself, led to the heliocentric theory. Blumenberg (254) has pointed out that the mobility of the earth may have been reinforced by the similarity of its spherical shape to those of the heavenly bodies.

As the rejection of the equant suggests a return to the Aristotelian demand for true uniform circular motion of the heavenly bodies, it is unlikely that Copernicus adopted the heliocentric model because philosophies popular among Renaissance humanists like Neoplatonism and Hermetism compelled him in that direction. [ 6 ] Nor should we attribute Copernicus’s desire for uniform circular motions to an aesthetic need, for this idea was philosophical not aesthetic, and Copernicus’s replacing the equant with epicyclets made his system more complex than Ptolemy’s. Most importantly, we should bear in mind what Swerdlow and Neugebauer (59) asserted:

Copernicus arrived at the heliocentric theory by a careful analysis of planetary models – and as far as is known, he was the only person of his age to do so – and if he chose to adopt it, he did so on the basis of an equally careful analysis.

In the Commentariolus Copernicus listed assumptions that he believed solved the problems of ancient astronomy. Bardi has suggested that these assumptions are non-Euclidean axioms. Copernicus stated that the earth is only the center of gravity and center of the moon’s orbit; that all the spheres encircle the sun, which is close to the center of the universe; that the universe is much larger than previously assumed, and the earth’s distance to the sun is a small fraction of the size of the universe; that the apparent motion of the heavens and the sun is created by the motion of the earth; and that the apparent retrograde motion of the planets is created by the earth’s motion. Although the Copernican model maintained epicycles moving along the deferrent, which explained retrograde motion in the Ptolemaic model, Copernicus correctly explained that the retrograde motion of the planets was only apparent not real, and its appearance was due to the fact that the observers were not at rest in the center. The work dealt very briefly with the order of the planets (Mercury, Venus, earth, Mars, Jupiter, and Saturn, the only planets that could be observed with the naked eye), the triple motion of the earth (the daily rotation, the annual revolution of its center, and the annual revolution of its inclination) that causes the sun to seem to be in motion, the motions of the equinoxes, the revolution of the moon around the earth, and the revolution of the five planets around the sun.

The Commentariolus was only intended as an introduction to Copernicus’s ideas, and he wrote “the mathematical demonstrations intended for my larger work should be omitted for brevity’s sake…” ( MW 82). In a sense it was an announcement of the greater work that Copernicus had begun. The Commentariolus was never published during Copernicus’s lifetime, but he sent manuscript copies to various astronomers and philosophers. He received some discouragement because the heliocentric system seemed to disagree with the Bible, but mostly he was encouraged. Although Copernicus’s involvement with official attempts to reform the calendar was limited to a no longer extant letter, that endeavor made a new, serious astronomical theory welcome. Fear of the reaction of ecclesiastical authorities was probably the least of the reasons why he delayed publishing his book. [ 7 ] The most important reasons for the delay was that the larger work required both astronomical observations and intricate mathematical proofs. His administrative duties certainly interfered with both the research and the writing. He was unable to make the regular observations that he needed and Frombork, which was often fogged in, was not a good place for those observations. Moreover, as Gingerich (1993, 37) pointed out,

[Copernicus] was far from the major international centers of printing that could profitably handle a book as large and technical as De revolutionibus . On the other [hand], his manuscript was still full of numerical inconsistencies, and he knew very well that he had not taken complete advantage of the opportunities that the heliocentric viewpoint offered…Furthermore, Copernicus was far from academic centers, thereby lacking the stimulation of technically trained colleagues with whom he could discuss his work.

