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Nicolaus Copernicus (in Latin; Polish: Mikołaj Kopernik; German: Nikolaus Kopernikus; February 19, 1473 – May 24, 1543) was a Polish astronomer, mathematician and economist who developed the heliocentric (Sun-centered) theory of the solar system in a form detailed enough to make it scientifically useful. His main occupations and services rendered were in Royal Prussia, as church canon, governor and administrator, economist, jurist, physician, astrologer and military leader (conducting defense against the Teutonic Order). Amid all his responsibilities, he treated astronomy as one would a hobby. His theory about the Sun as the center of the Universe, opposed to the traditional geocentric theory that placed Earth at the center, is considered one of the most important discoveries ever, and is the fundamental starting point of modern astronomy and modern science itself (it inaugurated a scientific revolution). His theory affected many aspects of human life, opening the door for young astronomers, scientists and scholars to take a skeptical attitude toward established dogma.

BIOGRAPHY

Copernicus was born in 1473 at Toruń (Thorn) in Polish Royal Prussia. His father Nikolas, a citizen of Kraków (Cracow), then capital of Poland, had moved to Toruń in 1460 once the war with the Teutonic Knights was concluded, and had become a respected citizen of that city. Copernicus was ten when his father, a wealthy businessman and copper trader, died. Little is known of his mother, Barbara Watzenrode, who appears to have predeceased her husband. Copernicus' maternal uncle, Lucas Watzenrode, a church canon and later Prince-Bishop governor of Warmia, reared him and his three siblings after the death of Copernicus' father. Copernicus' brother Andreas became a canon at Frombork (Frauenburg). A sister, Barbara, became a Benedictine nun, and the other sister, Katharina, married a businessman and city councillor, Barthel Gertner. In 1491 Copernicus enrolled at the Jagiellonian University in Kraków, and here for the first time encountered astronomy, thanks to his teacher Albert Brudzewski. This science soon fascinated him, as shown by his books (later carried off as war booty by the Swedes during The Deluge, and now at the Uppsala University Library). After four years at Kraków, followed by a brief stay at Toruń, he went to Italy, where he studied law and medicine at the universities of Bologna and Padua. His bishop-uncle financed his education and wished for him to become a bishop as well. However, while studying canon and civil law at Ferrara, Copernicus met the famous astronomer, Domenico Maria Novara da Ferrara. Copernicus attended his lectures and became his disciple and assistant. The first observations that Copernicus made in 1497, together with Novara, are recorded in Copernicus' epochal book, De revolutionibus orbium coelestium.

In 1497 Copernicus' uncle was ordained Bishop of Warmia, and Copernicus was named a canon at Frombork (Frauenburg) Cathedral, but he waited in Italy for the great Jubilee of 1500. Copernicus went to Rome, where he observed a lunar eclipse and gave some lectures in astronomy or mathematics.

He would thus have visited Frombork only in 1501. As soon as he arrived, he requested and obtained permission to return to Italy to complete his studies at Padua (with Guarico and Fracastoro) and at Ferrara (with Bianchini), where in 1503 he received his doctorate in canon law. It has been supposed that it was in Padua that he encountered passages from Cicero and Plato about opinions of the ancients on the movement of the Earth, and formed the first intuition of his own future theory. His collection of observations and ideas pertinent to his theory began in 1504.

Having left Italy at the end of his studies, he came to live and work at Frombork. Some time before his return to Warmia, he had received a position at the Collegiate Church of the Holy Cross in Wrocław (Breslau), Silesia, which he would resign a few years before his death. Through the rest of his life he made astronomical observations and calculations, but always in his spare time and never as a profession.

Copernicus worked for years with the Prussian diet on monetary reform and published some studies about the value of money; as governor of Warmia, he administered taxes and dealt out justice. It was at this time (beginning in 1519, the year of Thomas Gresham's birth) that Copernicus came up with one of the earliest iterations of the theory now known as Gresham's Law. During these years he also traveled extensively on government business and as a diplomat, on behalf of the Prince-Bishop of Warmia.

In 1514 he made his Commentariolus — a short handwritten text describing his ideas about the heliocentric hypothesis — available to friends. Thereafter he continued gathering evidence for a more detailed work.

During the war between the Teutonic Order and the Kingdom of Poland (1519–1524) Copernicus successfully defended Allenstein (Olsztyn) at the head of royal troops besieged by the forces of Albert of Brandenburg.

In 1533 Albert Widmanstadt delivered a series of lectures in Rome outlining Copernicus' theory. By 1536 Copernicus' work was already in definitive form, and some rumors about his theory had reached scientists all over Europe. From many parts of the continent, Copernicus received invitations to publish, but he feared persecution for his revolutionary work by the establishment. Cardinal Nicola Schoenberg of Capua wrote, asking him to communicate his ideas more widely and requesting a copy for himself; "Therefore, learned man, without wishing to be inopportune, I beg you most emphatically to communicate your discovery to the learned world, and to send me as soon as possible your theories about the Universe, together with the tables and whatever else you have pertaining to the subject." Some have suggested that this note may have made Copernicus leery of publication, while others have suggested that the Church wanted to ensure that his ideas were published.

