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

Nicolaus Copernicus

The Polish astronomer Nicolaus Copernicus (1473-1543) was the founder of the heliocentric ordering of the planets.

Nicolaus Copernicus was born on Feb. 19, 1473, in Torun about 100 miles south of Danzig. He belonged to a family of merchants. His uncle, the bishop and ruler of Ermland, was the person to whom Copernicus owed his education, career, and security.

Copernicus studied at the University of Cracow from 1491 to 1494. While he did not attend any classes in astronomy, it was during his student years there that Copernicus began to collect books on astronomy and mathematics. Some of these contain marginal notes by him dating back to that period, but it remains conjectural whether Copernicus had already made at that time a systematic study of the heliocentric theory.

Copernicus returned to Torun in 1494, and in 1496, through the efforts of his uncle, he became a canon at Frauenburg, remaining in that office for the remainder of his life. Almost immediately Copernicus set out for Bologna to study canon law. In Bologna, Copernicus came under the influence of Domenico Maria de Novara, an astronomer known for his admiration of Pythagorean lore. There Copernicus also recorded some planetary positions, and he did the same in Rome, where he spent the Jubilee Year of 1500.

In 1501 there followed a brief visit at home. His first official act as canon there was to apply for permission to spend 3 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 in 1503 the degree of doctor in canon law. 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 85 poems of Theophylactus Simacotta, the 7th-century Byzantine poet. The work, printed in Cracow in 1509, evidenced Copernicus's humanistic leanings. At this time Copernicus was also mulling over the problems of astronomy, and the heliocentric system in particular. The system is outlined in a short manuscript known as the Commentariolus, or small commentary, which he completed about 1512. Copies of it circulated among his friends eager to know the "Sketch of Hypotheses Made by Nicolaus Copernicus on the Heavenly Motions," as Copernicus referred to his work. In it, right at the outset, there was a list of seven axioms, all of which stated a feature specific to the heliocentric system. The third stated in particular: "All the spheres revolve about the sun as their midpoint, and therefore the sun is the center of the universe." The rest of the work was devoted to the elaboration of the proposition that in the new system only 34 circles were needed to explain the motion of planets.

The Commentariolus produced no reaction, either in print or in letters, but Copernicus's fame began to spread. Two years later he received an invitation to be present as an astronomer at the Lateran Council, which had as one of its aims the reform of the calendar; he did not attend. His secretiveness only seemed to further his reputation. In 1522 the secretary to the King of Poland asked Copernicus to pass an opinion on De motu octavae spherae (On the Motion of the Eighth Sphere), just published by Johann Werner, a mathematician of some repute. This time he granted the request in the form of a letter in which he took a rather low opinion of Werner's work. More important was the concluding remark of the letter, in which Copernicus stated that he intended to set forth elsewhere his own opinion about the motion of the sphere of stars. He referred to the extensive study of which parts and drafts were already very likely extant at that time.

Copernicus could pursue his study only in his spare time. As a canon, he was involved in various affairs, including legal and medical, but especially administrative and financial matters. In fact, he composed a booklet in 1522 on the remedies of inflation, which then largely meant the preservation of the same amount of gold and silver in coins. For all his failure to publish anything in astronomy, to have his manuscript studies circulate, or to communicate with other astronomers, more and more was rumored about his theory, still on the basis of the Commentariolus.

Not all the comments were flattering. Luther denounced Copernicus as "the fool who will turn the whole science of astronomy upside down." In 1531 a satirical play was produced about him in Elbing, Prussia, by a local schoolmaster. In Rome things went better, for the time being at least. In 1533 John Widmanstad, a papal secretary, lectured on Copernicus's theory before Pope Clement VII and several cardinals. Widmanstad's hand was behind the letter which Cardinal Schönberg sent in 1536 from Rome to Copernicus, urging him to publish his thoughts, or at least to share them with him.