The manuscript of On the Revolutions was basically complete when Rheticus came to visit him in 1539. The work comprised six books. The first book, the best known, discussed what came to be known as the Copernican theory and what is Copernicus’s most important contribution to astronomy, the heliocentric universe (although in Copernicus’s model, the sun is not truly in the center). Book 1 set out the order of the heavenly bodies about the sun: “[The sphere of the fixed stars] is followed by the first of the planets, Saturn, which completes its circuit in 30 years. After Saturn, Jupiter accomplishes its revolution in 12 years. The Mars revolves in 2 years. The annual revolution takes the series’ fourth place, which contains the earth…together with the lunar sphere as an epicycle. In the fifth place Venus returns in 9 months. Lastly, the sixth place is held by Mercury, which revolves in a period of 80 days” ( Revolutions , 21–22). This established a relationship between the order of the planets and their periods, and it made a unified system. This may be the most important argument in favor of the heliocentric model as Copernicus described it. [ 8 ] It was far superior to Ptolemy’s model, which had the planets revolving around the earth so that the sun, Mercury, and Venus all had the same annual revolution. In book 1 Copernicus also insisted that the movements of all bodies must be circular and uniform, and noted that the reason they may appear nonuniform to us is “either that their circles have poles different [from the earth’s] or that the earth is not at the center of the circles on which they revolve” ( Revolutions , 11). Particularly notable for Copernicus was that in Ptolemy’s model the sun, the moon, and the five planets seemed ironically to have different motions from the other heavenly bodies and it made more sense for the small earth to move than the immense heavens. But the fact that Copernicus turned the earth into a planet did not cause him to reject Aristotelian physics, for he maintained that “land and water together press upon a single center of gravity; that the earth has no other center of magnitude; that, since earth is heavier, its gaps are filled with water…” ( Revolutions , 10). As Aristotle had asserted, the earth was the center toward which the physical elements gravitate. This was a problem for Copernicus’s model, because if the earth was no longer the center, why should elements gravitate toward it?

The second book of On the Revolutions elaborated the concepts in the first book; book 3 dealt with the precession of the equinoxes and solar theory; book 4 dealt with the moon’s motions; book 5 dealt with the planetary longitude and book 6 with latitude. [ 9 ] Copernicus depended very much on Ptolemy’s observations, and there was little new in his mathematics. He was most successful in his work on planetary longitude, which, as Swerdlow and Neugebauer (77) commented, was “Copernicus’s most admirable, and most demanding, accomplishment…It was above all the decision to derive new elements for the planets that delayed for nearly half a lifetime Copernicus’s continuation of his work – nearly twenty years devoted to observation and then several more to the most tedious kind of computation – and the result was recognized by his contemporaries as the equal of Ptolemy’s accomplishment, which was surely the highest praise for an astronomer.” Surprisingly, given that the elimination of the equant was so important in the Commentariolus , Copernicus did not mention it in book 1, but he sought to replace it with an epicyclet throughout On the Revolutions . Nevertheless, he did write in book 5 when describing the motion of Mercury:

…the ancients allowed the epicycle to move uniformly only around the equant’s center. This procedure was in gross conflict with the true center [of the epicycle’s motion], its relative [distances], and the prior centers of both [other circles]…However, in order that this last planet too may be rescued from the affronts and pretenses of its detractors, and that its uniform motion, no less than that of the other aforementioned planets, may be revealed in relation to the earth’s motion, I shall attribute to it too, [as the circle mounted] on its eccentric, an eccentric instead of the epicycle accepted in antiquity ( Revolutions , 278–79).

