Copernicus, Nicholas

(b. Torun, Poland, 19 February 1473; d. Frauenburg [Frombork], Poland, 24 May 1543),

astronomy

The founder of modern astronomy lost his father in 1483, when he was only a little more than ten years old. Fortunately his maternal uncle stepped into the breach, so that Copernicus was able to enter the University of Cracow in 1491. His own evaluation of his intellectual indebtedness to that institution was publicly reported as follows at the very time that the end product of his life’s work was in the process of being printed:

The wonderful things he has written in the field of mathematics, as well as the additional things he has undertaken to publish, he first acquired at our university [Cracow] as his source. Not only does he not deny this (in agreement with Pliny’s judgment that to name those from whom we have benefited is an act of courtesy and thoroughly honest modesty), but whatever the benefit, he says that he received it all from our university.¹

Through the influence of his uncle, who had become the bishop of Varmia (Ermland), Copernicus was elected a canon of the cathedral chapter of Frombork (Frauenburg), whose members enjoyed an ample income throughout their lives. In 1496 Copernicus enrolled in the University of Bologna, officially as a student of canon law; but privately he pursued his interest in astronomy, making his earliest recorded observation on 9 March 1497. On 6 November 1500 he observed a lunar eclipse in Rome, where “he lectured on mathematics before a large audience of students and a throng of great men and experts in this branch of knowledge.”²

On 27 July 1501 he attended a meeting of his chapter, which granted him permission to return to Italy for two more years in order to study medicine: “As a helpful physician he would some day advise our most reverend bishop and also the members of the chapter.”³ For his medical studies Copernicus chose Padua, but he obtained a doctoral degree in canon law from the University of Ferrara on 31 May 1503. Returning soon thereafter to Varmia, he spent the remaining forty years of his life in the service of his chapter.

On 31 March 1513 he bought from the chapter’s workshops 800 building stones and a barrel of lime for the purpose of constructing a roofless little tower, in which he deployed three astronomical instruments. He used the parallactic instrument mainly for observing the moon; the quadrant for the sun; and the astrolabe, or armillary sphere, for the stars.

He wrote the first draft of his new astronomical system, De hypothesibus motuum coelestium a se constitutis commentariolus before 1 May 1514 and discreetly circulated a few manuscript copies among trusted friends. The date is that of the catalog of a Cracow professor’s books, which included a “manuscript of six leaves expounding the theory of an author who asserts that the earth moves while the sun stands still,”⁴ This professor was unable to identify the author of this brief geodynamic and heliostatic manuscript because Copernicus, with his customary prudence, had deliberately withheld his name from his Commentariolus. But a clue to the process by which his Commentariolus found its way into the professor’s library is provided by Copernicus’ statement that he reduced all his calculations “to the meridian of Cracow, because… Frombork… where I made most of my observations…is on this meridian [actually, Frombork lies about 1/4° west of Cracow], as I infer from lunar and solar eclipses observed at the same time in both places.”⁵ Furthermore, “as is clear from [lost] letters written with his own hand, Copernicus conferred about eclipses and observations of eclipses with Cracow mathematicians, formerly his fellow students.”⁶

In his Cimmentariolus, Copernicus challenged the astronomical system which had dominated Western thought since the days of Aristotle and Ptolemy. Whereas these two revered authorities and their in numerable followers down through the ages insisted on centering the cosmos around the earth, Copernicus proclaimed that “the center of the earth is not the center of the universe,”⁷ in which position he stationed the sun. Against the geocentrists’ denial of all motion to the earth, the Commentariolus treated “the earth’s immobility as due to an appearance.”⁸ The apparent daily rotation of the heavens results from the real diurnal rotation of the earth. The apparent yearly journey of the sun through the ecliptic is caused by the earth’s real annual revolution about the sun. The apparent alternation of retrograde and direct motion in the planets is produced by the earth’s orbital travel.

“We revolve about the sun like any other planet.”⁹ These portentous words in Copernicus’ Commentariolus assigned to the earth its rightful place in the cosmos. Yet Copernicus laid no claim to priority in this respect (or in any other, since he trod with caution over very dangerous ground). In the compact Commentariolus he briefly recalled that in antiquity the Pythagoreans had asserted the motion of the earth. He later identified two of these Pythagoreans when, in June 1542, he wrote that stirring plea for freedom of thought which serves as the dedication of his Derevolutionibus orbium coelestium (Revolutions of the Heavenly Spheres) Therein he named Philolaus as having believed in the earth’s revolution (not around the sun, but around an imaginary central fire) and Ecphantus as having attributed to the earth an axial rotation (unaccompanied by orbital revolution).

Copernicus carefully refrained from linking Aristarchus with the earth’s motion. He did not hesitate to cite an (unhistorical) determination of the obliquity of the ecliptic by Aristarchus (whom he was misled into confusing with Aristyllus) as 23°51–20”, equal to Ptolemy’s.¹⁰ He also reported an equally unhistorical measurement of the length of the tropical year by Aristarchus (again confused with Aristyllus) as exactly 365_d6_h.¹¹ But the passage in which Copernicus originally associated Aristarchus with Philolaus’s advocay of a moving earth was deleted by Copernicus before he released his De revolutionibus for publication.¹² In like manner, Ptolemy’s discussion of geodynamism conspicuously omitted the name of Aristarchus, who is nevertheless cited in the Syntaxis mathematica in connection with the length of the year.¹³ Copernicus had no desire to inform or remind anybody that the fervently religious head of an influential philosophical school had “thought that the Greeks ought to bring charges of impiety against Aristarchus.”¹⁴ The latter’s superb technical achievements in astronomy were not in question. His geocentric treatise On the Sizes and Distances of the Sun and Moon has survived intact; but his account of the heliocentric system has perished, leaving only a trace of the first such statement in the history of mankind.

According to that pioneering declaration, “the sphere of the fixed stars…is so great that the circle in which Aristarchus assumes the earth to revolve has the same ratio to the distance of the fixed stars as the center of a sphere has to its surface.”¹⁵ Archimedes, who preserved Aristarchus, heliocentric conception by summarizing it in his Sand-Reckoner, objected as a mathematician that “since the center of a sphere has no magnitude, neither can it be thought to have any ratio to the surface of the sphere.”¹⁶ Accordingly, Archimedes interpreted Aristarchus to mean that the ratio earth: distance earth-sun = distance earth-sun; distance earth-stars. Whatever the defects in Aristarchus’ formulation, he unquestionably intended to emphasize the enormous remoteness of the stars.

This fundamental consequence of heliocentrism was expressed in Copernicus’ Commentariolus by the following inequality: distance earth-sun: distance sun-stars < earth’s radius: distance earth-sun. This disproportion is in fact so great that the distance earth-sun is “imperceptible” in comparison with the distance earth-stars or sun-stars.¹⁷ The latter distance measured the size of Copernicus’ universe from the sun at its center to the stars at its outermost limit.

Because he abandoned the geocentrism of his predecessors, he likewise had to enlarge the dimensions of their limited cosmos:

Lines drawn from the earth’s surface and center [to a point in the firmament] must be distinct. Since, however, their length is immense in relation to the earth, they become like parallel lines. These appear to be a single line by reason of the overwhelming distance of their terminus, the space enclosed by them becoming imperceptible in comparison with their length… This reasoning unquestionably makes it quite clear that, as compared with the earth, the heavens are immense and present the aspect of an infinite magnitude, while on the testimony of the senses the earth is related to the heavens as a point to a body, and a finite to an infinite magnitude.¹⁸

On the basis of both reason and sense experience, Copernicus’ heavens “present the aspect of an infinite magnitude.”

But it is not at all certain how far this immensity extends. At the opposite extreme are the smallest, indivisible bodies called “atoms.” Being imperceptible, they do not immediately constitute a visible body when they are taken two or a few at a time. But they can be multiplied to such an extent that in the end there are enough of them to combine in a perceptible magnitude. The same may be said also about the position of the earth. Although it is not in the center of the universe, nevertheless its distance there from is still insignificant, especially in relation to the sphere of the fixed stars.¹⁹

When Copernicus’ atoms are combined in sufficient quantities, they form a visible object. In like manner, when Copernicus’ distance sun-earth is multiplied often enough, the product is Copernicus’ distance sun-stars. Whether that distance was finite or infinite, Copernicus declined to say. Regarding the universe’s “limit as unknown and unknowable,” he preferred to “leave the question whether the universe is finite or infinite to be discussed by the natural philosophers.”²⁰

Had Copernicus elected to extricate himself from this perennial cosmological dilemma by voting for infinity, he would have had to surrender the sun’s centrality, since of course the infinite can have no center. On the other hand, had he retained the limited dimensions of the traditional cosmos, the yearly orbit of his moving earth should have produced an annual parallax of the stars. This perspective displacement is in fact so minute that mankind had to wait nearly three centuries for telescopes sensitive enough to detect it. Copernicus’ solution, therefore, was to impale himself on neither horn of the dilemma by declaring the universe to be “similar to the infinite.”²¹ The qualification “similar” permitted him to regard the universe as capable of possessing a center, while the similarity to the infinite explained the naked eye’s inability to perceive annual stellar parallax.

It Copernicus hoped to gain acceptance for his revival of the concept of a moving earth, he had to overcome the ancient objections to such motion. Earth was traditionally regarded as one of the four terrestrial or sublunar elements, the other three being water, air, and fire, whereas the heavenly bodies consisted of a fifth element. Aristotle’s theory of the motion of these five elements was summarized by Copernicus are follows:

The motion of a single simple body is simple; of the simple motions, one is straight and the other is circular; of the straight motions, one is upward and the other is downward. Hence every simple motion is either toward the middle, that is, downward; or away from the middle, that is, upward; or around the middle, that is, circular. To be carried downward, that is, to seek the middle, is a property only of earth and water, which are considered heavy; on the other hand, air and fire, which are endowed with lightness, move upward and away from the middle. To these four elements it seems reasonable to assign rectilinear motion, but to the heavenly bodies, circular motion around the middle.²²

Copernicus has transferred the earth to the category of the heavenly bodies, to which circular motion around the middle could be reasonably assigned. Yet some part of the earth undeniably “sink of their own weight,” while “if any part of the earth is set afire, it is carried from the middle upwards,”²³ Such

rectilinear motion, however, overtakes things which leave their natural place or are thrust out of it or quit it in any manner whatsoever… Whatever falls moves slowly at first, but increases its speed as it drops. On the other hand, we see this earthly fire… after it has been lifted up high, slacken all at once… Circular motion, however, always rolls along uniformly, since it has an unfailing cause. But rectilinear motion has a cause that quickly stops functioning. When rectilinear motion brings to their own place,… their motion ends.²⁴

Retaining Aristotle’s doctrine that every body has its natural place in the universe, Copernicus confined the application of this principle to the displaced parts of the earth, which were subject to the sort of motion classified by Aristotle as violent. Copernicus’ planet earth as a whole, on the other hand, possessed perpetual motion, natural to the heavenly bodies. This circular motion was shared by any portion of the earth temporarily detached from it: “The motion of falling and rising bodies in the framework of the universe is twofold, being in every case a compound of straight and circular… Hence, since circular motion belongs to wholes, but parts have rectilinear motion in addition, we can say that circular subsists with rectilinear as animal does with sick,:²⁵ Taken as a whole, earth has only circular motion and no rectilinear motion, just as a healthy animal has no sickness. But a loose portion of the earth has rectilinear motion conjoined with circular motion, just as a diseased beast unites sickness with its animal nature.

The three conventional classes of motion, therefore, do not correspond to entirely separate physical states. “Aristotle’s division of simple motion into three types, away from the middle, toward the middle, and around the middle, will be construed as merely an exercise in logic.”²⁶ Similarly, in geometry “we distinguish the point, the line, and the surface, even though one cannot exist without another, and none of them without body.”²⁷

Besides reinterpreting the traditional theory of motion to fit the requirements of his moving earth, Copernicus endowed the planet earth, as opposed to its disjointed parts, with natural, not violent, motion. Ptolemy had contended that the earth’s axial rotation.

would have to be exceedingly violent and its speed unsurpassable to carry the entire circumference of the earth around in twenty-four hours. But things which undergo an abrupt rotation seem utterly unsuited to gather bodies to themselves, and seem more likely, if they have been produced by combination, to fly apart unless they are held together by some bond. The earth would long ago..have burst asunder…and dropped out of the skies.²⁸

Ptolemy’s anxiety was answered by Copernicus:

what is in accordance with nature produces effects contrary to those resulting from violence. For, things to which force or violence is applied must disintegrate and cannot long endure, whereas that which is brought into existence by nature is well ordered and preserved in its best state. Therefore Ptolemy has no cause to fear that the earth and everything earthly will be disrupted by a rotation created through nature’s handiwork, which is quite different from what art or human intelligence can contrive.²⁹

Ptolemy was further concerned that “living creatures and any other loose objects would by no means remain unshaken… Moreover, clouds and anything else floating in the air would be seen drifting always westward,” since the earth’s axial rotation whirls it round swiftly eastward.³⁰ In reply Copernicus asked:

With regard to the daily rotation, why should we not admit that the appearance is in the heavens and the reality in the earth?… Not merely the earth and the watery element joined with it have this motion, but also no small part of the air…[The reason may be] either that the nearby air, mingling with earthy or watery matter, conforms to the same nature as the earth, or that [this] air’s motion, acquired from the earth by proximity, shares without resistance in its unceasing rotation.³¹

By contrast with the upper layers of air, the lower layers are firmly attached to the earth and rotate with it. This partnership answers the argument that “objects falling in a straight line would not descend perpendicularly to their appointed place, which would meantime have been withdrawn by so rapid a movement” as the earth’s rotation.³² Pro-Copernicans and anti-Copernicans later conducted experiments to determine whether an object dropped vertically from a height, stationary or moving with respect to the earth’s surface, fell precisely at the foot of the height. The divergent results of these numerous trials were variously interpreted; and decisive experimental confirmation of the earth’s daily rotation was first provided by Foucault’s pendulum in 1851, not long after Bessel, F. G. W. Struve, and T. Henderson published their independent discoveries of annual stellar parallax as direct observational proof of the earth’s yearly orbital motion.