It was a futile request. Probably nobody knew exactly how far Copernicus had progressed with his work until Georg Joachim (Rheticus), a young scholar from Wittenberg, arrived in Frauenburg in the spring of 1539. When he returned to Wittenberg, he had already printed an account, known as the Narratio prima, of Copernicus's almost ready book. Rheticus was also instrumental in securing the printing of Copernicus's book in Nuremberg, although the final supervision remained in the care of Andrew Osiander, a Lutheran clergyman. He might have been the one who gave the work its title, De revolutionibus orbium coelestium, which is not found in the manuscript. But Osiander certainly had written the anonymous preface, in which Copernicus's ideas were claimed to be meant by their author as mere hypotheses, or convenient mathematical formalism, that had nothing to do with the physical reality.

The printed copy of his work, in six books, reached Copernicus only a few hours before his death on May 24, 1543. The physics of Copernicus was still Aristotelian and could not, of course, cope with the twofold motion attributed to the earth. But Copernicus could have done a better job as an observer. He added only 27 observations, an exceedingly meager amount, to the data he took over un-critically 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. Nor could Copernicus provide proof for the phases of Mercury and Venus that had to occur if his theory was true. The telescope was still more than half a century away. Again, Copernicus could only say that the stars were immensely far away to explain the absence of stellar parallax due to the orbital motion of the earth. Here, the observational evidence was not forthcoming for another 300 years. Also, while Ptolemy actually used only 40 epicycles, their total number in Copernicus's system was 84, hardly a convincing proof of its greater simplicity.

Still, the undeniable strength of Copernicus's work lay in its appeal to simplicity. The rotation of the earth made unnecessary the daily revolution of thousands of stars. The orbital motion of the earth fitted perfectly with its period of 365 days into the sequence set by the periods of other planets. Most importantly, the heliocentric ordering of planets eliminated the need to think of the retrograde motion of the planets as a physical reality. In the tenth chapter of the first book Copernicus made the straightforward statement: "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."

The thousand copies of the first edition of the book did not sell out, and the work was reprinted only three times prior to the 20th century. No "great book" of Western intellectual history circulated less widely and was read by fewer people than Copernicus's Revolutions. Still, it not only instructed man about the revolution of the planets but also brought about a revolution in human thought by serving as the cornerstone of modern astronomy.

Further Reading

A popular modern account of Copernicus's life is A. Armitage, The World of Copernicus (1947). In Thomas Kuhn, The Copernican Revolution (1957), Copernicus's theory is discussed in the framework of the process leading from ancient to modern science through the medieval and Renaissance centuries. For a rigorous discussion of Copernicus's theory the standard modern work is A. Koyré, The Astronomical Revolution: Copernicus, Kepler, Borelli (1969). □

Nicolaus Copernicus

Born: February 19, 1473
Torun, Poland
Died: May 24, 1543
Frauenberg, East Prussia (now Frombork, Poland)
Polish astronomer

The Polish astronomer Nicolaus Copernicus was the founder of the heliocentric ordering of the planets, which at the time was a revolutionary idea that stated the Earth and other planets revolve around the Sun.

Early life

Nicolaus Copernicus was born on February 19, 1473, in Torun, Poland, about 100 miles south of Danzig. He belonged to a family of merchants. His uncle, the bishop and ruler of Ermland, was the person to whom Copernicus owed his education, career, and security.

Copernicus studied at the University of Cracow from 1491 to 1494. While he did not attend any classes in astronomy, it was during his student years there that Copernicus began to collect books on mathematics and astronomy (the study of the universe). Copernicus returned to Torun in 1494. In 1496, through the efforts of his uncle, he became a canon (priest) at Frauenburg, remaining in that office for the remainder of his life. Copernicus then set out for Bologna, Italy, to study canon law. In Bologna Copernicus came under the influence of Domenico Maria de Novara, an astronomer. There Copernicus also recorded some planetary positions, and he did the same in Rome, where he spent the year of 1500.

Upon returning to Ermland in 1506, Copernicus stayed in his uncle's castle at Heilsberg as his personal physician (doctor) and secretary. During that time he translated from Greek into Latin the eighty-five poems of Theophylactus Simacotta, the seventh-century poet. The work, printed in Cracow in 1509, demonstrated Copernicus's interest in the arts.