Although Copernicus received encouragement to publish his book from his close friend, the bishop of Chelmo Tiedemann Giese (1480–1550), and from the cardinal of Capua Nicholas Schönberg (1472–1537), it was the arrival of Georg Joachim Rheticus in Frombork that solved his needs for a supportive and stimulating colleague in mathematics and astronomy and for access to an appropriate printer. Rheticus was a professor of mathematics at the University of Wittenberg, a major center for the student of mathematics as well as for Lutheran theology. In 1538 Rheticus took a leave of absence to visit several famous scholars in the fields of astronomy and mathematics. It is not known how Rheticus learned about Copernicus’s theory; he may have been convinced to visit Copernicus by one of the earlier scholars he had visited, Johann Schöner, though, as Swerdlow and Neugebauer (16) noted, by “the early 1530’s knowledge of Copernicus’s new theory was circulating in Europe, even reaching the high and learned circles of the Vatican.” Rheticus brought with him some mathematical and astronomical volumes, which both provided Copernicus with some important material and showed him the quality of the mathematical printing available in the German centers of publishing. [ 10 ] Rheticus’s present of the 1533 edition of Regiomontanus’s On all Kinds of Triangles ( De triangulis omnimodis ), for example, convinced Copernicus to revise his section on trigonometry. But Rheticus was particularly interested in showing Copernicus the work of the Nuremberg publisher Johann Petreius as a possible publisher of Copernicus’s volume. Swerdlow and Neugebauer (25) plausibly suggested that “Petreius was offering to publish Copernicus’s work, if not advertising by this notice that he was already committed to do so.” Rheticus wrote the Narratio prima in 1540, an introduction to the theories of Copernicus, which was published and circulated. This further encouraged Copernicus to publish his Revolutions , which he had been working on since he published the Commentariolus .

The Narratio prima was written in 1539 and took the form of a letter to Johann Schöner announcing Copernicus’s findings and describing the contents of the Revolutions . He dealt with such topics as the motions of the fixed stars, the tropical year, the obliquity of the ecliptic, the problems resulting from the motion of the sun, the motions of the earth and the other planets, librations, longitude in the other five planets, and the apparent deviation of the planets from the ecliptic. He asserted that the heliocentric universe should have been adopted because it better accounted for such phenomena as the precession of the equinoxes and the change in the obliquity of the ecliptic; it resulted in a diminution of the eccentricity of the sun; the sun was the center of the deferents of the planets; it allowed the circles in the universe to revolve uniformly and regularly; it satisfied appearances more readily with fewer explanations necessary; it united all the spheres into one system. Rheticus added astrological predictions and number mysticism, which were absent from Copernicus’s work.

The Narratio prima was printed in 1540 in Gdansk (then Danzig); thus, it was the first printed description of the Copernican thesis. Rheticus sent a copy to Achilles Pirmin Gasser of Feldkirch, his hometown in modern-day Austria, and Gasser wrote a foreword that was published with a second edition that was produced in 1541 in Basel. It was published again in 1596 as an appendix to the first edition of Johannes Kepler’s Mysterium cosmographicum (Secret of the Universe), the first completely Copernican work by an adherent since the publications by Copernicus and Rheticus.

The publication of Rheticus’s Narratio prima did not create a big stir against the heliocentric thesis, and so Copernicus decided to publish On the Revolutions . He added a dedication to Pope Paul III (r. 1534–1549), probably for political reasons, in which he expressed his hesitancy about publishing the work and the reasons he finally decided to publish it. He gave credit to Schönberg and Giese for encouraging him to publish and omitted mention of Rheticus, but it would have been insulting to the pope during the tense period of the Reformation to give credit to a Protestant minister. [ 11 ] He dismissed critics who might have claimed that it was against the Bible by giving the example of the fourth-century Christian apologist Lactantius, who had rejected the spherical shape of the earth, and by asserting, “Astronomy is written for astronomers” ( Revolutions , 5). [ 12 ] In other words, theologians should not meddle with it. He pointed to the difficulty of calendar reform because the motions of the heavenly bodies were inadequately known. And he called attention to the fact that “if the motions of the other planets are correlated with the orbiting of the earth, and are computed for the revolution of each planet, not only do their phenomena follow therefrom but also the order and size of all the planets and spheres, and heaven itself is so linked together that in no portion of it can anything be shifted without disrupting the remaining parts and the universe as a whole” ( Revolutions , 5).

