Nicolaus Copernicus

Nicolaus Copernicus (in Latin; Polish Miko?aj 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, jurist, astrologer and as a doctor. Astronomy was actually a byproduct, a hobby of his. 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 the scientific revolution). His theory affected many other aspects of human life as well, opening the door to young astronomers everywhere to challenge the dogmas and never take anything at face value.

The Copernican heliocentric system

Earlier theories

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

Related Topics:
Philolaus - 4th century BC - Pythagoras

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Aristarchus of Samos (3rd century BC) developed some theories by Heraclides Ponticus (already talking about a revolution of our planet on its axis) to propose what is, to the best of our knowledge, the first serious model of a heliocentric solar system. Unfortunately, his work about his heliocentric hypothesis did not survive, so we can 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".

Related Topics:
Aristarchus - Samos - 3rd century BC - Heraclides Ponticus

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Indian mathematicians, astronomers and physicians, most notably Aryabhata and Bhaskara I, also predate Copernicus' discoveries, by about 1000 years. The work of the 14th century Muslim astronomer Ibn al-Shatir contains results similar to those of Copernicus, and it has even been suggested that Copernicus might have been influenced by them.

Related Topics:
Aryabhata - Bhaskara I - 14th century - Ibn al-Shatir

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Copernicus cited Aristarchus and Philolaus in an early manuscript of his book which has survived, 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 crossed out this passage before publication of his book.

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The Ptolemaic system

The most dominant theory in Europe at the time of Copernicus' writing was that created by Ptolemy in his Almagest, dating from around AD 150. The Ptolemaic system drew on many previous theories before it, viewing Earth as a stationary center of the universe. Stars were embedded in a large external sphere which rotated relatively rapidly, while the planets existed in smaller spheres — a separate sphere for each planet — in between. To account for apparent anomalies to this view, such as the retrograde motion observed in many planets, a system of epicycles where used, by which a planet would rotate on a small axis while also rotating on its larger axis around the Earth. Some planets were assigned "major" epicycles (by which retrograde motion could be observed) and "minor" epicycles (which would simply warp the overall rotation).

Related Topics:
Ptolemy - Almagest - AD 150 - Retrograde - Epicycles

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A complimentary theory to Ptolemy's was one which utilized homocentric spheres — that is, the spheres themselves in which the planets rotated could be somewhat rotated. Additional variations such as eccentrics — by which the rotational axis was offset and not completely at the center — or adding epicycles to epicycles, were popular as well with astronomers.

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Ptolemy's unique contribution to this theory was the idea of an equant, which was a complicated addition which specified that when measuring the rotation of the Sun, one sometimes used the central axis of the universe, but sometimes used one set at a different location. This had an overall effect of making certain orbits "wobble", a fact which would greatly bother Copernicus (such wobbling would make the idea of material "spheres" in which the planets rotated implausible). In the end, after all of this complication, the astronomers could still not get observations and theory to match up with much reliability.

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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, even though he had arrived at it several decades earlier.

Related Topics:
De revolutionibus orbium coelestium - 1543

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This book marks the beginning of the shift 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; from the time of Galileo it has been recognized that for it not to point to the same place would be a motion.

Related Topics:
Geocentric - Anthropocentric - Planet - Year - Axis - Day - Equinox

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He also replaced Ptolemy's equant circles with more epicycles. This is the main source of the statement that his system had even more epicycles than Ptolemy's. With this change his system had only uniform circular motions, correcting what Copernicus 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.

Related Topics:
Ptolemy - Equant

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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 the time of publication until about 1700, there were very few astronomers who were convinced by the Copernican system, though the book was relatively widely circulated (around 500 copies are known to still exist, which is quite large by the scientific standards of the time). However, many astronomers accepted some aspects of his theory at the expense of others, and the system nevertheless had a large influence on later scientists such as Galileo and Johannes Kepler, who adopted, championed and (especially in Kepler's case) sought to improve the model. Galileo's observation of the phases of Venus produced, however, the first observational evidence for Copernicus' theory.

Related Topics:
Galileo - Johannes Kepler - Phases - Venus

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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:

Related Topics:
De revolutionibus - 1878

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• Orbits and celestial spheres do not have a unique, common, center.
• 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.
• 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.')
• The distance between the Earth and the Sun, compared with the distance between the Earth and the fixed stars, is very small.
• The daytime movement 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.
• The Earth (together with its Moon, and just like the other planets) moves around the Sun, so the movements that the Sun seems to be making (its apparent moving during daytime, and its annual moving through the Zodiac) are nothing else than effects of the Earth's real movements.
• These movements of the Earth and of the other planets around the Sun, can explain the stations, and all the particular characteristics of the planets' movements.

Whether these propositions were "revolutionary" or "conservative" has been a topic of some historical debate in the late twentieth century. Thomas Kuhn famously 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's work, and emphasized the importance and difficulty Copernicus would have had in putting forward a new astronomical theory relying on simplicity in geometry alone, given that he had no experimental evidence.

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De revolutionibus orbium coelestium

Main article: De revolutionibus orbium coelestium.

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The major work of Copernicus, "On the Revolution of Celestial 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 enclosed theory did not necessarily have to have implications outside the limited realm of astronomy. Copernicus' book itself began first with a letter from his (then deceased) friend, the Archbishop of Capua, urging Copernicus to publish his theory. In a lengthy introduction, Copernicus dedicated the book to Pope Paul III, explaining his apparent motivations as being related to the inability of previous 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 was an important issue at the time and one of the major reasons for Church funding of astronomy).

Related Topics:
1543 - Andreas Osiander - Capua - Pope Paul III - Calendar reform

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The work itself was then divided into six books.

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

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

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

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The fourth book contains a similar description of the Moon and its orbital movements.

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

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