The heliocentric system

At this time Copernicus was thinking about problems of astronomy, and the heliocentric system in particular. The system is outlined in a short manuscript known as the Commentariolus, or small commentary, which he completed about 1512. In it there was a list of seven axioms (truths), all of which stated a feature specific to the heliocentric system. The third stated in particular: "All the spheres revolve about the sun as their midpoint, and therefore the sun is the center of the universe."

The Commentariolus produced no reaction, either in print or in letters, but Copernicus's fame began to spread. Two years later he turned down an invitation to be present as an astronomer at the Lateran Council, which had the reform (improvement) of the calendar as one of its aims. His secretiveness only seemed to further his reputation. In 1522 the secretary to the King of Poland asked Copernicus to pass an opinion on De motu octavae spherae (On the Motion of the Eighth Sphere ), just published by Johann Werner, a mathematician. This time he granted the request in the form of a letter in which he took a rather low opinion of Werner's work. More important was the closing of the letter, in which Copernicus stated that he intended to present his own opinion about the motion of the stars.

Copernicus could pursue his study only in his spare time. As a canon he was involved in various affairs, including legal and medical, but especially administrative and financial matters. For all his failure to publish anything in astronomy, his manuscript studies presented in Commentariolus continued to circulate, and more and more was rumored about his theory.

Criticisms

Not all the comments were flattering, though. German religious reformer Martin Luther (1483–1546) said Copernicus was "the fool who will turn the whole science of astronomy upside down." In 1531 a local schoolmaster produced an unflattering play about him in Elbing, Prussia. In Rome things went better, for the time being at least. In 1533 John Widmanstad, a secretary to the pope, lectured on Copernicus's theory before Pope Clement VII (1536–1605) and several cardinals (religious leaders ranking just below the pope). Widmanstad's hand was behind the letter that Cardinal Schönberg sent from Rome to Copernicus in 1536 urging him to publish his thoughts, or to share them with him at least.

In 1539 Georg Joachim (Rheticus), a young scholar from Wittenberg, arrived in Frauenburg and printed an account, known as the Narratio prima, of Copernicus's book, which was nearing completion. Rheticus was also instrumental in securing the printing of Copernicus's book in Nuremberg, Germany, although the final supervision remained in the care of Andrew Osiander, a Lutheran clergyman (religious leader). He might have been the one who gave the work its title, De revolutionibus orbium coelestium, which is not found in the manuscript. But Osiander certainly had written the anonymous preface (the introduction to the book written by an unknown author), in which Copernicus's ideas were claimed to be meant by their author as mere hypotheses (theories) that had nothing to do with the physical reality.

Copernicus received the printed copy of his work in six books, only a few hours before his death on May 24, 1543. Although there were many gaps in Copernicus's theories, he could have done a better job as an observer. He added only twenty-seven observations to the data he took over from Ptolemy (c. 100–c. 165 C. E.), a second century astronomer, and from more recent astronomical tables. The invention of the telescope was still more than half a century away. To explain the absence of stellar parallax (a change in the direction) due to the orbital motion of the earth, Copernicus could only say that the stars were immensely far away. Here, the observational evidence would not come for another three hundred years. Also, while Ptolemy actually used only forty epicycles (describes the orbit of planets), their total number in Copernicus's system was eighty-four, hardly a convincing proof of its greater simplicity.

Still, the undeniable strength of Copernicus's work lay in its appeal to simplicity. The rotation of the earth made the daily revolution of thousands of stars unnecessary. The orbital motion of the earth fit perfectly into the sequence set by the periods of other planets with its period of 365 days. Most importantly, the heliocentric ordering of planets eliminated the need to think of the retrograde motion (direction opposite of the earth's motion) of the planets as a physical reality. In the tenth chapter of the first book Copernicus made the straightforward statement: "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."