In addition to the diurnal rotation and annual revolution, Copernicus felt obliged to ascribe to the earth what he called its “motion in declination.”³³ When prolonged, the axis about which our planet rotates daily meets the firmament at the celestial poles. Midway between these poles lies the celestial equator, the intersection of the plane of the earth’s equator and the celestial sphere. In performing its annual revolution around the sun, the earth describes what Copernicus termed, “grand circle” the plane of which cuts the celestial sphere in the ecliptic. The poles of the ecliptic are the end points of the axis of the earth’s orbital revolution. The plane of that revolution, or ecliptic, is inclined to the celestial equator at an angle known as the obliquity of the ecliptic. As Copernicus said in the Commentariolus “The axis of the daily rotation is not parallel to the axis of the grand circle, but is inclined to it at an angle that intercepts a portion of a circumference, in our time about 23 1/2°”³⁴

In Copernicus’ time a spherical body revolving in an orbit was considered to be attached inflexibly to the orbit’s center, as though from this hub a rigid spoke ran right through the revolving ball. Therefore, if the earth were subject only to the diurnal rotation and annual revolution without the third motion in declination

no in equality of days and nights would be observed. On the contrary, it would always be either the longest or shortest day or the day of equal daylight and darkness, or summer or winter, or whatever the character of the season, it would remain identical and unchanged. Therefore the third motion in declination is required….[The motion in declination] is also an annual revolution but… it occurs in the direction opposite to that of the [orbital] motion of the [earth’s] center. Since these two motions are opposite in direction and nearly equal [in period], the result is that the earth’s axis and… equator face almost the same portion of the heavens, just as if they remained motionless. ³⁵

The function of Copernicus’ third motion in declination was to keep the earth presenting a virtually unchanging aspect to an observer viewing it from a distant star, whereas to a spectator stationed on the sun it would constantly pass through its cyclical seasonal changes. Without the motion in declination Copernicus’ earth would always look the same as seen from the sun, while its axis of rotation would describe a huge conical surface in space instead of pointing toward the vicinity of the same star.

The rotational axis, however, is not directed toward precisely the same star because

the annual revolutions of the center and of declination are nearly equal. For if they were exactly equal, the equinoctial and solstitial points as well as the entire obliquity of the ecliptic would have to show no shift at all with reference to the sphere of the fixed stars. But there is a slight variation, which was discovered only as it grew larger with the passage of time³⁶

This slight variation, the precession of the equinoxes, had been explained by Ptolemy as due to a slow eastward rotation of the sphere of the stars. But that sphere had to remain absolutely motionless in the cosmos of Copernicus, who had replaced the apparent daily rotation of the stars by the real axial rotation of the earth.

In like manner, for Ptolemy’s motion of the starry sphere in 36,000 years, Copernicus substituted the behavior of the earth

[Its] two revolutions, I mean, the annual declination and [the orbital motion of] the earth’s center, are not exactly equal, the declination being of course completed a little ahead of the period of the center. Hence, as must follow, the equinoxes and solstices seem to move forward. The reason is not that the sphere of the fixed stars moves eastward, but rather that the equator moves westward³⁷

Whereas modern astronomy has adopted Coperinicus’ account of precession, its rate eluded him. The modern constant value, about 50” a year, was regarded by him as the mean rate of precession: he was misled by his predecessors’ divergent determinations of this minute quantity into believing that it under went a cyclical variation. He likewise made the same error regarding the obliquity of the ecliptic. The available evidence warranted only the conclusion that the obliquity diminished progressively. Nevertheless, he supposed that after decreasing from a maximum of 23°52’before Ptolemy’s time to a minimum of 23°28’ after his own time, it would then reverse itself and in crease to its previous maximum, oscillating thereafter in a 24‘ cycle of long period.

The sun appears to move with annually recurring variations of speed along its course in the ecliptic, thereby making the four seasons unequal in length. To represent these phenomena, Ptolemy had the sun traverse a circle whose stationary center was separated by some distance from the earth. This eccentric circle’s apogee, or point at which the sun attained its greatest distance from the earth, was regarded by Ptolemy as fixed in relation to the stars at 24°30’ before the summer solstice. Al-Bāttanī located the apogee only 7° 43’ before the summer solstice.³⁸” In the 740 years since Ptolemy it advanced nearly 17³⁹ Al-Zarqālī, however, “Put the apogee 12°10’ before the solstice.⁴⁰ Thus

in 200 years it retrogessed 4° or 5°. Thereafter until our age it moved forward. The entire period [from Ptolemy to Copernicus] has witnessed no other retrogression nor the several stationery points which must intervene at both limits when motions reverse their direction. [The absence of] these features cannot possibly be understood in a regular and cyclical motion. Therefore many astronomers believe that some error occurred in the observations of those men [al-Battani and al-Zarqālī]. Both were equally skillful and careful astronomers so that it is doubtful which one should be followed. For my part I confess that nowhere is there a greater difficulty than in understanding the solar apogee, where we draw large conclusions from certain minute and barely perceptible quantities… As can be noticed in the general structure of the [apogee’s] motion, it is quite probably direct but nouniform. For after that stationary interval from Hipparchus to Ptolemy the apogee appeared in a continuous, regular, and accelerated progression until the present time. An exception occurred between al-Battānī and al-Zarqālī through a mistake (it is believed), since everything else seems to fit ⁴¹

Copernicus still believed in the fixity of the earth’s aphelion, or—its Ptolemaic counterpart—the solar apogee, when he composed the Commentariolus between 15 July 1502 and 1 May 1514. Later, in writing book III of De revolutionoibus, where he took into account the related work of the Arab astronomers, he made the terrestrial aphelion move. But, the observations of al-Battā;nī and al-Zarqālī being discordant, he was “doubtful which one should be followed.” By the summer of 1539, when his disciple Rheticus drafted the Narratio prima (First Report) of the Copernican system to be presented in printed form to the reading public., both al-Battānī and al-Zarqālī were suspect in Copernicus’ mind. In creating his model for the progressive motion of the earth’s aphelion, Copernicus felt justified in lowering al-Battānī’s determination by 6° and raising al-Zarqālī’s by 4°

Now you see [says Rheticfus] what great effort my teacher had to put forth to determine the mean motion of the [solar] apogee. For nearly forty years in Italy and here in Frombork, he observed eclipse and the [apparent] motion of the sun. He selected the observation by which he established that in a.d. 1515 the solar apogee was at 6 2/3° of Cancer [= 6 2/3° after the solstice]. Then examining all the eclipse in Ptolemy and comparing them with his own very careful observations, he concluded that the mean annual motion of the apogee with reference to the fixed stars was about 25”…..⁴²

In his earliest recorded observation, made in Bologna after sunset on 9 March 1497, Copernicus reported an occultation of Aldebaran by the moon. In his De revolutionibus he used this observations to support his computation of the lunar parallax.⁴³ The variation in this quantity and in the length of the moon’s apparent diameter was greatly exaggerated in Ptolemy’s lunar theory, as Copernicus emphasized in the Commentariolus

The consequence by mathematical analysis is that when the moon is in quadrature, and at the same time in the lowest part of the epicycle, it should appear nearly four times greater (if the entire disk were luminous) than when new and full, unless its magnitude increases and diminishes is no reasonable way. So, too because the size of the earth is sensible in comparison with its distance from the moon, lunar parallax should increase very greatly at the quadratures. But if anyone investigates these maters carefully, he will find that in both respects the quadratures differ very little from new and full moon..⁴⁴

Mounting the moon on an epicycle whose deferent was not concentric with the earth, Ptolemy and his followers had the epicycle’s center traverse equal arcs in equal times as measured from the earth’s center. While Copernicus’ predecessors “declare that the motion of the epicycle’s center is uniform around the center of the earth, they must also admit that it is nonuniform on its own eccentric, which it describes”⁴⁵ Such a model was rejected by the Commentariolus as conflicting with “the rule of absolute motion,” according to which “everything would move uniformly about its proper center.”⁴⁶ This principle was violated a second time in the Ptolemaic lunar theory, which had the moon traverse equal arcs on its epicycle, as measured not from the epicycle’s center but from a different point known as the equant or the equalizing point.

In order to avoid using an equant, which he regarded as an impressible device, in his own lunar theory Copernicus obtained an equivalent result by piling on the traditional epicycle a second, smaller epicyclet carrying the moon. This method of adhering to the axiom of uniform motion, at the same time eliminating the equant and the excessive variation in the length of the moon’s apparent diameter, had been adopted in the Muslim world by Ibn al-Shāṭir about a century before Copernicus was born. Was Copernicus aware of the work done by his Damascene predecessor? The latter introduced a second epicycle for the sun too, but Copernicus did not follow suit. He used eccentric models, which had been rejected by Ibn al-Shātir. His numerical results also differed being based in part on his own observations. Since he knew no Arabic and Ibn al-Shāṭir’s manuscript had not been translated into any own observations. Since he knew no Arabic and Ibn al-Shaṭir’s manuscript had not been translated into any language understood by Copernicus, presumably he had no direct acquaintance with the Muslim’s thinking. Their conclusions, independently reached, strikingly converged on the same theoretical and practical shortcomings in Ptolemaic astronomy. But there is no inkling of geodynamism in Ibn al-Shāṭir.

The same cannot be said about Ibn al-Shāṭir’s contemporary, Nicole Oresme, who around 1377 made the first translation of Aristotle’s De caelo into a modern language. In his commentary Oresme considered many arguments concerning the diurnal rotation, which should more reasonably, it seemed to him, be assigned to the earth. Yet he admitted that he had discussed this idea “for fun”⁴⁷ and, as bishop of Lisieux, he rejected it on the basis of Biblical passages. Oresme’s translation-commentary was written in French (which Copernicus did not understand) and was first printed in 1941–1943. Had Copernicus been familiar with it, he would have noticed its complete silence about the earth’s orbital revolution. He would surely have been impressed by Oreme’s reasoning that the earth benefits from the sun’s heat, and in familiar contexts, that what “is roasted at a fire receives the heat of the fire around itself because it is turned and not because the fire is turned around it.”⁴⁸ That Copernicus had any direct acquaintance with Oresme seems out of the question.

Nevertheless, university teaching may well have been affected by Oresme and even more by his older friend, Jean Buridan. The latter’s discussion in Latin of Aristotle’s De caelo mentioned the idea that “the earth, water, and air in its lower region move jointly with daily rotation.”⁴⁹ Buridan also set forth the following argument:

An arrow shot vertically upward from a bow falls back on the same place on the earth from which it was discharged. This would not happen it the earth moved so fast. In fact, before the arrow fell, the part of the earth from which it was fired would be a mile away.⁵⁰

The absence of the earth’s orbital revolution from the thinking of Copernicus’ Muslim and Christian predecessors, as well as his use of Arabic observational results, indicate that he did not conceal any intellectual indebtedness to them. On the other hand, with complete openness he expressly acknowledged being inspired by his ancient geodynamic forerunners. Their ideas, however, came down to him as the barest of bones; it was he who first fleshed out the geodynamic astronomy.

Copernicus did away with the stationary earth situated at the center of the Aristotelian-Ptolemaic universe. In his cosmos the earth revolved around the central sun in an annual orbit and at the same time executed its daily rotations. Consequently, the astronomer who inhabits the earth watches the stately celestial ballet from an observatory that is itself both spinning and advancing.

It any motion is ascribed to the earth, in all things outside it is same motion will appear, but in the opposite direction, as though they were moving past it. This is the nature in particular of the daily rotation, since it seems to involve the entire universe, except the earth and what is around it. However, if you grant that the heavens have no part in this motion but that the earth rotates from west to east, upon earnest consideration you will find that this is the actual situation, as far as concerns the apparent rising and setting of the sun, moon, stars, and planets.⁵¹

Three of the planets in Copernicus’ cosmos revolve around the sun in orbits larger in size and longer in period than the earth’s. Each of these three outer, or superior, planets (Mars, Jupiter, and Saturn in ascending order)

seems from time to time to retrograde, and often to become stationary. This happens by reason of the motion, not of the planet, but of the earth changing its position in the grand circle. For since the earth moves more rapidly than the planet, the line of sight directed [from the earth] toward [the planet and] and firmament regresses, and the earth more than neutralizes the motion of the planet. This regression is most notable when the earth is nearest to the planet, that is, when it comes between the sun and the planet at the evening rising of the planet. On the other hand, when the planet is setting in the evening or rising in the morning, the earth makes the observed motion greater than the actual. But when the line of sight is moving in the direction opposite to that of the planets and at an equal rate, the planets appear to be stationary, since the opposed motions neutralize each other.⁵²

As an outer planet in its normal eastward progression (viewed against the background of the more distant stars) slows down, stops, reverses its direction, stops again and resumes its direct march, it appears to pass through kinks or loops. These were actual celestial happenings for Ptolemy and his followers. The true nature of these planetary loops was revealed for the first time by Copernicus when he analyzed them in detail as side effects of the observation of the slower planet from the faster earth. The loops are optical illusions, not real itineraries.