Rheticus returned to Wittenberg in 1541 and the following year received another leave of absence, at which time he took the manuscript of the Revolutions to Petreius for publishing in Nuremberg. Rheticus oversaw the printing of most of the text. However, Rheticus was forced to leave Nuremberg later that year because he was appointed professor of mathematics at the University of Leipzig. He left the rest of the management of printing the Revolutions to Andrew Osiander (1498–1552), a Lutheran minister who was also interested in mathematics and astronomy. Though he saw the project through, Osiander appended an anonymous preface to the work. In it he claimed that Copernicus was offering a hypothesis, not a true account of the working of the heavens: “Since he [the astronomer] cannot in any way attain to the true causes, he will adopt whatever suppositions enable the motions to be computed correctly from the principles of geometry for the future as well as for the past …these hypotheses need not be true nor even probable” ( Revolutions, xvi ). This clearly contradicted the body of the work. Both Rheticus and Giese protested, and Rheticus crossed it out in his copy.

Copernicus’s fame and book made its way across Europe over the next fifty years, and a second edition was brought out in 1566. [ 13 ] As Gingerich’s census of the extant copies showed, the book was read and commented on by astronomers (for a fuller discussion of reactions, see Omodeo). Gingerich (2004, 55) noted “the majority of sixteenth-century astronomers thought eliminating the equant was Copernicus’ big achievement.”

While Martin Luther may have made negative comments about Copernicus because the idea of the heliocentric universe seemed to contradict the Bible, [ 14 ] Philip Melanchthon (1497–1560), who presided over the curriculum at the University of Wittenberg, eventually accepted the importance of teaching Copernicus’s ideas, perhaps because Osiander’s preface made the work more palatable. His son-in-law Caspar Peucer (1525–1602) taught astronomy there and began teaching Copernicus’s work. As a result, the University of Wittenberg became a center where Copernicus’s work was studied. But Rheticus was the only Wittenberg scholar who accepted the heliocentric idea. Robert Westman (1975a, 166–67; 2011, chap. 5) suggested that there was a ‘Wittenberg Interpretation’: astronomers appreciated and adopted some of Copernicus’s mathematical models but rejected his cosmology, and some were pleased with his replacement of the equant by epicyclets. One of these was Erasmus Reinhold (1511–1553), a leading astronomer at Wittenberg who became dean and rector. He produced a new set of planetary tables from Copernicus’s work, the Prutenic Tables. Although, as Gingerich (1993, 232) pointed out, “there was relatively little to distinguish between the accuracy of the Alfonsine Tables and the Prutenic Tables ,” the latter were more widely adopted; Gingerich plausibly suggested that the fact that the Prutenic Tables more accurately predicted a conjunction between Jupiter and Saturn in 1563 made the difference. Reinhold did not accept the heliocentric theory, but he admired the elimination of the equant. The Prutenic Tables excited interest in Copernicus’s work.

Tycho Brahe (1546–1601) was the greatest astronomical observer before the invention of the telescope. He called Copernicus a ‘second Ptolemy’ (quoted in Westman 1975, 307) and appreciated both the elimination of the equant and the creation of a planetary system. But Tycho could not adopt the Copernican system, partly for the religious reason that it went against what the Bible seemed to preach. He, therefore, adopted a compromise, the ‘geoheliostatic’ system in which the two inner planets revolved around the sun and that system along with the rest of the planets revolved around the earth.

Among Catholics, Christoph Clavius (1537–1612) was the leading astronomer in the sixteenth century. A Jesuit himself, he incorporated astronomy into the Jesuit curriculum and was the principal scholar behind the creation of the Gregorian calendar. Like the Wittenberg astronomers, Clavius adopted Copernican mathematical models when he felt them superior, but he believed that Ptolemy’s cosmology – both his ordering of the planets and his use of the equant – was correct.