The thousand copies of the first edition of the book did not sell out, and the work was reprinted only three times prior to the twentieth century. No "great book" of Western intellectual history circulated less widely and was read by fewer people than Copernicus's Revolutions. Still, it not only instructed man about the revolution of the planets but also brought about a revolution in human thought by serving as the building block of modern astronomy.

For More Information

Andronik, Catherine M. Copernicus: Founder of Modern Astronomy. Berkeley Heights, NJ: Enslow, 2002.

Hallyn, Fernand. The Poetic Structure of the World: Copernicus and Kepler. New York: Zone Books, 1990.

Koyré, A. The Astronomical Revolution: Copernicus, Kepler, Borelli. Ithaca, NY: Cornell University Press, 1973.

Nicolaus Copernicus (1473-1543)

Polish astronomer and mathematician

Source

Education. Nicolaus Copernicus was born in Poland in 1473. As a young man he excelled in his studies at the University of Cracow, developing in the process a particular fascination with the subjects of astronomy and mathematics. Abandoning his native Poland in 1496, Copernicus traveled to Italy to continue his education. A decade of study at some of Italy’s leading universities exposed him to the scientific thought of the ancient Greeks and Romans. A somewhat shy and conservative man, Copernicus at this stage of his life certainly did not appear to be the sort of intellectual whose work would eventually revolutionize astronomy and call into question traditional European conceptions of humankind’s place in the universe. After returning from Italy to his Polish homeland, in fact, Copernicus became a Catholic clergyman and led a relatively obscure life at the cathedral in Frauenberg. During his years at Frauenberg, however, Copernicus gradually developed a new system of astronomical thought that proved to be, quite literally, earthmoving.

Aristotle and Ptolemy. In Copernicus’s time Europe’s view of the universe continued to be based upon the ideas of the Greek philosopher Aristotle. According to Aristotle the earth upon which we live is a stable, motionless sphere located at the very center of the universe. At the outer edge of Aristotle’s universe stood a much larger “sphere of fixed stars,” a hollow, rotating glass ball into which were embedded the stars that we see circling across the nighttime sky. In the space between the central earth and the outer sphere of fixed stars were several “planets” that orbited circularly around the earth. According to Aristotle’s scheme the sun was one of these planets that circled the earth each day. In the second century a.d. the geographer and astronomer Ptolemy wrote a highly influential book, the Almagest, summarizing Aristotelian astronomical thought and providing observational and mathematical data regarding the motions of the sun and the other planets. Aristotle’s conceptual scheme of the universe, combined with the mathematical details provided by Ptolemy, dominated European astronomical thought well into the 1500s.

The Moving Earth. Copernicus was hardly the first scholar to notice that Ptolemy’s mathematical descriptions of planetary motion did not match exactly with the actual observed paths of the sun and planets through the sky. Many astronomers throughout the Middle Ages, in fact, proposed minor adjustments to Ptolemy’s system but always maintained the basic Aristotelian assumptions that the earth lay motionless at the center of the universe and that the sun revolved around the earth. In the early decades of the sixteenth century, however, the quiet and studious Polish clergyman Copernicus arrived at the radical conclusion that astronomy could more accurately account for the motion of the planets if it abandoned the old idea that the earth was located at the center of the universe. Copernicus instead suggested that it was the sun that occupied the central position and that the earth was simply one of the many planets that revolved around the sun.

The Theory. Copernicus’s ideas threatened not only traditional astronomical thought but also other long-held scientific and religious principles. First, the old earth-centered conception of the universe had long appealed to Christian thinkers since it placed humankind at the center of God’s creation. As a Catholic clergyman Copernicus understood that his new system, by placing the sun rather than the earth at the center, removed humankind from its special position in God’s universe. Second, the stable, motionless earth of the old Aristotelian model had been a key element of medieval physics. If the earth was constantly and rapidly hurtling through the heavens, Copernicus’s Aristotelian critics would ask, then why do objects on the earth’s surface not go flying off? Fully aware of the controversy that his sun-centered model would cause, the naturally timid Copernicus kept his radical ideas to himself for most of his life. Only in 1543, the year of his death, was his theory finally published in a book titled On the Revolution of the Heavenly Spheres. The publication of Copernicus’s theory did not, however, cause an immediate revolution in European astronomical thought. The old Aristotelian system continued to prove convincing to most European intellectuals through the end of the 1500s in part because of religious considerations and in part because it seemed to provide a better common-sense explanation of observed physical reality than did the Copernican model. Only in the 1600s and 1700s, following the work of such noted scientists as Galileo Galilei and Isaac Newton, was Copernicus’s idea of a moving earth incorporated into a new and widely accepted modern worldview.