Two entirely different motions in longitude appear in them (the planets. One is caused by the earth’s motion… and the other is each [planet’s] own proper motion. I have decided without any impropriety to call the first one a parallactic motion, since it is this which makes the stations, direct motions, and retrogressions appear in all of them. These phenomena appear, not because the planet, which always moves forward with its own motion, is erratic in this way, but because a sort of parallax is produced by the earth’s motion according as it differs in size from those orbits.⁵³

Before Copernicus there was much uncertainty regarding the position of Venus and Mercury in the heavens. But the Copernican system located these two bodies correctly as the inferior, or, lower, planets, revolving around the central sun inside the earth’s orbit and at a greater speed.

The true places of Saturn, Jupiter, and Mars become visible to us only at their evening rising, which occurs about the middle of their retrogradations. For at that time they coincide with the straight line through the mean place of the sun [and earth], and are unaffected by that parallax. For Venus and Mercury, however, a different relation prevails. For when they are in conjunction with the sun, they are completely blotted, out and are visible only while executing their elongations to either side of the sun, so that they are never found without this parallax.

Consequently each planet has its own individual parallactic revolution. I mean, terrestrial motion in relation to the planet, which these two bodies perform mutually. Combined in this way, the motions of both bodies display themselves interconnected… The motion in parallax, I submit, is nothing but the difference by which the earth’s uniform motion exceeds the planet’s motion, as in the cases of Saturn, Jupiter, and Mars, or is exceeded by it, as in the cases of Venus and Mercury.⁵⁴

The motion in parallax is smaller, as regards the inner planets, for Venus than for Mercury, and as regards the outer planets, smaller for Mars than Jupiter and Saturn. Hence.

the forward and backward arcs appear greater in Jupiter than in Saturn and smaller than in Mars, and on the other hand, greater in Venus than in Mercury. This reversal of direction appears more frequently in Saturn than in Jupiter, and also more rarely in Mars and Venus than in Mercury.⁵⁵

Although the sun was nominally one of the seven Ptolemaic planets, it actually possessed of privileged status in that system. Thus, the center of the epicycle on which Venus was mounted kept exact pace with the sun. This synchronization was accomplished by having the line drawn from the central stationary earth to the annually revolving sun always pass through the center of Venus’s epicycle. As a result, Venus’s maximum distance to either side of the sun was regulated by the length of the radius of its epicycle. In Ptolemy’s words, “the greatest elongations of Venus and Mercury [occur] when the planet reaches the point of contact of the straight line drawn from our eye tangent to the epicycle,”⁵⁶ This statement applied to Mercury, even though its more irregular motion required a somewhat more complicated arrangement.

In the Ptolemaic theory of the three outer planets the sun again played a special part. As the planet revolved on its epicycle, the radius drawn from the center of the epicycle to the moving planet kept step with the sun revolving around the stationary earth. This coordination was achieved by having the planet’s radius vector parallel at all times to the line drawn from the terrestrial observer to the (mean) sun.

Thus, the Ptolemaic theory of each of the three outer and two inner planets introduced the annual revolution. This was imputed by the Ptolemaists to the sun, which they regarded as one of the planets. But they did not explain why the orbital motion of one planet should be so especially privileged as to be an integral part of the theory of five other planets.

In still another respect the sun occupied a privileged position in Ptolemaic astronomy; The sun was placed “between those [planets] which pass through every elongation from it and those which do not so behave, but always move in its vicinity.”⁵⁷ Copernicus protested that this argument “carried no conviction because its falsity is revealed by the fact that the moon too shows every elongation from the sun.”⁵⁸ Whatever their other disagreements, Ptolemaists and Copernicans alike separated the moon from the outer planets.

The removal of the sun from the category of the plants was one of Copernicus’ most influential contributions to the advancement of astronomy. The limited maximum elongations of Venus and Mercury no longer resulted from the lengths of the radii of their epicycles but were caused by a physical fact; since they were now the inner planets, their orbits lay entirely within the earth’s. Therefore, these planets could never be seen from the earth at an angular distance from the sun exceeding 48° for Venus and 28° for Mercury. Hence, these planets could never come to quadrature or opposition, where the difference in geocentric longitude between them and the sun would have to reach 90° or 180°.

In the case of each of the three outer planets, the perpetually parallel orientations of the epicycle’s radius directed to the planet and of the line earth-sun were no longer an unexplained coincidence but rather an indication of a physical phenomenon, the earth’s orbital revolution around the sun. This “one motion of the earth causes all these phenomena, which the ancient astronomers sought to obtain by means of an epicycle for each” of the three outer planets.⁵⁹ By making the earth a planet (or planetizing it, so to say) and deplanetizing the sun, Copernicus took a long step away from previous misconceptions toward the correct understanding of our physical universe;

Venus seems at times to retrograde, particularly when it is nearest to the earth, like the superior planets, but for the opposite reason. For the regression of the superior planets happens because the motion of the earth is more rapid than theirs, but with Venus, because it is slower; and because the superior planets enclose the grand circle [earth’s orbit], whereas Venus is enclosed within, it. Hence Venus is never in opposition to the sun, since the earth cannot come between them, but it moves within fixed distances on either side of the sun. These distances are determined by tangents to the circumference drawn from the center of the earth, and never exceed 48° in our observations.⁶⁰

From the maximum elongation of Venus, Copernicus was able to obtain the first approximately correct planetary distances, which he expressed in terms of the distance earth-sun. This distance, which subsequently become the fundamental astronomical unit, was grossly underestimated by Copernicus, who simply followed the ancient error in this respect. But in computing the distances of the other five planets from the sun as ratios of the distance earth-sun, Copernicus came remarkably close to the values accepted today. For Mars and Venus, he agreed to the second decimal place (1.52, 0.72), and for Jupiter to the first (5.2) For Saturn and Mercury, however, he was less accurate (9.2 as compared with 9.5; 0.376 as compared with 0.387).

In this respect the contract with the geocentric astronomy is instructive. Ptolemy was familiar with two proposed locations for Venus and Mercury; either below the sun or above it. No transits of the sun by either Venus or Mercury had ever been observed. But the absence of such reports could be explained if the inferior planet’s did not coincide with the sun’s. “Nor can such a determination be reached in any other way, because none of the planets undergoes a perceptible parallax, the only phenomenon from which the [planetary] distances are obtained.”⁶¹ Differences in parallax were regarded by Ptolemy as the only method for arranging the planets in the ascending order of distance from the earth. Such parallaxes being unavailble to him, in the Syntaxis, he virtually renounced the effort to ascertain the distances of the planets. But Copernicus, by using the astronomical unit as his measuring rod, succeeded in establishing the correct order and distance of the known planets with a high degree of accuracy.

Although he did not accept the widespread belief that every planet was moved by a resident angel or spirit, he prudently refrained from explicitly rejecting that popular doctrine. He held instead that, just as physical bodies become spherical when they are unified, so

the motion appropriate to a sphere is rotation in a circle. By this very act the sphere express its from as the simplest body, wherein neither beginning nor end can be found, nor can the one be distinguished from the other, while the sphere, itself traverses the same points to return upon itself.⁶²

Had Copernicus possessed the courage or insight to push this principle to its logical outcome, he would not have left the axial rotation of the sun and planets to be discovered by his followers.

The Copernican celestial spheres, which expressed their from by rotating in a circle, were mainly those which carried either the planets or the planet-carrying spheres. In the former case, the planet was attached to the surface of the sphere at its equator, like a pearl on a ring; however, whereas the pearl was visible, the ring was not. Equally invisible was the rest of the planet-carrying sphere, that is, the sphere, of the epicycle. The whole of the deferent sphere, which carried the sphere of the epicycle, was likewise imperceptible. Although Copernicus never explicitly asserted the physical existence of these unseen spheres, he never denied their reality and always implicitly assumed it. Thus, orbium in the title of his De revolutionibus orbium colestium referred not to the planetary bodies themselves but to the spheres which carried them or helped to do so. In banishing these spheres from astronomy, Tycho Brahe said,

There really are not any sphere in the heavens.. Those which have been devised by the experts to save the appearances exist only in the imagination, for the purpose of enabling the mind to conceive the motion which the heavenly bodies trace in their course and, by the aid of geometry, to determine the motion numerically through the use of arithmetic.⁶³

Although Copernicus always proceed on the assumption that the planetary motions were produced by spheres of one sort, or another, he was not unswervingly committed to any particular kind of sphere. Thus, in expounding the motion of the solar apogee, he resorted to an eccentreccentric—that is, an eccentric sphere or circle whose center was carried around by the circumference of a second, smaller eccentric sphere, pr circle. Then he explained that equivalent results would follow from an epicyclepicyclet-that is, an epicyclet whose center was carried round by an epicycle, whose center in turn revolved on the circumference of a deferent concentric with the sun as the center of the universe. Moreover, mounting an epicycle on an eccentric would serve the purpose as well; “Since so many arrangements lead to the same numercial outcome, I could not reality say which exists, except that on account of the unceasing agreement of the computations and the phenomena I must believe it to be one of them.⁶⁴

In his youthful Commentariolus Copernicus located each of the three outer planets on an epicyclet, whose center rode on a larger epicycle carried by a concentric deferent. This device had been called “concentrobiepicyclic” in contradistinction to the eccountrepicyclic arrangement preferred by Copernicus in his mature Derevolutionibus. His later shift to the single epicycle mounted on an eccentric deferent was not arbitrary; it was connected with his conclusion that the sun’s displacement from the center of the universe was variable and not constant, as he had originally believed on the strength of Ptolemy’s statement to that effect.

The center of Copernicus’ universe was not the body of the sun, but a nearby unoccupied point. This purely mathematical entity could not fulfill the function served by the center of the pre-Copernican universe. In that cosmos, according to Aristotle, its principal architect, “the earth and the universe happen to have the same center. A heavy body moves also toward the center of the earth, but it does so only incidentally, because the earth has its center at the center of the universe.”⁶⁵ Having planetized the earth and raised it out of the universe’s center to the third circumsolar orbit, Copernicus could not regard his new planet as the collection depot for all the heavy bodies on the move in the universe. On the other hand, he had no reason to deny that heavy terrestrial objects tended toward the earth’s center. Hence, he put forward a revised conception of gravity, according to which heavy objects everywhere tended toward their own center—heavy terrestrial objects toward the center of the earth, heavy lunar objects toward the center of the moon, and so on;

For my part, I think that gravity is nothing but a certain natural striving with which parts have been endowed… so that by assembling in the form of a sphere they may join together in their unity and wholeness. This tendency may be believed to be present also in the sun, the moon, and the other bright planets, so that it makes them keep that roundnesss which they display,⁶⁶

Whereas the pre-Copernican cosmos had known only a single center of gravity or heaviness, the physical universe acquired multiple centers of gravity from Copernicus who thus opened the road that led to universal gravitation.

This contribution to one of the basic concepts of modern physics and cosmology confirms what we have already witnessed in many other aspects of Copernicus’ thought. He was firmly convinced that he was talking about the actual physical world when he transformed the earth from the sluggish dregs of the universe to a satellite spinning about its axis as it whirled around the sun. He would have spurned the doctrine (had he been familiar with it) propounded by Buridan, who said, “For astronomers, it is enough to assume a way of saving the phenomena, whether it is really so or not,⁶⁷

By a quirk of fate, control over the printing of the first edition of Copernicus’ De revolutionibus passed into the hands of an editor who shared Buridan’s fictionalist conception of scientific method in astronomy. Taking advantage of the dying author’s remoteness from the printing shop and at the same time concealing his own identity, Andres Osiander inserted in the most prominent place available, the verso of the title page, an unsigned address “To the Reader, Concerning the Hypotheses of This Work.” Therein the reader was not informed that Copernicus used the word “hypothesis” in its strictly etymological sense as equivalent to “fundamental categorical proposition”, not in the derivative meaning of “tentative conjecture.” Nor was the reader told that in private correspondence with the editor, Copernicus had steadfastly repudiated the principal tenet in the interpolated address: The astronomer’s “hypotheses need not be true nor even probable; if they provide a calculus consistent with the observations, that alone is sufficient.”⁶⁸ Thus it came to pass that Copernicus’ De revolutionibus, now universally recognized as a classic of science, was first presented to the civilized world in a guise which, however, well intentioned, falsified its essential nature and fooled many readers, including J. B. J. Delambre, the renowned nineteenth-century historian of astronomy.

NOTES

1. Albert Caprinus, Indicium astrologicm (Cracow, 1542), dedication (cited in Prowe, 1, 1,148).

2. Rosen, p.111

3. Prowe, 1, 1, 291

4. Rosen, p.67

5.De revolutionibus, IV, 7; cf, III, 18, 19

6. Simon Starwolski’s biography of Copernicus (cited in Prowe 1, 1, 149)

7. Rosen, p.58

8.Ibid., p.59

9.Ibid.

10.Derevolutionibus, III, 2

11.Ibid.,13

12.Gesamtausgabe, II 30

13. III, 1;Heiberg, ed. 1, 203: 10, 206–5-6,25

14. Plutarch, Face in the Moon, 923A.

15. Thomos L. Heath, Aristarchus of Samos (Oxford, 1959) p, 302 (trans, modified)

16. Heath, The Works of Archimedes (Cambridge, 1897; Doved ed.., New York., n.d) p.22 (trans modified)

17. Rosen. p.58

18.De revolutionibus, 1,6

19.Ibid.