Copernicus was still completing his work (even if he was not convinced that he wanted to publish it) when in 1539 Georg Joachim Rheticus, a great mathematician from Wittenberg, arrived in Frombork. Philipp Melanchthon had arranged for Rheticus to visit several astronomers and study with them. Rheticus became a disciple of Copernicus' and stayed with him for two years, during which he wrote a book, Narratio prima, outlining the essence of the theory.

In 1542, in Copernicus' name, Rheticus published a treatise on trigonometry (later included in the second book of De revolutionibus). Under strong pressure from Rheticus, and having seen that the first general reception of his work had not been unfavorable, Copernicus finally agreed to give the book to his close friend Tiedemann Giese, bishop of Chełmno (Kulm), to be delivered to Rheticus for printing at Nuremberg.

Legend says that the first printed copy of De revolutionibus was placed in Copernicus' hands on the day he died, so that he could take farewell of his opus vitae. He supposedly woke from a stroke-induced coma, looked at his book, and died peacefully.

Copernicus was buried in Frombork Cathedral. Archeologists searching for his remains had failed to locate them, though they had found interesting graves from various periods. On November 3, 2005, archeologists announced that in August they had recovered Copernicus' skull.

The Copernican heliocentric system
Earlier theories

Much has been written about earlier heliocentric theories. Philolaus (4th century BC) was one of the first to hypothesize movement by the Earth, probably inspired by Pythagoras' theories about a spherical Globe.

Aristarchus of Samos in the 3rd century BC had developed some theories of Heraclides Ponticus (speaking of a revolution by Earth on its axis) to propose what was, so far as is known, the first serious model of a heliocentric solar system. His work about a heliocentric system has not survived, so one may only speculate about what led him to his conclusions. It is notable that, according to Plutarch, a contemporary of Aristarchus accused him of impiety for "putting the Earth in motion."

Indian mathematicians, astronomers and physicians, most notably Aryabhata and Bhaskara I, also anticipated Copernicus' discoveries, by about 1,000 years. The work of the 14th-century Muslim astronomer Ibn al-Shatir contains findings similar to Copernicus', and it has been suggested that Copernicus might have been influenced by them.

Copernicus cited Aristarchus and Philolaus in an early manuscript of his book which survives, stating: "Philolaus believed in the mobility of the earth, and some even say that Aristarchus of Samos was of that opinion." For reasons unknown, he struck this passage before publication of his book.

Inspiration came to Copernicus not from observation of the planets, but from reading two authors. In Cicero he found an account of the theory of Hicetas. Plutarch provided an account of the Pythagoreans Heraclides Ponticus, Philolaus, and Ecphantes. These authors had proposed a moving earth that revolved around a central sun. Copernicus did not attribute his inspiration to Aristarchus as is sometimes stated. When Copernicus' book was published, it contained a preface by the Lutheran theologian Andreas Osiander. This cleric stated that Copernicus wrote his heliocentric account of the earth's movement as a mere mathematical hypothesis, not as an account that contained truth or even probability. Copernicus' hypothesis contradicted the account of the sun's movement around the earth that appears in the Old Testament (Joshua 10:13).

The Ptolemaic system

The prevailing theory in Europe as Copernicus was writing was that created by Ptolemy in his Almagest, dating from about 150 A.D.. The Ptolemaic system drew on many previous theories that viewed Earth as a stationary center of the universe. Stars were embedded in a large outer sphere which rotated relatively rapidly, while the planets dwelt in smaller spheres between — a separate one for each planet. To account for apparent anomalies to this view, such as the retrograde motion observed in many planets, a system of epicycles was used, by which a planet rotated on a small axis while also rotating on a larger axis around the Earth. Some planets were assigned "major" epicycles (by which retrograde motion could be observed) and "minor" epicycles (which simply warped the overall rotation).

A complementary theory to Ptolemy's employed homocentric spheres: the spheres within which the planets rotated, could themselves rotate somewhat. Also popular with astronomers were variations such as eccentrics — by which the rotational axis was offset and not completely at the center — or that added epicycles to epicycles.

Ptolemy's unique contribution to this theory was the idea of an equant — a complicated addition which specified that, when measuring the rotation of the Sun, one sometimes used the central axis of the universe, but sometimes one set at a different location. This had an overall effect of making certain orbits "wobble," a fact that would greatly bother Copernicus (such wobbling rendered implausible the idea of material "spheres" in which the planets rotated). In the end, after all these complications, the astronomers could still not get observation and theory to match up exactly. In Copernicus' day, the most up-to-date version of the Ptolomaic system was that of Peurbach (1423-1461) and Regiomontanus (1436-1476).