Age of Exploration. Copernicus’s revolutionary astronomical ideas were emblematic of the sorts of radical transformations that characterized European intellectual life in the age of exploration and expansion. However, even though European exploration shared with the Copernican revolution common roots in the inquisitive spirit of the Renaissance era, the two movements were in many ways opposed to one another. In fact European navigators in the age of exploration and expansion had particularly strong reasons to reject Copernicus’s idea of a moving earth. By the time of Copernicus, European sailors had become highly adept at navigating by the stars on the open sea. Such navigational techniques were based, in fact, on the Aristotelian model of the universe. From their supposedly stationary earth at the center of the universe, navigators measured the position of heavenly bodies on the universe’s outer sphere of fixed stars in order to calculate their position on the earth. If the earth were constantly moving as Copernicus suggested, then their navigational calculations would be thrown way off the mark. To European sailors, in other words, common sense and practical experience remained thoroughly Aristotelian. The achievements of European navigation in the age of exploration and expansion illustrate, in fact, the powerful explanatory power of the Aristotelian model of the universe and help to explain why Europeans took so long to abandon it. As a scientific model of the actual universe, the old Aristotelian system has in fact been thoroughly discredited by the achievements of modern science. As a practical basis for navigation, however, the Aristotelian model proved highly effective and useful.

Source

Thomas Kuhn, The Copernican Revolution: Planetary Astronomy in the Development of Western Thought (Cambridge, Mass.: Harvard University Press, 1957).

Copernicus, Nicolas (1473-1543)

Polish astronomer and mathematician

Nicolas Copernicus was born into a well-to-do family on February 19, 1473. His father, a copper merchant, died when Copernicus was 10, and the boy was taken in by an uncle who was a prince and bishop.

Copernicus was able to afford an excellent education. He entered the University of Cracow in 1491 and studied mathematics and painting. In 1496, he went to Italy for 10 years where he studied medicine and religious law. Two things happened in the year 1500 that influenced Copernicus; he attended a conference in Rome dealing with calendar reform and, on November 6, 1500, he witnessed a lunar eclipse .

The tables of planetary positions that were in use at the time were complex and inaccurate. Predicting the positions of the planets over long periods of time was haphazard at best, and the seasons were out of step with the position of the Sun . Copernicus realized that tables of planetary positions could be calculated much more easily, and accurately, if he made the assumption that the Sun, not Earth, was the center of the solar system and that the planets, including Earth, orbited the Sun. He first proposed this theory in 1507.

Copernicus was not the first person to introduce such a radical concept. Aristarchus had come up with the idea in ancient Greece long before, but the teachings of Ptolemy had been dominant for 1,300 years. Ptolemy claimed the earth was at the center of the universe, and all the planets (including the Sun and Moon ) were attached to invisible celestial spheres that rotated around the earth.

Copernicus not only wished to refute Ptolemy's universe, he claimed that Earth itself was very small and unimportant compared to the vast vault of the stars. This marked the beginning of the end of the influence of the ancient Greek scientists.

Copernicus made an incorrect assumption about planetary orbits; he decided they were perfectly circular. Because of this, he found it necessary to use some of Ptolemy's cumbersome epicycles (smaller orbits centered on the larger ones) to reduce the discrepancy between his predicted orbits and those observed. It wasn't until Johannes Kepler's time that this was corrected and the true nature of planetary orbits was understood.