20.Ibid.,8.

21.Gesmatausgab, II 31

22.De revolutionibus, 1,7

23.Ibid.,8

24.Ibid.

25.Ibid.

26.Ibid

27.Ibid

28.Ibid, 7

29.Ibid., 8.

30.Ibid., 7.

31.Ibid., 8.

32.Ibid., 7.

33. Rosen, p. 63

34.Ibid., pp. 63–64.

35. De revolutionibus, 1. 11.

36.Ibid.,

37.Ibid., III, 1.

38.Ibid., 16.

39.Ibid., 20.

40.Ibid., 16.

41.Ibid., 20.

42. Rosen, p. 125.

43.De revolutionibus, IV, 27.

44. Rosen, p. 72.

45.De revolutionibus, IV, 2.

46. Rosen, pp. 57–58.

47. Nicole Oresme, “Le livre du ciel et du monde,” ed. and with commentary by Albert D. Menut and Alexander J. Denomy, in Mediaeval Studies, 4 (1942), 279 (§144c).

48.Ibid., p. 277 (§142b).

49.Questiones super libris quattuor De caelo et mundo, E. A. Moody, ed. (Cambridge, Mass., 1942), p. 229.

50.Ibid.

51.De revolutionibus, 1, 5.

52. Rosen, pp. 77–78.

53.De revolutionibus, V, 1.

54.Ibid.

55.Ibid., 1, 10.

56. Ptolemy, Syntaxis mathematica, X, 6; Heiberg, ed., II, 317:13–17.

57.Ibid., V, 3.

58.De revolutionibus, 1, 10.

59.Ibid., V, 3.

60. Rosen, p. 83.

61. Ptolemy, IX, 1; Heiberg, ed., II, 207:13–16.

62.De revolutionibus, 1, 4.

63. Tycho Brahe, Opera omnia, J. L. E. Drayar, ed., 15 vols. (copenhagem 1913–1929), IV,222:24–28.

64.De revolutionibus, III, 20.

65. Aristotle, De caelo, II, 14; 296b 15–18.

66.De revolutionibus, 1, 9.

67. Buridan, p. 229.

68. Rosen, p. 25.

BIBLIOGRAPHY

A 2nd ed. of Henryk Baranowski’s Bibliografia Kopernikowska 1509–1955 (Warsaw, 1958) is being prepared in connection with the celebration in 1973 of the 500th anniversary of the birth of Copernicus. An annotated Copernicus bibliography for 1939–1958 is included in Three Copernican Treatises, trans., ed., and with an introduction by Edward Rosen, 2nd ed. (New York, 1959), which also contains an English translation of Copernicus’ Commentariolus and Letter Against Werner and Rheticus’ Narratio prima. An English translation of Copernicus’ De revolutionibus orbium coelestium is in Great Books of the Western world vol. XVI (Chicago, 1952). The Latin text of De revolutionibus and a photocopy of Copernicus’ autograph manuscript are available in Nikolaus Kopernikus Gesamtausgabe, 2 vols. (Berlin-Munich, 1944–1949). The standard biography by Leopold Prowe, Nicolaus Coppernicus, 2 vols. (Berlin, 1883–1884; repr., Osnabrück, Germany, 1967), has not yet been superseded, even though it is incomplete (the planned third volume was never published), nationalistically biased, scientifically inadequate, somewhat inaccurate, and partly obsolete.

Edward Rosen

COPERNICUS, NICHOLAS

(b. Toru, Poland, 19 February 1473;

d. Frauenburg [Frombork], Poland, 24 May 1543), astronomy, cosmology. For the original article on Copernicus see DSB, vol. 3

Scientists value accuracy, precision, consistency, coherence, and other like characteristics. There was not a great deal that Nicholas Copernicus contributed or, arguably, could have contributed to the greater factual accuracy and precision of astronomy. But inconsistencies and the incoherence of geocentric astronomy motivated him and eventually led him to propose the motions of Earth and of all the planets around the sun. His detailed effort to construct a planetary, heliostatic system with Earth in motion around the Sun may be seen properly as having inaugurated a revolution in cosmology. The resulting astronomical system, however, remained conservative, largely dependent on Ptolemy and other geocentric mathematical astronomers for the construction of models that were designed to preserve the ancient axiom regarding the perfectly uniform, circular motions of the heavenly bodies. This postscript focuses on revisions to Copernicus’s biography and to accounts of his education, books that he owned or used, path to the heliocentric theory, and his revision and adaptation of Aristotelian natural philosophy to heliocentrism.

Accounts of His Education . The details of Copernicus’s biography have undergone some revision although accounts of his life sometimes have been held hostage to the provincial or nationalistic sentiments of some contemporaries and later scholars. Still, such biases motivated biographers to search for documents that have contributed to a fuller picture of his life and work. There is little doubt now that Copernicus’s principal vernacular language was German, the commercial language of many of the towns along the Vistula River. The records of his administrative duties in Varmia in northeastern Poland suggest, however, that he knew more Polish than earlier experts were willing to concede. On some occasions, he may even have served as an interpreter between German and Polish-speaking representatives to meetings involving diplomatic negotiations between officials of Varmia, the Polish crown, and the Teutonic Knights.

Such possibilities to the contrary notwithstanding, Copernicus wrote some letters and reports in German, and all of his works on astronomy in Latin with occasional remarks in Greek. He devoted much time and effort to mastering technical details of astronomy and learning Greek so that he could consult ancient authorities where Latin translations were either unavailable or unreliable. Educated in a scholastic-humanist environment, he perceived problems that he thought he could solve by discovering errors, removing inconsistencies, and constructing an alternative but equally competent mathematical system.

Scholars assume that Copernicus received an education in the liberal arts at Kraków, but they tend to be vague or incomplete about what such an education entailed. Like most medieval universities, Kraków required students to attend the equivalent of eight classes on logic including lectures and exercises. Aside from learning the technicalities of valid reasoning, students also received instruction in how to construct arguments and recognize fallacies. The university curriculum additionally placed great emphasis on natural philosophy by means of lectures on Aristotle’s treatises on physics and cosmology. Kraków was exceptional in offering extensive instruction on mathematical subjects with special emphasis on astronomy and astrology. There is no doubt that Copernicus learned the fundamentals of astronomy and geometry at Kraków, for while a student at the university (1491–1495) he purchased books containing the Alfonsine Tables and a copy of a Latin translation of Euclid’s Elements. Scholars also introduced humanism at Kraków in the fifteenth century, and influenced Copernicus to develop his interest in the examination of ancient astronomy and mathematics. Although Kraków was propitious for the learning of fundamentals, Copernicus recognized that he would be able to advance his interests and career further only by completing his studies in Italy.

His uncle, the Bishop of Varmia, helped to arrange an ecclesiastical position for Copernicus that would provide the income needed to study law at Bologna. When he went there in 1496, Copernicus met Domenico Maria Novara, an astronomer who had links to the great fifteenth-century humanist-astronomer Regiomontanus. According to one source, Copernicus resided with Novara and assisted him in his astronomical observations. While in Bologna, Copernicus also began to study Greek, a language that he learned primarily, however, by translating a collection of letters that a friend arranged to have published in 1509.

His Sources . By 1500 Copernicus evidently had completed his formal instruction in the law, and he visited Rome during the Jubilee Year. He gave a lecture on mathematics, but unfortunately nothing is known about the details. He returned briefly to Varmia in 1501 to obtain permission to study medicine for two years. Copernicus went to the University of Padua where he evidently concentrated on that part of the curriculum concerned with practical medicine, especially diagnosis and the preparation of drugs. He left Padua without a degree, for which he would have required a third year. It was probably during those last two years that he acquired many of the books that he later used in Varmia. With his permitted time about to elapse, he went to the University of Ferrara in 1503, where two professors at the university prepared him for an examination in canon law. Copernicus passed the examination on the first try, returned to Varmia with his doctorate in canon law, and almost immediately joined the retinue of his uncle at the episcopal residence in Lidzbark Warmi ski. He remained there until 1510.

During those seven years Copernicus found the time to work his way through several of the books that he had purchased in Italy, and also consulted books in the collection of the episcopal library. The most important by far was Regiomontanus’s Epitome of Ptolemy’s Almagest. Relying on Cardinal Bessarion’s defense of Plato, Giorgio Valla’s encyclopedia, Pliny’s Natural History, and other works, Copernicus undertook the study that led him, probably around 1508 or 1509, to the heliocentric cosmology and his first sketch of the system, the Commentariolus, completed by 1514 at the latest.

Understanding His Cosmology . Copernicus’s path to a heliocentric cosmology is a matter of speculation. Some scholars believe that a mathematical analysis of models and technical details led him to his theory. Others believe that more qualitative and relatively less technical considerations led him to the conclusion that the celestial spheres of ancient Aristotelian cosmology and ancient astronomy could be ordered uniformly only by imagining Earth with its Moon in motion around the Sun. Transforming that solution into a technically competent system required several decades to accomplish, and the final results were not altogether satisfactory.

Whichever scenario one prefers, everyone agrees that Copernicus depended heavily on his predecessors, astronomical tables, Regiomontanus, Giorgio Valla, and, after 1515, Ptolemy’s own book in a printed Latin translation with its observations to accomplish his reformation or restoration of ancient astronomy. The principal goal or task of that tradition was to construct models that preserved the perfectly uniform, circular motions of the celestial spheres while agreeing with the observations within the then limits of accuracy. The goal, it turns out, was unachievable. That fact to the contrary notwithstanding, Copernicus’s effort persuaded Michael Mästlin, Johannes Kepler, and Galileo Galilei, among others, that his cosmological solution was correct. This conviction spurred them to complete what Copernicus had begun.

The details, of course, fascinate experts. For purposes of clarification and accuracy, it is necessary to distinguish between Copernicus’s vision and astronomers’ modern understanding. Copernicus accepted the ancient idea that planets are attached to or embedded in spheres. They do not float through space. The spheres support, contain, and move the planets. He was silent on the separate questions about the nature of the spheres and whether or not they are solid or hard. Spheres or orbs were considered to be three-dimensional bodies (whatever their nature), and so were solid in the same abstract sense in which any three-dimensional body is said to be a solid, but Copernicus did not elaborate. By assuming celestial spheres as the carriers of the planets, Copernicus committed himself to some features of Aristotle’s conception of the heavens. He knew that he had to justify his departures from Aristotle, which he did by constructing a number of arguments that relied on standard techniques of medieval logic and on other ancient authors, especially Pliny, Cicero, and a Greek dictionary known as the Suidae lexicon.

Some later authors were persuaded by such arguments, but for about a century most could not overcome the arguments based on common sense, and so they judged his theory to be absurd. The principal objections were physical. How is it possible for Earth to move so rapidly and its motion be insensible and imperceptible?

His Motivation . What motivated Copernicus to discover and then propose an idea that he could expect nearly everyone to reject? There are generally two approaches to this question, as briefly mentioned above. Some distinguish between Copernicus’s cosmological theory and his technical, mathematical system. According to the first, numerous inconsistencies in the ancient-medieval astronomical-cosmological tradition troubled Copernicus. For example, why are the planets arranged around Earth

according to two different principles? Mercury and Venus move with the Sun, and so both have a zodiacal period of one year. This fact also supported three alternative orderings of Mercury and Venus—between Earth and the Sun (Ptolemy), around the Sun (Martianus Capella), and beyond the Sun (Plato). Mars, Jupiter, and Saturn were placed beyond the Sun in that order, according to their sidereal periods. On this reading, Copernicus assumed that the planets should be ordered according to one principle. The Capellan arrangement probably inspired him to consider ordering all of the planets around the Sun, placing Earth with its Moon in orbit to fill the large gap between Venus and Mars. His calculation of the sidereal periods of Mercury and Venus would have confirmed their ordering, thus working out a unique arrangement of all of the planets ordered according to a single principle, sidereal periods.

Those who favor the second approach point to the fact that Copernicus was working with mathematical models and studying Regiomontanus’s Epitome. Among Copernicus’s books (now mostly at Uppsala University Library) is a codex that contains notes, tables, and the results of calculations in Copernicus’s own hand. One set of numbers in particular provides clues about how Copernicus transformed Ptolemy’s geocentric models into the heliocentric ones found in Commentariolus. He may have been inspired by two propositions in the Epitome to recognize a geo-heliocentric and a strictly heliocentric conversion of Ptolemy’s models. On this reading, he would have rejected the geo-heliocentric alternative because it entails the intersection of the spheres of Mars and the Sun, an unacceptable alternative, and so would have settled on the heliocentric conversion. There seems to be little question in the early twenty-first century that Copernicus did rely on those two propositions in the Epitome to convert the models, but he may not have recognized that possibility until after he had already formulated the heliocentric theory. Unfortunately, his copy of the Epitome has disappeared.

His first effort with double-epicycle models for the planets and the Moon later gave way to the mature presentation in De revolutionibus. Earth orbited by the Moon on a double-epicycle circles the mean sun (eccentric to the true or apparent Sun). Each of the superior planets moves on a small epicycle around the center of Earth’s orbit, eccentric models describe the motions of the inferior planets. In addition, following Ptolemy, he also provided separate accounts for the motions of the planets in latitude. Many subsequent astronomers admired the mathematics and used the models without adopting Copernicus’s physical assumptions about the motions of Earth.