Copernican theory

Copernicus' major theory was published in the book, De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres) in the year of his death, 1543, though he had arrived at his theory several decades earlier.

The book marks the beginning of the shift away from a geocentric (and anthropocentric) universe with the Earth at its center. Copernicus held that the Earth is another planet revolving around the fixed sun once a year, and turning on its axis once a day. He arrived at the correct order of the known planets and explained the precession of the equinoxes correctly by a slow change in the position of the Earth's rotational axis. He also gave a clear account of the cause of the seasons: that the Earth's axis is not perpendicular to the plane of its orbit. He added another motion to the Earth, by which the axis is kept pointed throughout the year at the same place in the heavens; since Galileo Galilei, it has been recognized that for the Earth not to point to the same place would have been a motion.

Copernicus also replaced Ptolemy's equant circles with more epicycles. This is the main source of the statement that Copernicus' system had even more epicycles than Ptolemy's. With this change, Copernicus' system showed only uniform circular motions, correcting what he saw as the chief inelegance in Ptolemy's system. But while Copernicus put the Sun at the center of the celestial spheres, he did not put it at the exact center of the universe, but near it.

Copernicus' system was not experimentally better than Ptolemy's model. Copernicus was aware of this and could not present any observational "proof" in his manuscript, relying instead on arguments about what would be a more complete and elegant system. From publication until about 1700, few astronomers were convinced by the Copernican system, though the book was relatively widely circulated (around 500 copies are known to still exist, which is a large number by the scientific standards of the time). Many astronomers, however, accepted some aspects of the theory at the expense of others, and his model did have a large influence on later scientists such as Galileo and Johannes Kepler, who adopted, championed and (especially in Kepler's case) sought to improve it. Galileo's observation of the phases of Venus produced the first observational evidence for Copernicus' theory.

The Copernican system can be summarized in seven propositions, as Copernicus himself collected them in a Compendium of De revolutionibus that was found and published in 1878:

1. Orbits and celestial spheres do not have a unique, common, center.
2. The center of the Earth is not the center of the Universe, but only the center of the Earth's mass and of the lunar orbit.
3. All the planets move along orbits whose center is the Sun, therefore the Sun is the center of the World. (Copernicus was never certain whether the Sun moved or not, claiming that the center of the World is "in the Sun, or near it.")
4. The distance between the Earth and the Sun, compared with the distance between the Earth and the fixed stars, is very small.
5. The daytime motion of the Sun is only apparent, and represents the effect of a rotation that the Earth makes every 24 hours around its axis, always parallel to itself.
6. The Earth (together with its Moon, and just like the other planets) moves around the Sun, so the motions that the Sun seems to be making (its apparent motion during the daytime, and its annual motion through the Zodiac) are nothing else than effects of the Earth's actual motions.
7. These motions of the Earth and of the other planets around the Sun, can explain the stations, and all the particular characteristics of the planets' motions.

Whether these propositions were "revolutionary" or "conservative" was a topic of debate in the late twentieth century. Thomas Kuhn argued that Copernicus only transferred "some properties to the sun many astronomical functions previously attributed to the earth." Other historians have since argued that Kuhn underestimated what was "revolutionary" about Copernicus' work, and emphasized the difficulty Copernicus would have had in putting forward a new astronomical theory relying alone on simplicity in geometry, given that he had no experimental evidence.
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De revolutionibus orbium coelestium

Copernicus' major work, On the Revolutions of the Heavenly Spheres (1543), was the result of decades of labor. It opened with an originally anonymous preface by Andreas Osiander, a theologian friend of Copernicus, who urged that the theory did not necessarily have implications outside the limited realm of astronomy. Copernicus' actual book began with a letter from his (by then deceased) friend, the Archbishop of Capua, urging Copernicus to publish his theory. Then, in a lengthy introduction, Copernicus dedicated the book to Pope Paul III, explaining his ostensible motive in writing the book as relating to the inability of earlier astronomers to agree on an adequate theory of the planets, and noting that if his system increased the accuracy of astronomical predictions it would allow the Church to develop a more accurate calendar (calendar reform then being an important question and one of the major reasons for Church funding of astronomy).

The work itself was then divided into six books.

The first book comprises a general vision of the heliocentric theory, and a summarized exposition of his idea of the World.

The second book is mainly theoretical and presents the principles of spherical astronomy and a list of stars (as a basis for the arguments developed in the subsequent books).

The third book is mainly dedicated to the apparent motions of the Sun and to related phenomena.

The fourth book gives a similar description of the Moon and its orbital motions.

The fifth and sixth books comprise a concrete exposition of the new system.