Even so, the heliocentric model developed by Copernicus fit the observed data better than the ancient Greek concept. For example, the periodic "backward" motion in the sky of the planets Mars, Jupiter, and Saturn and the lack of such motion for Mercury and Venus was more readily explained by the fact that the former planets' orbits were outside of Earth's. Thus, the earth "overtook" them as it circled

the Sun. Planetary positions could also be predicted much more accurately using Copernicus' model.

Copernicus was reluctant to make his ideas public. He realized his theory not only contradicted the Greek scientists, it went against the teachings of the Church, the consequences of which could be severe. In 1530, he allowed a summary of his ideas to circulate among scholars, who received it with great enthusiasm, but it was not until just shortly before his death in 1543 that his entire book was published. It took the efforts of the mathematician Rheticus to convince Copernicus to grant him permission to print it. Unfortunately, Rheticus had fallen afoul of official doctrine himself, and found it wise to leave town. Overseeing the publication for Copernicus's book was transferred to the hands of a Lutheran minister named Andreas Osiander (1498–1552).

Osiander now found he was in a tight spot; Martin Luther (1483–1546) had come out firmly against Copernicus' new theory, and Osiander was obligated to follow him. "This Fool wants to turn the whole Art of Astronomy upside down," Luther had said. Copernicus had dedicated his book to Pope Paul III, perhaps to gain favor, but Osiander went one step further; he wrote a preface in which he stated the heliocentric theory was not being presented as actual fact, but just as a concept to allow for better calculations of planetary positions. He did not sign his name to the preface, making it appear that Copernicus had written it and was debunking his own theory. Copernicus, suffering from a stroke and close to death, could do nothing to defend himself. It is said he died only hours after seeing the first copy of the book. Kepler discovered the truth about the preface in 1609 and exonerated Copernicus.

The immediate reaction to the book, De Revolutionibus Orbium Coelestium (Revolution of the heavenly spheres), was subdued. This was primarily due to Osiander's preface, which weakened Copernicus' reputation. In addition, only a limited number of books were printed, they were very expensive and, consequently, had limited circulation. The book did achieve a number of converts, but one had to be a mathematician to fully understand the theories. Still, it was placed on the Roman Catholic Church's list of prohibited books where it remained until 1835.

Almost as significant as proving the heliocentric solar system was possible, was Copernicus's questioning of the ancient Greek scientists. Ptolemy had bent the facts to fit his preconceived theory and his teachings had been accepted, without question, for centuries. Copernicus, on the other hand, did his best to develop his theory to match observed facts, foreshadowing the dawning of modern scientific method .

Copernicus, Nicolaus (1473–1543)

Polish astronomer who proposed a heliocentric (sun-centered) universe, an important foundation of modern scientific thought. Born in the town of Thorn (or Torun), then ruled by Poland, Copernicus was a member of a well-to-do merchant family. After the death of his father, he

joined the household of his uncle, a local bishop, who saw to Nicolaus's upbringing and education. Nicolaus attended the university in Krakow, Poland, and then studied at Bologna and Padua in Italy, taking up law and mathematics. At the insistence of his uncle, he also became a trained physician. His true interest, however, lay in astronomy. While a student in Ferrara, Italy, he attended lectures given by the astronomer Domenico Maria Novara de Ferrara, who accepted Copernicus for a time as his assistant. Copernicus also traveled to Rome, where he held lectures on astronomy and made observations of a lunar eclipse.

When he returned to Poland, Copernicus was appointed as a canon of the cathedral at Frauenberg, where he earned a steady income as a church administrator. From his house, he observed the stars and planets and worked out a theory contrary to the notion of the ancient Greeks. Aristotle and Ptolemy believed the earth was the center of the universe; Ptolemy proposed the idea that the stars and planets move about the earth in a series of concentric shells. The Ptolemaic system became the accepted dogma of the Catholic Church, which during the Renaissance was still condemning new scientific ideas as impious heresies.