Copernicus and his genuine followers were convinced of the truth of his system for primarily four reasons. First, his arrangement of the planets yields a natural explanation for the observation of the bounded elongations of Mercury and Venus. Second, the motion of Earth explains the observation of the retrograde motions of all of the planets as an optical illusion. The third reason is the ordering of the planets around the sun according to sidereal periods; Copernicus was most proud of this result. The fourth, following on the third, is the ability to estimate the relative linear distances of the planets from the Sun, and in this respect the calculations based on Copernicus’s numbers are very close to the modern ratios.

The theory had disadvantages, of course. There were principally four. The first is the absence of a coherent physical theory to account for the motions of Earth. The second is the failure to observe stellar parallax, a consequence that should follow from Earth’s annual orbit but which is unobservable with the naked eye. The third includes a number of mathematical weaknesses, such as problems with the measurement of the Sun’s eccentricity, the need to use epicycles, and the construction of models that contain a hidden equant. Finally, the heliocentric theory contradicted some passages of the Bible literally interpreted. For one or all of these reasons, most astronomers and philosophers rejected the theory for several decades.

His Ideas in Natural Philosophy . Scholars also disagree about Copernicus’s ideas in natural philosophy. What he says is very sketchy, making it necessary to reconstruct his intentions. Some believe that he merely revised Aristotelian principles, adapting them to heliocentrism. Others have demonstrated his reliance on other ancient authorities, and argue that his views derive from Neopla-tonic and Stoic sources. Copernicus’s arguments in De revolutionibus, Preface and Book I, seem intended to persuade Aristotelians to reexamine their assumptions about the simple motions of simple natural elemental bodies, and to recognize that several problems remained unsolved. For that reason some scholars, while acknowledging that Copernicus relied on Neoplatonic and Stoic sources, believe that he used them in conjunction with his reading of Aristotle, and perhaps scholastic commentaries reported and developed at Kraków, to fashion a sketchy account that was sufficiently and superficially Aristotelian enough to allay the anticipated rejection. The strategy failed in part because of a “Letter” added anonymously by Andreas Osiander right after the title page. Osiander advocated a strictly mathematical interpretation of the hypotheses and rejection of any physical interpretation.

For several decades many readers believed that Copernicus himself wrote the “Letter.” Whatever Osiander’s intention may have been, many astronomers found the approach congenial with their own views about astronomy and their equally firm conviction about a geocentric cosmos. It is impossible to say whether the strategy rescued Copernicus’s book and the theory from immediate and wholesale condemnation. His few supporters were spared official censure for several decades. Ironically, by the time church and theological authorities censured the work, evidence in support of the theory was growing. The publication of Kepler’s tables (1627) virtually assured that practicing astronomers would find it more difficult than before to separate the observational consequences from the models and hypotheses on which they were based, especially in Kepler’s corrected version of the heliocentric theory.

Whether Copernicus ever saw what Osiander had done is unknown. In 1543 when the book appeared he was near death, perhaps in a coma, when Rheticus brought a copy to him. Recent investigations by Polish scholars have also shed light on Copernicus’s death and burial. Excavation of the cathedral where he was buried has unearthed what the investigating scientists believe to be Copernicus’s remains. By means of forensic reconstruction they have generated an image of Copernicus’s head and face at the time of his death. By the mid-seventeenth century Copernicus became an icon for the lone scientist standing against what the world regards as common sense and for the courageous exercise of imagination in pursuit of the truth. In his own mind and words, he saw himself as having tried to restore and achieve the goals of ancient astronomy. Indeed, as an astronomer he was a conservative, but that cannot undo the fact, also contrary to his intention perhaps, that he introduced a revolution in cosmology that in turn contributed to the rise of modern science, a consequence that some refer to as the scientific revolution.

SUPPLEMENTARY BIBLIOGRAPHY

There are two modern editions of Copernicus’s works, one of which is also issuing parallel volumes with translations in several modern languages.

WORKS BY COPERNICUS

Locationes mansorum desertorum. Edited by Marian Biskup. Olsztyn, Poland: Pojeziere, 1970. Copernicus’s record of abandoned farmsteads in Varmia.

Three Copernican Treatises. Translated by Edward Rosen. 3rd ed., revised. New York: Octagon Books, 1971. Contains translations of Commentariolus, Letter against Werner, and Rheticus’s First Report(Narratio prima), and a biography of Copernicus with annotated bibliography.

Opera omnia. 4 vol. Vols. 1–2, and 4: Warsaw: Polish Scientific Publishers, 1973–1992. Volume 1 is a photographic copy of Copernicus’s manuscript. Volume 2 is the critical edition. Jerzy Dobrzycki completed the edition of Commentariolus for volume 3, but it has yet to appear in print. Volume 4 contains facsimiles of manuscripts of Copernicus’s minor works.

Nicolaus Copernicus Gesamtausgabe. 9 vols. Vols. 1–2, edited by Heribert M. Nobis and Bernhard Sticker. Hildesheim, Germany: H.A. Gerstenberg, 1974–1984. Vol. 3, edited by Heribert M. Nobis; vol. 5, edited by Heribert M. Nobis and Menso Folkerts; vol. 6, edited by Menso Folkerts; vols. 8–9, Berlin: Akademie Verlag, 1994–2004. The critical edition of Commentariolus will appear in volume 4. No information is available on volume 7. A brief historical summary of the project is available from http://www.geschichte.unimuenchen.de/wug/gnw/coped.shtml (in German).

On the Revolutions of the Heavenly Spheres. Translated by Alistair Matheson Duncan. New York: Barnes and Noble, 1976. Preferred by some experts over Rosen’s translation.

Complete Works. 4 vols. The first volume, as in the modern Latin editions, is a photographic copy of Copernicus’s manuscript. Vol. 2, On the Revolutions, edited by Jerzy Dobrzycki, translated by Edward Rosen with commentary. Warsaw: Polish Scientific Publishers; London: Macmillan, 1978. Also published Baltimore, MD, and London: Johns Hopkins University, 1978, reissued 1992. Vol. 3, Minor Works, edited by Pawe Czartoryski, translated with commentary by Edward Rosen and Erna Hilfstein. Warsaw: Polish Scientific Publishers; London: Macmillan, 1985. Reissued, Baltimore, MD, and London: Johns Hopkins University, 1992. Volume 3 contains Rosen’s revised translation of Commentariolus, and supersedes the translation in Three Copernican Treatises. The Commentariolus was also translated by Noel Swerdlow (1973) but embedded in a commentary for which it is primarily important. Vol. 4, The Manuscripts of Nicholas Copernicus’ Minor Works Facsimiles, edited by Pawe Czartoryski. Warsaw: Polish Scientific Publishers, 1992.

OTHER SOURCES

Birkenmajer, Aleksander. Études d’histoire des sciences en Pologne, Studia Copernicana, Vol. 4. Wroc aw, Poland: Polish Academy of Sciences, 1972. Articles and French translations of papers first written in Polish.

———. “Commentary.” In Nicolaus Copernicus, Opera omnia, Vol. 2. Warsaw: Polish Scientific Publishers, 1975. The authoritative Polish commentary written in Latin on Book I of De revolutionibus.

Birkenmajer, Ludwik Antoni. Mikołaj Kopernik. Kraków, Poland: Skad Gowny w Ksiegarni Spoki Wydawniczej Polskie, Skład Głóny w Księgarni Spółki Wydawniczej Poslkir, 1900. Materials toward a biography of Copernicus that Birkenmajer never wrote and that contains indispensable details and references. A partial and rough English translation was supervised by Jerzy Dobrzycki and Owen Gingerich (1976).

———. Stromata Copernicana. Kraków, Poland: Nakładem Polskiej adademji umiejętnosci, Nakładem Polskiej akademj iumiejętności, 1924. Another indispensable and somewhat more synthetic collection of chapters related to Copernicus’s education and works.

Biskup, Marian, ed. Regesta Copernicana. Translated by Stanis aw Puppel. Studia Copernicana, Vol. 8. Wrocław, Poland: Zaklad Naradovy, 1973. Chronology of documents related to Copernicus’s family and career. The English version adds a few documents to the Polish version.

———. “Biography and Social Background of Copernicus.” In Nicholas Copernicus, Quincentenary Celebrations, Final Report, edited by Zofia Ward ska. Studia Copernicana, Vol. 17. Wroc aw, Poland: Polish Academy of Sciences, 1977, pp. 137–152. Important reflections by a leading Polish historian.

Clutton-Brock, Martin. “Copernicus’s Path to His Cosmology: An Attempted Reconstruction.” Journal for the History of Astronomy 36 (2005): 197–216. Important review that amplifies Swerdlow’s analysis (1973).

Curtze, Maximilian. Reliquiae Copernicanae. Leipzig, Germany: B.G. Teubner, 1875. Important documents by one of the earliest Copernican scholars who examined the collection of Copernicana at Uppsala University Library.

———, ed. Mitteilungen des Coppernicus-Vereins für Wissenschaft und Kunst zu Thorn. Several volumes issued between 1878 and 1882 that contain editions and studies on Copernicus. Snabrück, Germany, 1878–1882.

Czartoryski, Paweł. “The Library of Copernicus.” Studia Copernicana (1978): 354–396. Indispensable foundational study of the books that Copernicus owned or used. Corrects many of Ludwik Birkenmajer’s attributions.

Di Bono, Mario. “Copernicus, Amico, Fracastoro and Tusi’s Device: Observations on the Use and Transmission of a Model.” Journal for the History of Astronomy 26 (1995): 133–154. Challenges the standard orthodoxy about Copernicus’s reliance on Arabic predecessors.

Dobrzycki, Jerzy. “Commentary.” In Nicolaus Copernicus, Opera omnia, Vol. 2. Warsaw: Polish Scientific Publishers, 1975. The authoritative Polish commentary written in Latin on Books II–VI of De revolutionibus.

Dobrzycki, Jerzy, and Owen Gingerich, eds. Nicholas Copernicus: Studies on the Works of Copernicus and Biographical Materials. Ann Arbor, Michigan: Bell and Howell Learning and Information (formerly University Microfilms International), 1976. Translation of several important chapters of Ludwik Birkenmajer’s Miko aj Kopernik.

Evans, James. The History and Practice of Ancient Astronomy. New York: Oxford University Press, 1998. Outstanding introduction to the field.

Fiszman, Samuel, ed. The Polish Renaissance in Its European Context. Bloomington: Indiana University, 1988. Important collection of papers, some of which are on Copernicus and his background.

Gąssowski, Jerzy, ed. Poszukiwanie Grobu Mikołlaja Kopernika, Castri Dominae Nostrae Litterae Annales. Vol. 2. Pułltusk, Poland: Baltic Research Center in Frombork, 2005. Results of most recent research on Copernicus’s burial place and on the forensic analysis of his presumed remains. For images of the reconstruction of Copernicus’s head and face, see http://archeologia.ah.edu.pl/Frombork_eng.html.

Gierowski, Józef, ed. The Kraków Circle of Nicholas Copernicus. Translated by Janina Ozga. Copernicana Cracoviensia, Vol. 3. Kraków, Poland: Jagiellonian University Press, 1973. Articles on Copernicus’s teachers and fellow students.

Gingerich, Owen. The Eye of Heaven: Ptolemy, Copernicus, Kepler. New York: American Institute of Physics, 1993. Studies on Copernicus and his reception.

———. “The Copernican Quinquecentennial and Its Predecessors.” In Commemorative Practices in Science: Historical Perspectives on the Politics of Collective Memory, edited by Pnina Abir-Am and Clark Elliott. Osiris, second series, 14 (1999): 37–60. A witty guide to the history of Copernican celebrations and scholarship through 1973.

———. An Annotated Census of Copernicus’ De Revolutionibus (Nuremberg, 1543 and Basel 1566). Leiden, Netherlands: Brill, 2002. Indispensable for studying the reception of the Copernican theory.

———. “Supplement to the Copernican Census.” Journal for the History of Astronomy 37 (2006): 232. Announces that Brill will issue a corrected reprint that will update some entries and add a total of twenty-two copies.

Goddu, André. “The Logic of Copernicus’s Arguments and His Education in Logic at Cracow.” Early Science and Medicine 1 (1996): 26–68.

———. “Copernicus’s Annotations—Revisions of Czartoryski’s ‘Copernicana.’” Scriptorium 58 (2004): 202–226, with eleven plates. Corrects Czartoryski (1978), provides a detailed description of Copernicus’s hand, proposes one addition to the authentic Copernicana, and verifies another.

———. “Hypotheses, Spheres, and Equants in Copernicus’s De revolutionibus.” In Les éléments paradigmatiques thématiques et stylistiques dans la pensée scientifique, edited by Bennacer el Bouazzati. Casablanca: Najah El Jadida, 2004, pp. 71–95. Attempts to resolve disputes among the experts.

———. “Reflections on the Origin of Copernicus’s Cosmology.” Journal for the History of Astronomy 37 (2006): 37–53. Orders the stages in Copernicus’s discovery.

Goldstein, Bernard. “Copernicus and the Origin of His Heliocentric System.” Journal for the History of Astronomy 33 (2002): 219–235. Important challenge to Swerdlow’s reconstruction (1973).

Hilfstein, Erna, ed. Starowolski’s Biographies of Copernicus. Studia Copernicana, Vol. 21. Wroc aw, Poland: Polish Academy of Sciences, 1980. Edition and study of early biographies.

Hipler, Franz, ed. Spicilegium Copernicanum. Festschrift des historischen Vereins für Ermland zum vierhundertsten Geburtstage des ermländischen Domherrn Nikolaus Kopernipus. Braniewo, Poland: Eduard Peter, 1873.