Pope Clement VII (r. 1523–1534) had reacted favorably to a talk about Copernicus’s theories, rewarding the speaker with a rare manuscript. There is no indication of how Pope Paul III, to whom On the Revolutions was dedicated reacted; however, a trusted advisor, Bartolomeo Spina of Pisa (1474–1546) intended to condemn it but fell ill and died before his plan was carried out (see Rosen, 1975). Thus, in 1600 there was no official Catholic position on the Copernican system, and it was certainly not a heresy. When Giordano Bruno (1548–1600) was burned at the stake as a heretic, it had nothing to do with his writings in support of Copernican cosmology, and this is clearly shown in Finocchiaro’s reconstruction of the accusations against Bruno (see also Blumenberg’s part 3, chapter 5, titled “Not a Martyr for Copernicanism: Giordano Bruno”).

Michael Maestlin (1550–1631) of the University of Tübingen was the earliest astronomer after Rheticus to adopt Copernicus’s heliocentricism. Although he wrote a popular textbook that was geocentric, he taught his students that the heliocentric system was superior. He also rejected Osiander’s preface. Maestlin’s pupil Johannes Kepler wrote the first book since the publication of On the Revolutions that was openly heliocentric in its orientation, the Mysterium cosmographicum (Secret of the Universe). And, of course, Kepler eventually built on Copernicus’s work to create a much more accurate description of the solar system.

In 1972 the Polish Academy of Sciences under the direction of J. Dobrzycki published critical editions of the Complete Works of Copernicus in six languages: Latin, English, French, German, Polish, and Russian. The first volume was a facsimile edition. The annotations in the English translations are more comprehensive than the others. The English edition was reissued as follows:

• Minor Works , 1992, trans. E. Rosen, Baltimore: The Johns Hopkins University Press (originally published as volume 3 of Nicholas Copernicus: Complete Works , Warsaw: Polish Scientific Publishers, 1985). Referred to herein as MW .
• On the Revolutions , 1992, trans. E. Rosen, Baltimore: The Johns Hopkins University Press (originally published as volume 2 of Nicholas Copernicus: Complete Works , Warsaw: Polish Scientific Publishers, 1978). Referred to herein as Revolutions .
• On the Revolutions of the Heavenly Spheres , 1955, trans. C.G. Wallis, vol. 16 of Great Books of the Western World , Chicago: Encyclopedia Britannica; 1995, reprint, Amherst: Prometheus Books.
• On the Revolutions of the Heavenly Spheres , 1976, trans. and ed. A.M. Duncan, Newton Abbot: David & Charles.
• “The Derivation and First Draft of Copernicus’s Planetary Theory: A Translation of the Commentariolus with Commentary,” 1973, trans. N.M. Swerdlow, Proceedings of the American Philosophical Society , 117: 423–512.
• Bruno, G., 1977, The Ash Wednesday Supper , trans. E.A. Gosselin and L.S. Lerner, Hamden: Archon Books, 1995; reprint, Toronto: University of Toronto Press.
• Pico della Mirandola, Disputationes adversus astrologiam divinatricem , E. Garin (trans. and ed.), 2 vols., Florence: Vallecchi, 1946, 1952.
• Rheticus, G.J., Narratio prima , in E. Rosen, 1971, 107–96.
• Bardi, A., 2023, “Copernicus and Axiomatics,” in Handbook of the History and Philosophy of Mathematical Practice , B. Sriraman (ed.), Cham: Springer, doi:10.1007/978-3-030-19071-2_110-1
• Blåsjö, V., 2014, “A Critique of the Arguments for Maragha Influence on Copernicus,” Journal for the History of Astronomy , 45: 183–195.
• Blumenberg, H., 1987, The Genesis of the Copernican World , R.M. Wallace (trans.), Cambridge, MA: MIT Press.
• Cohen, I.B., 1960, The Birth of a New Physics , Garden City: Anchor Books; revised edition, New York: W.W. Norton, 1985.
• –––, 1985, Revolutions in Science , Cambridge, MA: Harvard University Press.
• Crowe, M.J., 1990, Theories of the World from Antiquity to the Copernican Revolution , New York: Dover Publications.
• Feldhay, R. and F.J. Ragep (eds.), 2017, Before Copernicus: The Cultures and Contexts of Scientific Learning in the Fifteenth Century , Montreal: McGill-Queens University Press.
• Finocchiaro, M.A., 2002, “Philosophy versus Religion and Science versus Religion: the Trials of Bruno and Galileo,” in H. Gatti (ed.), 51–96.
• Gatti, H. (ed.), 2002, Giordano Bruno: Philosopher of the Renaissance , Aldershot: Ashgate.
• Gillespie, C.C. (ed.), 1970–80, Dictionary of Scientific Biography , New York: Scribner’s.
• Gingerich, O., 1993, The Eye of Heaven: Ptolemy, Copernicus, Kepler , New York: American Institute of Physics.
• –––, 2002, An Annotated Census of Copernicus’ De revolutionibus, Leiden: Brill Academic Publishers; Nuremberg, 1543 and Basel, 1566.
• –––, 2004, The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus , New York: Walker & Company.
• Goldstein, B., 2002, “Copernicus and the Origin of His Heliocentric System,” Journal for the History of Astronomy , 33: 219–235.
• Goddu, A., 2010, Copernicus and the Aristotelian Tradition: Education, Reading, and Philosophy in Copernicus’s Path to Heliocentrism , Leiden: Brill.
• Grendler, P., 2002, The Universities of the Italian Renaissance , Baltimore: The Johns Hopkins University Press.
• Hallyn, F., 1990, The Poetic Structure of the World: Copernicus and Kepler , D. Leslie (trans.), New York: Zone Books.
• Koestler, A., 1989, The Sleepwalkers , London: Penguin, reprint of 1959 edition.
• Koyré, A., 1957, From the Closed World to the Infinite Universe , Baltimore: The Johns Hopkins University Press.
• –––, 1973, The Astronomical Revolution: Copernicus, Kepler, Borelli , R.E.W. Maddison (trans.), Ithaca: Cornell University Press.
• Kuhn, T., 1957, The Copernican Revolution , Cambridge, MA: Harvard University Press.
• Morrison, R., 2014, “A Scholarly Intermediary between the Ottoman Empire and Renaissance Europe,” Isis , 105: 32–57.
• –––, 2017, “Jews as Scientific Intermediaries in the European Renaissance,” in Feldhay and Ragep (eds.), 198–214.
• Omodeo, P.D., 2014, Copernicus in the Cultural Debates of the Renaissance: Reception, Legacy, Transformation , Leiden: Brill.
• Ragep, F.J., 2005, “Ali Qushji and Regiomontanus,” Journal for the History of Astronomy , 36: 359–71.
• –––, 2007, “Copernicus and His Islamic Predecessors,” History of Science , 45: 65–81.
• –––, 2016, “Ibn al-Shatir and Copernicus: The Uppsala Notes Revisited,” Journal for the History of Astronomy , 47: 395–415.
• –––, 2017, “From Tun to Turin: The Twists and Turns of the Tusi Couple,” in Feldhay and Ragep (eds.), 161–97.
• Rosen, E.,1970a, “Copernicus,” in Gillespie (ed.), 3: 401–11.
• –––, 1970b, “Rheticus,” Gillespie (ed.), 11: 395–97.
• –––, 1971, Three Copernican Treatises , 3d ed., New York: Octagon Books.
• –––, 1975, “Was Copernicus’ Revolutions Approved by the Pope?” Journal of the History of Ideas , 36: 531–42.
• –––, 1984, Copernicus and the Scientific Revolution , Malabar, FL: Krieger Publishing Co.
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• Nicolaus Copernicus , in the MacTutor History of Mathematics Archive , maintained by J.J. O’Connor and E.F. Robertson (School of Mathematics and Statistics University of St. Andrews, Scotland).

Aristotle | Bruno, Giordano | Galileo Galilei | Kepler, Johannes | Kuhn, Thomas

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