In the Copernican system, the universe is heliocentric, with the earth, stars, moon, and planets all revolving around the sun. The Copernican system explained the mysterious retrograde motion of the planets, which occasionally seem to move backward in their nightly tracks through the sky. Astronomers of ancient and medieval times had to explain retrograde motion with a series of complex schemes and mathematical calculations, while the heliocentric system solved it by pointing out that the position of planets in different orbits about the sun can have irregular positions to an observer on earth.

Copernicus summarized these ideas in a treatise, Brief Commentary, that he passed among friends and colleagues starting in about 1512. He kept a more detailed work that he entitled On the Revolutions, in manuscript form. In the meantime, he served in his professional capacities as a church canon, a doctor, and a tax collector. He produced a useful essay on the problem of monetary inflation in which he astutely observed that money will lose its value as more of it circulates. Copernicus's opinions and remedies on this subject, although effective, have been completely overlooked by his astronomy.

Copernicus's ideas were spreading throughout Europe despite his desire to keep them secret. He feared the harsh opinions of scientists, who were sure to ridicule his notion, as well as the judgment of the church, which he believed might find him to be a heretic. He was roundly criticized by the Protestant reformers at the same time Pope Clement VII and his cardinals were learning of the heliocentric theory through reports and lectures in Rome. In 1539 George Rheticus, a scholar attending the University of Wittenberg, met Copernicus, who agreed to tutor the younger man in mathematics and astronomy. Rheticus enthusiastically accepted the heliocentric theory and wrote his own treatise detailing it, entitled First Account. This emboldened Copernicus to bring out his own book, On the Revolutions, which was finally published in 1543, just a few weeks before its author died.

The Copernican system began a scientific and philosophical revolution in Europe. By moving the earth from its symbolic position at the center of the universe, it forced astronomers to consider the possibility that the known world was but a small and insignificant part of all creation. It also suggested that human observation and perception often led to false or misleading conclusions about the true state of the natural world. Scientific skepticism began with this questioning of a phenomenon obvious to everyone: that the sun moves through the sky every day.

The heliocentric theory was gradually accepted and modified by the leading astronomers and scientists in Europe, including Johannes Kepler and Galileo Galilei (who was among the first to make astronomical observations with a telescope). The Catholic Church, however, found the Copernican system to be contrary to accepted Christian doctrine, and placed On the Revolutions on its Index of prohibited books in 1616. The Enlightenment, a movement of natural philosophy that rejected religious doctrine as a basis for scientific observation altogether, accepted the heliocentric system in the eighteenth century. But it wasn't until 1835 that the book of Copernicus detailing this system was taken off the list of books banned by the Vatican.

See Also: astronomy; Brahe, Tycho; Galilei, Galileo; Kepler, Johannes

Copernicus, Nicholas

Polish Astronomer 1473-1543

Nicholas Copernicus was a Polish astronomer who changed humankind's view of the universe. Greek astronomers, particularly Ptolemy, had argued that Earth was the center of the universe with the Sun, Moon, planets, and stars orbiting around it. This geocentric (Earth-centered) model, however, could not easily explain retrograde motion, the apparent backwards movement that planets exhibit at some points in their paths across the sky. Ptolemy and others had proposed a complicated system of superimposed circles to explain retrograde motion under the geocentric model. Copernicus realized that if all the planets, including Earth, orbited the Sun, then retrograde motion resulted from the changing of perspective as Earth and the other planets moved in their orbits.

Copernicus published his heliocentric (Sun-centered) theory in the book De revolutionibus orbium coelesticum (On the revolutions of the celestial orbs). The Catholic Church, however, had accepted the geocentric model as an accurate description of the universe, and anyone arguing against this model faced severe repercussions. At the time, Copernicus was gravely ill, so he asked Andreas Osiander to oversee the book's publication. Osiander, concerned about the Church's reaction, wrote an unsigned preface to the book stating that the model was simply a mathematical tool, not a true depiction of the universe. Copernicus received the first copy of his book on his deathbed and never read the preface. The telescopic discoveries of Italian mathematician and astronomer Galileo Galilei (1564-1642) and the mathematical description of planetary orbits by German astronomer Johannes Kepler (1571-1630) led to the acceptance of Copernicus's heliocentric model.

see also Astronomy, History of (volume 2); Galilei, Galileo (volume 2); Kepler, Johannes (volume 2).