———. “Analecta Warmiensia.” Zeitschrift für die Geschichte und Altertumskunde Ermlands 5 (1874): 316–488. Indispensable edition and study of catalogs of Polish libraries from the fifteenth through the early seventeenth centuries.

Knoll, Paul. “The Arts Faculty at the University of Cracow at the End of the Fifteenth Century.” In The Copernican Achievement, edited by Robert S. Westman . Berkeley and Los Angeles: University of California Press, 1975, pp. 137–156.

———. “The World of the Young Copernicus: Society, Science, and the University.” In Science and Society, edited by Nicholas Steneck. Ann Arbor: University of Michigan, 1975, pp. 19–51.

Knox, Dilwyn. “Ficino, Copernicus and Bruno on the Motion of the Earth.” In Bruniana and Campanelliana, Richerche filosofiche e materiali storico-testuali 5 (1999): 333–366. Considers the sources for Copernicus’s doctrine of natural elemental motion.

———. “Ficino and Copernicus.” In Marsilio Ficino: His Theology, His Philosophy, His Legacy, edited by Michael Allen and Valery Rees. Leiden, Netherlands: Brill, 2002, pp. 399–418. Important article by the most authoritative scholar on Copernicus’s ancient and Renaissance sources.

Kokowski, Michał. Copernicus’s Originality: Towards Integration of Contemporary Copernican Studies. Warsaw and Kraków: Polish Academy of Sciences, 2004. Important attempt by a young Polish scholar to revise current historiography.

Kuhn, Thomas. The Copernican Revolution. Cambridge, MA: Harvard University Press, 1957. Accessible account that sparked a reevaluation of Copernicus’s achievement.

Markowski, Mieczysław. Filozofia przyrody w drugiej połowie XV wieku [Natural philosophy in the second half of the fifteenth century]. Dzieje filosofii redniowiecznej w Polsce [History of Medieval philosophy in Poland], Vol. 10. Wroc aw, Poland: Polish Academy of Sciences, 1983. The most important survey of the teaching on natural philosophy at the University of Kraków in the fifteenth century.

Moraux, Paul. “Copernic et Aristote.” In Platon et Aristote à la Renaissance. XVIe Colloque International de Tours. Paris: J. Vrin, 1976, pp. 225–238. Most thorough article to date on Copernicus’s acquaintance with the works of Aristotle.

Papritz, Johannes, and Hans Schmauch, eds. Kopernikus-Forschungen. Deutschland und der Osten, Vol. 22. Leipzig, Germany: S. Hirzel, 1943. Important materials related to Copernicus’s biography.

Prowe, Leopold. Nicolaus Coppernicus. 2 vols. Berlin: Weidmann, 1883–1884. Reprinted, Osnabrück, Germany: Zeller, 1967. Dated but still valuable biography with documents.

Rose, Paul. The Italian Renaissance of Mathematics. Geneva: Droz, 1975. Important for the humanistic background to Copernicus’s achievement, especially chapters 2–5.

Rosen, Edward. Copernicus and the Scientific Revolution. Malabar, Florida: Robert E. Krieger, 1984. Defends Copernicus’s role in the scientific revolution, and provides documents translated into English.

———. Copernicus and His Successors. London and Rio Grande, OH: Hambledon Press, 1995. Important collection of previously published articles.

Rosińska, Graýna. “Nicolas Copernic et l’école astronomique de Cracovie au XVe siècle.” Mediaevalia philosophica Polonorum19 (1974): 149–157. One of many important articles by a leading Polish scholar.

Schmeidler, Felix. Kommentar zu “De revolutionibus.” Volume 3/1 of Nicolaus Copernicus Gesamtausgabe, edited by Heribert M. Nobis. Berlin: Akademie Verlag, 1998. The standard German commentary.

Studia Copernicana. 37 volumes to date. Warsaw: Polish Academy of Sciences, 1970–1999. Contains several volumes on Copernicus as well as a subsidiary series titled Colloquia Copernicana. There is also a Brill’s series of Studia Copernicana, 2 volumes to date. Leiden, Netherlands, and Boston: Brill, 2002.

Swerdlow, Noel. “The Derivation and First Draft of Copernicus’s Planetary Theory: A Translation of the Commentariolus with Commentary.” Proceedings of the American Philosophical Society 117 (1973): 423–512. The commentary is authoritative.

———. “An Essay on Thomas Kuhn’s First Scientific Revolution, the Copernican Revolution.” Proceedings of the American Philosophical Society 148 (2004): 64–120. A contextual and positive evaluation of Kuhn (1957) that is illuminating and insightful about Copernicus’s achievement.

Swerdlow, Noel, and Otto Neugebauer. Mathematical Astronomy in Copernicus’s De Revolutionibus. 2 parts. New York: Springer Verlag, 1984. The most authoritative and thorough examination of Copernicus’s mathematics with a very important introduction.

Westman, Robert. ed. The Copernican Achievement. Berkeley and Los Angeles: University of California Press, 1975. Several important papers, including one by Westman on Wittenberg interpreters of Copernicus’s theory.

———. “The Melanchthon Circle, Rheticus, and the Wittenberg Interpretation of the Copernican Theory.” Isis 66 (1975): 165–193. One of Westman’s groundbreaking studies on the reception of the Copernican theory.

———. “The Astronomer’s Role in the Sixteenth Century: A Preliminary Study.” History of Science 18 (1980): 105–147. Emphasizes one claim made by Copernicus that can be regarded as properly revolutionary.

———. “Copernicus and the Prognosticators: The Bologna Period, 1496–1500.” Universitas 5 (1993): 1–5. Brief but suggestive summary of additional motives behind Copernicus’s reformation of astronomy.

Wyrozumski, Jerzy, ed. Das 500 jährige Jubiläum der krakauer Studienzeit von Nicolaus Copernicus. Kraków, Poland: Internationales Kulturzentrum, 1993. Important studies on Copernicus’s education.

Zinner, Ernst. Entstehung und Ausbreitung der copernicanischen Lehre, edited by Heribert Nobis and Felix Schmeidler. 2nd ed. Munich, Germany: C.H. Beck, 1988. Revised, corrected, and annotated version of Zinner’s important studies.

André Goddu

COPERNICUS, NICOLAUS

COPERNICUS, NICOLAUS (1473–1543), Polish cleric and astronomer, was born Mikołaj Kopernik in Torún, Poland, on February 19, 1473. He was raised in the comfortable circumstances of a wealthy burgher family and was educated at the cathedral school. Upon the death of his father in 1583, Copernicus and his younger brother Andreas were taken under the guardianship of their maternal uncle, Canon Lucas Watzenrode, who had been trained in the cosmopolitan humanist atmosphere of Bologna and later was made prince bishop of the Diocese of Warmia. Copernicus matriculated in the Collegium Maius of the renowned Jagiellonian University of Kraków, which at that time was strong in mathematics and had an endowed chair of astronomy dating from 1410. Copernicus's study of the theories of such luminaries as Ptolemy, Euclid, Sacrobosco, and Regiomontanus was complemented by his own observation in Kraków of the comets of 1491 and 1492 and of four lunar and solar eclipses during the next two years.

In 1496 Copernicus and his brother were sent to Bologna by their uncle to further their educations. During his decade in Italy, Copernicus studied medicine at Padua, continued his observations of the heavens, and became well enough versed in philosophy and classical literature to translate the letters of a Byzantine poet into Latin. In 1503 Copernicus took his degree in canon law from the University of Ferrara. Watzenrode had arranged for Copernicus's election to a benefice in the Diocese of Warmia to ensure his nephew's financial independence, and Copernicus returned to Poland to embark upon his duties as a canon of Frombork Cathedral. For the next four decades he was engaged in ecclesiastical administration and other service to the diocese. He wrote an important treatise on coinage, painted a self-portrait, and conscientiously practiced medicine. Astronomy remained his passion, however, and in 1510 he built a modest observatory in a tower near the cathedral.

Copernicus and Astronomy

In order to evaluate Copernicus's significance in relation to religion, one must first understand how he transformed astronomy. His enduring legacy was the rehabilitation of the long-neglected heliocentric hypothesis. The concept of a moving earth was not new of course, having been proposed in the third century bce by Aristarchus of Samos and discussed by Archimedes, although Philolaus and Ecphantus the Pythagoreans are the ancients whom Copernicus mentions in connection with the idea. But the ancient arguments against heliocentrism, both from common sense and from lack of observed stellar parallax, had been so overwhelming that the alternative geocentric cosmology prevailed from antiquity through the late Middle Ages.

Aristotle (384–322 bce) envisioned a set of nested concentric spheres bearing the planets, the sun, the moon, and the stars around a spherical, stationary earth. This system was enlarged and codified by the second-century Egyptian astronomer Ptolemy in the Almagest, which became the basic astronomical text of the scholastic canon. In order to preserve uniform circular motion while accounting for the periodic retrograde motion of the planets against the backdrop of the fixed stars, the system invoked a scheme of epicycles and eccentrics that revolved on the deferent circle about the equant point. Ptolemaic astronomy was integrated with Aristotelian physics in scholastic science, in which circular motion was proper to the heavens and rectilinear motion to the earth and in which the four terrestrial elements (earth, water, fire, and air) were disposed appropriately according to their degrees of levity or gravity. The pre-Copernican cosmology was in turn integrated with theology to form an orderly scholastic synthesis of physics, astronomy, and theology. Each science in this hierarchy of disciplines operated from its own set of principles, and together they governed everything from the nature of matter and planetary motion to the geographic location of heaven and hell.

By the sixteenth century Ptolemaic astronomy had begun to encounter difficulties in accurately predicting celestial phenomena. The system of eccentrics and epicycles revolving about the equant point "saved the appearances" in accounting for retrograde planetary movements without sacrificing uniform circular motion. But the minute inaccuracies of this system when compounded annually over more than a millennium had pushed astronomical reckoning off by ten days. This cumulative error posed serious calendrical problems, including the difficulty of correctly calculating the date of Easter, the central Christian feast on which much of the church year was based.

As Copernicus continued his quest for improving predictive accuracy in astronomy, he gradually turned his attention to the possibility of a moving earth, sketching his system in the Commentariolus. This unpublished outline circulated widely in draft form among his students before 1514 and challenged established tradition by proposing three kinds of terrestrial motion: (1) real diurnal rotation of the earth to account for the apparent diurnal rotation of the heavens; (2) annual revolution about the stationary sun to account for the solar year; and (3) motion in declination to account for the precession of the equinoxes.

Copernicus continued to elaborate his planetary theory during the next quarter century. In 1539 a Lutheran scholar from Wittenberg named Georg Joachim Rheticus (1514–1574) learned of Copernicus's theory and traveled to Frombork to study it in detail with the Catholic astronomer. He became Copernicus's first disciple, published his own sketch of the system, Narratio Prima, in 1540, and finally persuaded Copernicus to offer his theory to the world. The latter in 1541 authorized Rheticus to carry a copy of the manuscript to Nuremberg, where it was published by Johannes Petreius under the title De revolutionibus orbium coelestium libri sex (1543). As circumstances did not permit Rheticus to remain in Nuremberg to oversee publication, that duty was entrusted to the Lutheran theologian Andreas Osiander (1498–1552), who added an unauthorized preface stating, "These hypotheses need not be true nor even probable; if they provide a calculus consistent with the observations, that alone is sufficient." Osiander emphasized the hypothetical nature of astronomy used as a calculating device, apparently for the purpose of protecting the work from overzealous censors. But whether or not Copernicus was aware of this preface when De revolutionibus was presented to him in 1543 as he lay dying, he almost certainly would not have agreed with Osiander's disclaimer that heliocentrism should be treated as a mathematical convenience rather than as a genuine claim about the true physical nature of the cosmos.

De revolutionibus sits in the paradoxical position of being on the one hand essentially a conservative work in the classical tradition of astronomy and on the other hand a book that sparked a major revolution in scientific thought. With the exception of an engaging broad exposition of the system in the first of its six books, De revolutionibus is a highly mathematical treatise that made few initial converts. Although it was widely read in astronomical circles, fewer than a dozen committed Copernicans before 1600 can be identified.

As a conservative reformer, Copernicus preserved the assumption of uniform circular motion and continued to employ Ptolemy's epicycles and eccentrics. Indeed he has been referred to as the last great Ptolemaic astronomer. Where he departed from the tradition of Ptolemy was in pursuing the insight that shifting the reference frame from the earth to the sun not only increased observational accuracy but for the first time made logical sense out of the order of the planets. Rather than viewing the sun, moon, and planets with their varying dimensions as arbitrarily assigned to widely divergent periods and orbital angles, a heliocentric system generated an intrinsic order. The planets farthest from the sun had the longest orbital periods and the widest orbital angles, while those closest to the center revolved most tightly and rapidly around the sun. Likewise the Copernican model also made coherent sense of retrograde motion. Instead of interpreting the looping paths of the planets against the sidereal backdrop as actual celestial occurrences, Copernicus understood these motions to be mere optical illusions resulting from the annual revolution of the terrestrial observatory inside or outside the orbits of its fellow planets. Copernicus offered a remarkably prescient rebuttal to Ptolemy's objection that a moving earth would leave any loose objects drifting westward. He suggested two possible explanations, one based on an Aristotelian mingling of qualities and another on the idea of momentum: "The reason may be either that the nearby air, mingling with earthy or watery matter, conforms to the same nature as the earth, or that [this] air's motion, acquired from the earth by proximity, shares without resistance in its unceasing rotation" (DR I.8).

Astronomers appreciated the increased predictive accuracy of Copernicus's system, although initial reaction to his revolutionary postulate was guarded. More significantly the fruitfulness of his effort may better be measured by the range and diversity of theories he stimulated. De revolutionibus gave free rein to an incremental rethinking of astronomy and physics that challenged the existing hierarchy of disciplines and that within a century blossomed into a full-scale scientific revolution. Ptolemaic astronomy no longer offered a satisfactory architectonic vision of the cosmos, and Copernicus was not the only thinker prepared to suggest an alternative model. The Danish astronomer Tycho Brahe (1546–1601) proposed a "geo-heliocentric" model in which the five planets revolve around the sun, which in turn revolves with the moon around the earth. Brahe appreciated Copernicus's success in circumventing the most discordant aspects of the Ptolemaic system, but he personally could not overcome a revulsion of ascribing to the sluggish earth the quick motion shared by the "ethereal torches." But Brahe did initiate a break with the Aristotelian assumption of celestial immutability when he claimed that the nova of 1572 was in fact a new star and when he concluded that, because the comet of 1577 looped around the sun in an orbit closer than that of Venus, there could be no crystalline spheres.

Copernicus and Brahe inhabited a pre-Newtonian, predynamical age, and their respective modifications of geocentrism remained committed to uniform circular motion as a perfection proper to the heavens. A more remarkable departure from classical astronomy was initiated by Brahe's student Johannes Kepler (1571–1630), whose close observation of Mars led him to postulate elliptical planetary orbits with the sun occupying one focus of the ellipse. The psychological impact of this "breaking of the circle" was arguably a challenge greater even than the shift to heliocentrism, and the introduction of a dynamic element was a significant step on the path to the eventual Newtonian synthesis.

Further challenges unfolded with the telescopic observations of Galileo Galilei (1564–1642). Galileo's publication of Sidereus nuncius (1610) provided physical evidence that seemed to confirm the mathematical theory of heliocentrism, although genuine empirical proof of the earth's annual orbital motion only arrived with Friedrich Wilhelm Bessel's (1784–1846) establishment of stellar parallax in the 1830s and the confirmation of diurnal axial rotation awaited Jean-Bernard-Léon Foucault's (1819–1868) pendulum in 1851. Nevertheless Galileo's charting of the revolutions of the moons of Jupiter and the phases of Venus suggested, by analogy, the plausibility of the heliocentric cosmological model. Likewise his observation of lunar craters implied the similarity of the moon to the earth, and his discovery of sunspots furthered the argument that mutability is not confined only to the terrestrial realm.

Reactions to Copernicus's Theory

The fortunes of the Copernican hypothesis were shaped not only by its incremental scientific acceptance but also by factors such as the flexibility of intellectual culture and the circumstances of ecclesiastical politics. Since the Condemnations of 1277 the church had wisely refrained from committing itself to a single cosmological model, and Nicole d'Oresme (c. 1325–1382), bishop of Lisieux, had felt free to consider a number of arguments for diurnal rotation in his 1377 commentary on Aristotle's De caelo. Copernicus himself dedicated De revolutionibus to Pope Paul III, and the immediate response on the part of the post-Tridentine church was such that no particular restrictions were imposed on Catholic astronomers. However, whereas the Counter-Reformation was not in itself antiscientific, it was certainly not about to embrace innovations that would undermine its dogmas. One consequence of this was the papal mandate to carry out policies of the Council of Trent (1545–1563), including reinforcing exegesis that emphasized wherever possible the literal interpretation of the Bible.

Moreover astronomical speculation could also carry heterodox implications, as in the case of Giordano Bruno (1548–1600), who postulated a plurality of worlds and the infinity of the universe. Although Bruno was executed for theological heresy rather than for his scientific views, he was a vehemently anti-Aristotelian admirer of Copernicus, and from the 1590s astronomical innovation became associated with heterodoxy. In the decades after the Council of Trent the Catholic Church entered what William Shea has referred to as a period of restrictive orthodoxies in which Aristotelianism became applied as a mechanical criterion of the truth. In such an atmosphere it is not surprising that the initially favorable reception of Galileo's telescopic discoveries should have been accompanied by suspicion of his Copernicanism and ultimately by the suspension of De revolutionibus, "until corrected," by the Congregation of the Index in 1616. This suspension was honored mostly in the breach, and Owen Gingerich has shown that only about 8 percent of the five hundred extant copies of the first edition were censored by their owners in full compliance with the index.

Copernicus's deceptively simple insight in De revolutionibus carried with it enormous implications for a wide range of disciplines and questions. In physics and astronomy it played an important role in initiating the process of scientific discovery that has led from Kepler and Galileo through Sir Isaac Newton (1642–1727) and Pierre-Simon de Laplace (1749–1827) to the twenty-first century. In epistemology the Copernican revolution upset the established order of the scholastic curriculum by daring to use mathematics, a lower science, to correct astronomy, a science of higher dignity. An extension of this epistemological challenge was Galileo's elevation of sense experience—in the form of experiment and observation—into a more important role than it had enjoyed under Scholastic Aristotelianism.

Copernicus and his successors also contributed to the secularization of modernity through the disenchantment of cosmology, the removal of the earth from its central location, and the relativization of human concerns by contrast with the infinity of time and space. Copernicus contended that the size of the universe was "similar to the infinite." Theologically an intriguing swing occurred from the church's relative neutrality on cosmology before Copernicus to its rigid adherence to the Aristotelian-Ptolemaic worldview during the Galileo affair and back again to a relative independence from cosmological commitment. Although theology cannot remain wholly apophatic about the world in which it is embedded, too close an adherence to a particular worldview will leave the believer high and dry when the paradigm changes, as inevitably it will. From a modest and relatively self-contained pre-Copernican cosmos focused on the human drama of salvation, scholars have moved to a vast and much less obviously anthropocentric universe. In Copernicus's prophetic words, "So vast, without any question, is the divine handiwork of the most excellent almighty" (DR I.10).

See Also

Galileo Galilei; Kepler, Johannes; Newton, Isaac; Ptolemy.

Bibliography

Copernican studies were enriched with numerous publications surrounding the quincentenary of the astronomer's birth in 1973. The English translation of Copernicus's writings is Nicolaus Copernicus, Complete Works, 3. vols. (London, 1972–1992). Edward Rosen, translator, Three Copernican Treatises, 3d ed. (New York, 1971), includes an accessible Commentariolus and supporting materials. Concise biographical sketches include Wanda M. Stachiewicz's Copernicus and His World (Montreal, 1972); and Jan Adamczewski's nicely illustrated Nicolaus Copernicus and His Epoch (Philadelphia, 1972). Many of Rosen's meticulous examinations of specific details are in his Copernicus and His Successors (London, 1995).

A classic account of Copernicus's astronomical science in a traditional "revolution" context is Thomas S. Kuhn's The Copernican Revolution (Cambridge, Mass., 1957). See also Rosen, Copernicus and the Scientific Revolution (Malabar, Fla., 1984). Noel M. Swerdlow and Otto Neugebauer provide a detailed analysis in Mathematical Astronomy in Copernicus's "De revolutionibus" (New York, 1984), which includes a definitive biographical study by Swerdlow. Various features of Copernicus's science are treated in Owen Gingerich's The Eye of Heaven: Ptolemy, Copernicus, Kepler (New York, 1993).

Kenneth J. Howell examines the reception of Copernicanism in light of scriptural exegesis in God's Two Books: Copernican Cosmology and Biblical Interpretation in Early Modern Science (Notre Dame, Ind., 2002). For an important study of Protestant and Catholic attitudes to Copernicanism before Galileo, see Robert S. Westman, "The Copernicans and the Churches," in God and Nature: Historical Essays on the Encounter between Christianity and Science, edited by David C. Lindberg and Ronald L. Numbers (Berkeley, Calif., 1986). James M. Lattis shows the importance of the Jesuit influence in Between Copernicus and Galileo: Christoph Clavius and the Collapse of Ptolemaic Cosmology (Chicago, 1994).

Indispensable to the study of the early fortunes of the heliocentric hypothesis is Gingerich's An Annotated Census of Copernicus' "De revolutionibus" (Nuremberg, 1543, and Basel, 1566) (Leiden and Boston, 2002), an examination of over six hundred extant copies of Copernicus's book. Gingerich recounts this quest as an engaging intellectual adventure in The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus (New York, 2004).

Peter M. J. Hess (2005)

COPERNICUS, NICOLAUS (1473–1543)

COPERNICUS, NICOLAUS (1473–1543), Polish astronomer, born in Thorn (Torun), West Prussia, a province subject to the king of Poland. In about 1485, after his father's death, Nicolaus came under the care and patronage of his maternal uncle, who shortly afterward became bishop of Varmia (Ermland).

EDUCATION AND CAREER

Beginning in 1491, Copernicus enrolled successively at the universities of Cracow, Bologna, and Padua, where he studied, respectively, mathematics and astronomy, canon and civil law, and medicine. He was elected a canon of the cathedral chapter of Varmia in 1497, providing him with a lifetime income. In 1503 he was awarded a doctorate in canon law from the University of Ferrara.

In 1610 Copernicus settled in Frauenburg (Frombork), near the Baltic Sea. There he carried out his canonical duties, practiced medicine, administered the holdings of the Varmia chapter, wrote on the problem of the debasement of the silver coinage of Royal Prussia, and continued to work intensively at improving the astronomical ideas he had begun to develop earlier.

As a student, Copernicus had become aware of the dichotomy between Aristotelian principles and the techniques employed by Claudius Ptolemy (c. 100–c. 170), the greatest astronomer of antiquity. For Aristotle (384–322 b.c.e.) the motionless Earth at the center of the universe was surrounded by uniformly rotating homocentric spheres carrying the Moon, Sun, and planets. The task of astronomy was to devise geometrical means for calculating the apparent positions of the celestial bodies, which neither moved uniformly nor maintained a constant distance from Earth. The planets, moreover, periodically moved with retrograde motion.

Some time after 1502, Copernicus circulated among a few individuals an anonymous treatise, subsequently titled Commentariolus (Brief commentary), an early stage in the development of his heliocentric system. He shortly afterward began De revolutionibus (On the revolutions), his detailed exposition of this system.

In 1539 Georg Joachim Rheticus (1514–1574) of the University of Wittenberg visited Copernicus. Impressed by Copernicus's theory, Rheticus tested the waters for the publication of Copernicus's almost completed work by publishing in 1540 his own account of it, Narratio prima (First account). Its reception encouraged Copernicus to publish his own work, a copy of which reached Copernicus as he lay dying in 1543.

Andreas Osiander (1498–1552), a Lutheran minister, oversaw the printing of the latter part of Copernicus's book and inserted an anonymous preface asserting, contrary to Copernicus's opinion, that the work represented only calculating devices and not the true constitution of the universe.

THE COPERNICAN SYSTEM

Copernicus's heliocentrism possessed several advantages over Ptolemaic astronomy. The apparent retrograde motions of the planets could now be accounted for by the revolution of Earth, dispensing with Ptolemaic astronomy's traditional geometric devices. Copernicus eliminated the Ptolemaic equant, a point not at the center of Earth about which the planets moved uniformly, and substituted a technique earlier used by a Muslim astronomer. Corrections to the apparent distances of the Moon also had Arabic roots. The relative distances of the planets from the Sun could now be determined as fractions or multiples of the distance from Earth to the Sun. Above all, Copernicus had created an integrated astronomical system, contrary to the independent sets of geometrical techniques for each of the planets characteristic of Ptolemaic astronomy. This was undoubtedly the prime consideration for the creation of his system.

Despite its advantages, heliocentrism was not without physical, observational, and theological problems. A revolving and rotating Earth violated several long-established Aristotelian principles, including the tendency of dropped bodies to fall to Earth at the center of the universe. Copernicus held that bodies fell because they tended to rejoin the spherical bodies of which they had been a part. For the Peripatetics, objects on a rotating Earth would be flung off, and objects thrown aloft should then land to the west of the point from which they were thrown. Copernicus responded that bodies on Earth or above it share in its circular motion. To the charge that observations made from an orbiting Earth should show stellar parallax, a change in the apparent position of the stars in the course of a year, Copernicus answered that a parallax could not be observed because the stars were much farther than had been believed.

RECEPTION AND INFLUENCE

In 1551 Erasmus Reinhold (1511–1553) published the Tabulae Prutenicae (Prutenic Tables) based on Copernicus's work. They were more accurate than the tables commonly in use, and they helped sustain interest in the Copernican theory. In particular, astronomers at the University of Wittenberg thought the Copernican theory was superior to that of Ptolemy in a number of respects, but they did not accept its heliocentrism. Throughout Europe a few astronomers were open to the validity of Copernicanism's fundamental hypothesis, but hardly any accepted it fully.

However, successive challenges to Aristotelian concepts, based on precise observations, began to remove some objections to Copernicanism. Tycho Brahe (1546–1601), whose astronomical observations were more accurate than any previously recorded, rejected heliocentrism, as did a few others, in favor of a geoheliocentric system, in which the planets circled the Sun, while the Sun revolved about the motionless Earth. Johannes Kepler (1571–1630), using Brahe's data, modified Copernicus's system significantly in 1609. Kepler placed the Sun in one of the foci of each of his elliptical planetary orbits, which were traversed with non-uniform motion. This led to a significant improvement in the prediction of planetary positions.

Galileo Galilei's (1564–1642) observations with the telescope beginning in 1609, as well as his subsequent publications on the nature of motion, were most important in the removal of Aristotelian objections to a moving Earth and to the size of the solar system. The placing of Copernicus's De revolutionibus on the Index of Prohibited Books in 1616 and Galileo's subsequent trial for heresy had little effect. With the work of Kepler and Galileo, as well as the influence of Cartesianism, heliocentrism became increasingly accepted; most astronomers were won over by the middle of the seventeenth century.