Nadine G. Barlow

Bibliography

Andronik, Catherine M. Copernicus: Founder of Modern Astronomy. Berkeley Heights, NJ: Enslow Publishers, 2002.

Gingerich, Owen. The Eye of Heaven: Ptolemy, Copernicus, Kepler. New York: American Institute of Physics, 1993.

Nicholas Copernicus , Pol. Mikotaj Kopérnik, 1473–1543, Polish astronomer. After studying astronomy at the Univ. of Kraków, he spent a number of years in Italy studying various subjects, including medicine and canon law. He lectured c.1500 in Rome on mathematics and astronomy; in 1512 he settled in Frauenburg, East Prussia, where he had been nominated canon of the cathedral. There he performed his canonical duties, practiced medicine, was a legal officer, and wrote a pioneering treatise on currency reform. But the work that immortalized him is De revolutionibus orbium coelestium, in which he set forth his beliefs concerning the universe, known as the Copernican system . That treatise, which was dedicated to Pope Paul III, was probably completed by 1530 but was not published until 1543, when Copernicus was on his deathbed. Modern astronomy was built upon the foundation of the Copernican system.

Bibliography: See his complete works (3 vol., 1973–85, ed. and tr. by E. Rosen); biography by J. Repcheck (2007); studies by E. Rosen (1984, 1995) and O. Gingerich (2004).

Copernicus, Nicolaus (1473–1543)Polish churchman and astronomer of German parentage (in Polish, Mikołaj Kopernigk). While a student he had come to believe that the Earth revolves around the Sun and not vice versa. Such a view was held to be heretical, the Church regarding the geocentric world-view of Aristotle and Ptolemy as consistent with its doctrines. Copernicus set down his basic ideas around 1510 in the Commentariolus, which was circulated anonymously. In 1512–29 he made the observations that he needed to support his theory, while carrying out ecclesiastic and local administrative duties. In 1539 the Austrian astronomer and mathematician Georg Joachim von Lauchen (1514–74), known as Rheticus, became a pupil of Copernicus and began to spread his ideas. The Copernican system was published openly in 1543 in the book De revolutionibus orbium coelestium. However, the reality of a heliocentric Solar System came to be accepted only after the work of Galileo and J.Kepler.

Copernicus, Nicolas (1473–1543) ( Mikolaj Kopernik) Polish astronomer. Through his study of planetary motions, Copernicus developed a heliocentric (Sun-centred) theory of the universe in opposition to the accepted geocentric (Earth-centred) theory conceived by Ptolemy nearly 1500 years before. In the Copernican system (as it is now called) the planets' motions in the sky were explained by their orbit of the Sun. The motion of the sky was simply a result of the Earth turning on its axis. An account of his work, De revolutionibus orbium coelestium, was published in 1543. Most astronomers considered the new system as merely a means of calculating planetary positions, and continued to believe in Aristotle's view of the world. See also Galileo; Kepler

Copernicus, Nicholas (1473–1543), astronomer. From 1495 he held a canonry in Frauenburg (NE Poland) and lived there from 1510. By 1514 he had written a short treatise, the Commentariolus (first published in 1878), sketching out a new system of astronomy in which the sun rather than the earth was the centre of the universe, and the earth one of the planets revolving round it. This was given mature expression in his De revolutionibus orbium caelestium (1543). Theological objections were muted at first, but when the issues were popularized by G. Galileo, religious debate became intense and in 1616 the De revolutionibus was put on the Index.

Copernicus, Latinized form of the surname of Nicolas Koppernik (1473–1543), astronomer, native of Torun, Poland, who propounded in his De Revolutionibus (1543) the theory that the planets, including the earth, move in orbits round the sun as centre, in opposition to Ptolemy's earlier geocentric theory.

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