Copernicanism marked a turning point in the history of astronomy and provided a foundation for the remarkable achievements in related sciences in the seventeenth century. Copernicus's heliocentrism played a significant role in debates about the cause of planetary motion, and the nature of space, matter, and motion, and was thus a significant component of and stimulus to the scientific revolution.

See also Astronomy ; Brahe, Tycho ; Cartesianism ; Galileo Galilei ; Index of Prohibited Books ; Kepler, Johannes ; Scientific Revolution .

BIBLIOGRAPHY

Primary Sources

Copernicus, Nicolaus. Copernicus: On the Revolutions of the Heavenly Spheres. Translated by A. M. Duncan. Newton Abbot and New York, 1976. Translation of De revolutionibus orbium coelestium, 1543.

——. Three Copernican Treatises: The Commentariolus of Copernicus, The Letter against Werner, The Narratio Prima of Rheticus. Translated with an introduction by Edward Rosen. 3rd rev. ed. New York, 1971.

Secondary Sources

Armitage, Angus. Copernicus: The Founder of Modern Astronomy. New York and London, 1957. A general survey in the context of the history of astronomy.

North, John. "Copernicus' Planetary Theory." In The Norton History of Astronomy and Cosmology. Chapter 11. New York and London, 1995. A brief survey for the general reader.

Swerdlow, Noel M., and Otto Neugebauer. Mathematical Astronomy in Copernicus's De Revolutionibus. 2 parts. Berlin and New York, 1984. Has a substantial nontechnical introduction, including biographical details and the development of Copernicus's ideas.

Wilbur Applebaum

Nicolaus Copernicus

February 19, 1473
Toruń, Poland
May 24, 1543
Formbork, Poland

Theologian and astronomer

"In the center rests the sun. For who would place this lamp of a very beautiful temple in another or better place than this wherefrom it can illuminate everything at the same time."

Nicolaus Copernicus as quoted in Nicholas Copernicus on the Revolutions edited and translated by Edward Rosen.

The Polish theologian and astronomer Nicolaus Copernicus (1473–1543) is credited with starting the scientific revolution in 1543 by publishing De revolutionibus orbium coelestium (On the revolutions of the heavenly orbs). In this work he proposed that the Sun, not the Earth, is the center of the universe. Although the book received little attention at the time, Copernicus's theory later caused considerable controversy. Not only did it contradict the accepted ideas of ancient astronomers, but it also challenged the teachings of the Roman Catholic Church. In the early 1600s the Italian astronomer Gailileo (1564–1642; see entry) used Copernicus's observations to formulate his own proof of a Sun-centered universe, unleashing a confrontation with the church that lasted into the late twentieth century.

Pursues interest in astronomy

Nicolaus Copernicus had a life-long career as a canon (clergyman at a cathedral) in the Roman Catholic Church, pursuing the study of astronomy (the study of celestial bodies, such as planets, stars, the Sun, and the Moon) in his spare time. He was born on February 19, 1473, in Toruń, Poland, about one hundred miles south of Danzig (now Gdańsk). He belonged to a family of merchants. His uncle, the bishop and ruler of Ermland, Poland, was the person to whom Copernicus owed his education, career, and security. Copernicus graduated from the University of Cracow in Poland 1494. Although he did not attend any classes in astronomy, he began to collect books on astronomy and mathematics during his student years. In 1496 Copernicus set out for Bologna, Italy, to study canon (church) law. In Bologna, he came under the influence of the astronomer Domenico Maria de Novara (1454–1504) and recorded the positions of some planets. He did the same in Rome, where he spent the Jubilee Year of 1500. (Jubilee is a time of special solemnity declared by the pope, head of the Roman Catholic Church, every twenty-five years.)

In 1501 Copernicus made a brief visit to Frauenburg. His first official act as canon was to apply for permission to spend three more years in Italy, which was granted him on his promise that he would study medicine. Copernicus settled in Padua, but later he moved to the University of Ferrara, where he obtained the degree of doctor in canon law in 1503. Only then did he take up the study of medicine in Padua, prolonging his leave of absence until 1506. Upon returning to Ermland, Copernicus stayed in his uncle's castle at Heilsberg as his personal physician and secretary. During that time he translated from Greek into Latin the eighty-five poems of the seventh-century Byzantine poet Theophylactus Simacattes (died after 640). The work was printed in Cracow in 1509.

Formulates controversial theory

At this time Copernicus was also mulling over the problems of astronomy, especially the heliocentric (Sun-centered) system. He outlined the system in a short unpublished manuscript known as the Commentariolus (Small commentary), which he completed around 1512. Copernicus himself referred to this work as "Sketch of Hypotheses Made by Nicolaus Copernicus on the Heavenly Motions." Copies of the manuscript circulated among his friends, who were eager to know about his ideas. At the outset of Commentariolus, Copernicus listed seven axioms (statements accepted as being true), each of which stated a feature of the heliocentric system. The third and most controversial axiom stated that since all planets revolve on orbits around the Sun, the Sun must therefore be the center of the universe. This idea was controversial because astronomers at the time accepted the theory of the ancient Egyptian scholar Ptolemy (also known as Claudius Ptolemaeus; c. a.d. 100–c. 170), who concluded that the Sun revolved around the Earth.

Ptolemy presented his views on the heavens in the Almagest, which covered all aspects of mathematical astronomy (study of heavenly bodies through mathematical calculations) as it was understood in antiquity. To attain knowledge of the universe, Ptolemy argued, one must study astronomy because it leads to the Prime Mover (God), the first cause of all heavenly motions. Ptolemy followed earlier Greek thinkers such as Aristotle (384–322 b.c.), who believed that the Earth is the center of a fixed and perfectly balanced universe. Ptolemy argued that the universe has a spherical (round) shape and that stars and planets move in circular patterns. He also contended that the Earth is spherical and remains in a fixed position at the center of the universe. However, the Earth's size is insignificant in comparison to that of the heavens. According to Ptolemy, all heavenly bodies rotated around the Earth in larger and larger circles that shared approximately the same center point. The order of the circles was, first, the Moon, then Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and the last sphere of the fixed stars. Ptolemy's view was enforced by the Catholic Church, which found supporting evidence in the Bible (the Christian holy book).

In Commentariolus Copernicus proposed a system in which the Sun replaced the Earth at the center of the universe, and the Earth was moved to take the place of the vacated Sun. Copernicus stated that the heavens (planets and stars) do not actually rotate. They only appear to do so because the Earth makes a daily rotation on its own axis (an imaginary line that extends through the center of the globe from north to south). Similarly, the Sun appears to rotate along a path around the Earth only because the Earth makes an annual rotation around the Sun. The motions of the planets are also merely reflections of the Earth's travel in its orbit.

Turns astronomy "upside down"

Commentariolus produced no reaction, either in print or in letters, but Copernicus's fame began to spread. In 1514 he received an invitation to be present as an astronomer at the Fifth Lateran Council in Rome, a church conference that had as one of its aims the reform of the calendar. He did not attend. His secretiveness only seemed to enhance his reputation. In 1522 the secretary to the king of Poland asked Copernicus to give an opinion on De motu octavae spherae (On the motion of the eighth sphere), which had just been published by Johann Werner, a respected mathematician. This time Copernicus responded in a letter expressing a rather low regard for Werner's work. Copernicus also stated that he was writing his own study on the motion of the stars. He could pursue his scientific work only in his spare time, however, because his responsibilities as a canon kept him busy. He was involved in various aspects of the church, including legal and medical matters, but especially administrative and financial functions. In fact, he composed a booklet in 1522 on the remedies of inflation (increase in prices), which then largely meant the preservation of the same amount of gold and silver in coins. Although Copernicus did not publish anything about astronomy and had no contact with other astronomers, rumors continued to circulate about the revolutionary nature of his heliocentric theory.

Not all the comments were flattering. The Protestant reformer Martin Luther (1483–1546; see entry) denounced Copernicus for foolishly trying to overturn established theories of astronomy. In 1531 a satirical play was produced about Copernicus in Elbing, Prussia, by a local schoolmaster. In Rome things went better. In 1533 John Widmanstad, a secretary of the pope, lectured on Copernicus's theory before Pope Clement VII (1478–1534; reigned 1523–34) and several cardinals (church officials who rank directly below the pope). Three years later Cardinal Nikolaus von Schönberg wrote Copernicus a letter, urging him to publish his thoughts. It was a futile request. Probably nobody knew exactly how far Copernicus had progressed with his work until Georg Joachim Rheticus (1514–1576), a young scholar from Wittenberg, Germany, arrived in Frauenburg in 1539.

In 1540 Rheticus printed a summary of Copernicus's nearly completed book, De revolutionibus orbium coelestium (Revolutions of the heavenly spheres). The summary was known as the Narratio prima (First report). Two years later Rheticus was instrumental in having a portion of the book published in Nuremberg. When he took a position at the University of Leipzig, the publication process was taken over by Andreas Osiander (1498–1552), a Lutheran clergyman. Osiander worked with an editor at the printing press. Osiander might have been the one who gave the work its title, De revolutionibus orbium coelestium, which is not found in the manuscript. The editor did not use Copernicus's introduction, which stated his theory as actual proof of a Sun-centered universe. Instead, the editor inserted an unsigned preface written by Osiander, which presented the observations simply as a method for calculating the positions of heavenly bodies. The editor did include Copernicus's dedication of the book to Pope Paul III (1468–1549; reigned 1534–49), which explained his reasons for making his discoveries public (see accompanying box). The printed copy of the final volume of the six-volume work reportedly reached Copernicus only a few hours before his death on May 24, 1543.

"I too began to consider."

Only hours before Nicolaus Copernicus died in 1543, he received a copy of De revolutionibus orbium coelestium, which had just been published at Nuremberg, Germany. In this revolutionary six-volume work, Copernicus proposed his theory of a Sun-centered universe. Copernicus had written an introduction stating the theory as actual proof, but it was not included in the book. Instead, the editor had inserted an unsigned preface, written by Lutheran minister Andreas Osiander, that presented the observations simply as a method for calculating the positions of heavenly bodies. The editor did include Copernicus's dedication of the book to Pope Paul III, in which the astronomer explained his reasons for making his discoveries public. Following is an excerpt from the dedication.

For a long time then, I reflected on this confusion in the astronomical traditions concerning the derivation of the motions of the universe's spheres. I began to be annoyed that the movements of the world machine, created for our sake by the best and most systematic Artisan of all [God], were not understood with greater certainty by the philosophers, who otherwise examined so precisely the most insignificant trifles of this world. For this reason I undertook the task of rereading the works of all the philosophers which I could obtain to learn whether anyone had ever proposed other motions of the universe's spheres than those expounded by the teachers of astronomy in the schools. And in fact I found in Cicero that Hicetas supposed the earth to move. Later I also discovered in Plutarch that certain others were of this opinion… Therefore, having obtained the opportunity from these sources, I too began to consider the mobility of the earth.

Nicholas Copernicus. "Letter to Pope Paul III." Preface to De Revolutionibus, as quoted in Nicholas Copernicus on the Revolutions. Translated and edited by Edward Rosen.

Initiates scientific revolution

The thousand copies of the first edition of De revolutionibus orbium coelestium did not sell out, and the work was reprinted only three times prior to the twentieth century. Scientists point out that Copernicus could have done a better job as an observer. He added only twenty-seven observations, an exceedingly meager amount, to the data he took from Ptolemy and from more recent astronomical tables. The accuracy of predicting celestial phenomena on the basis of his system did not exceed the accuracy achieved by Ptolemy. Nevertheless, Copernicus gave important information about the orbits of the planets, and the strength of his work was its appeal to simplicity. For instance, the rotation of the Earth made unnecessary the daily revolution of thousands of stars. In addition, the orbital motion of the Earth fitted perfectly with its period of 365 days into the sequence set by the periods of other planets.

In the tenth chapter of the first book of De revolutionibus orbium coelestium Copernicus compared the Sun to a lamp that lights up the whole universe: "In the center rests the sun. For who would place this lamp of a very beautiful temple in another or better place than this wherefrom it can illuminate everything at the same time." Seventy years later his heliocentric theory of the universe was proven by Galileo. Copernicus is now considered the father of modern astronomy. His work was the first step in the scientific revolution developed by the German astronomer Johannes Kepler (1571–1630; see entry), Galileo, and other scientists in the seventeenth century.

For More Information

Books

Rosen, Edward, translator and editor. Nicholas Copernicus on the Revolutions. Baltimore, Md.: Johns Hopkins University Press, 1978.

Veglahn, Nancy. Dance of the Planets: The Universe of Nicolaus Copernicus. New York: Coward, McCann & Geohegan, 1979.

Westman, Robert S., ed. The Copernican Achievement. Berkeley: University of California Press, 1975.

Web Site

"Copernicus, Nicolaus." Britannica.com. [Online] Available http://www.britannica.com/search?query=copernicus&ct=&fuzzy=N, April 5, 2002.

Knight, Kevin. "Nicholas Copernicus." Catholic Encyclopedia. [Online] Available http://www.newadvent.org/cathen/04352b.htm, November 8, 2001.

"Nicolaus Copernicus." Conventional Wisdom: Selected Quotations Illustrating the Illusions of Popular History. [Online] Available http://www.ari.net/cw/cw.html#copernicus, April 5, 2002.