2 The Copernican heliocentric system

2.1 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.

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".

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.

2.2 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.

This book marks the beginning of the shift from a geocentric (and anthropocentric ) universe with the Earth at its centre. 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.

He also replaced Ptolemy's equant circles with 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 seemed to be a defect in Ptolemy's system. Unfortunately, uniform circular motion is not what happens in the solar system, which runs on elliptical orbits; and this model was no more precise in predicting ephemerides than the then current tables based on Ptolemy's model. Furthermore, he badly underestimated the size of the solar system, like most of the astronomers of the time.

The system nevertheless had a large influence on scientists such as Galileo, Tycho Brahe, and Johannes Kepler, who adopted, championed and (especially in Kepler's case) improved the model. Galileo's observation of the phases of Venus produced, however, 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, centre.
2. The centre of the Earth is not the centre of the Universe, but only the centre of the Earth's mass and of the lunar orbit.
3. All the planets move along orbits whose centre is the Sun, therefore the Sun is the centre of the World. (Copernicus was never certain whether the Sun moved or not, claiming that the centre 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 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.
6. The Earth (together with its Moon, and just like the other planets) moves around the Sun, so the movements that the Sun seems making (its apparent moving during daytime, and its annual moving through the Zodiac) are nothing else than effects of the Earth's real movements.
7. 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.

These propositions represent the exact contrary of what the dominant geocentric propositions stated.

2.3 De Revolutionibus Orbium Coelestium

Main article: De Revolutionibus Orbium Coelestium.

The work of Copernicus, "On the Revolution of Celestial Spheres" ( 1543), dedicated to the Pope Paul III, is divided into 6 books.

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

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).

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

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

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

3 Copernicus and Copernicanism

Copernicus' theories have an extraordinary relevance in the history of human knowledge. Many authors suggest that only Euclidean geometry, Charles Darwin's Evolutionism, or Newton's physics could have a similar influence on human culture in general and on science in particular.

Many meanings have been seen in his theory, quite apart from its scientific value. His work cut across science and religion, dogmatism and freedom of scientific investigation. His academic standing is often compared with Galileo.

When his work was published, it contradicted then accepted religious dogma: the suggestion being that there is no need for an entity (God) that from outside could give a soul, a power and a life to the World and to Human beings when science can explain everything attributed to Him.

However, Copernicanism also opened a way to immanence, the view that the divine force, or the divine being, pervades through all things that exist, which has been developed further in modern philosophy. Immanentism also leads into subjectivism: the theory that perception creates reality, and that there is no underlying, true, reality that exists independent of perception. Accordingly some find that Copernicanism demolished the foundations of mediaeval science and metaphysics.

One of the consequences of Copernicanism is that scientific laws must not necessarily coincide with appearance. This contrasts with Aristotle's system, which placed much more value on knowledge gained from the senses.

Copernicus' innovation was a scientific revolution. Some say "the" revolution ([1]). Immanuel Kant, for instance, caught the symbolic character of Copernicus' revolution (of which he put in evidence the trascendental rationalism) postulating that human rationality was the real legislator of observed phenomena. More recent philosophers also have found Copernicanism to remain valid and retain valuable philosophical meaning.

4 Discussion

Copernicus' lived in early 16th century Prussia and Poland, and was influenced by the cultural, religious, and social contexts of life at the time. He was well educated. At the University of Kraków, which he attended in 1491 and 1492, Copernicus studied both mathematics and astronomy in common with all university students of that time. There is evidence that his interest in these subjects continued after he had left Kraków.

The Earth-centred Ptolemaic cosmology had been the accepted model of the universe since the 2nd century BC. Ptolemy's model explained each planet's circular motion individually and was the first model of the universe to explain some of the eccentric behaviour of the planets. It maintained that all planetary motion, and the motion of the Moon, the Sun, and the stars was circular, around a stationary Earth.

An accurate calculation of the astronomical year was important to a clergyman, like Copernicus, allowing him to forecast properly the various festivals that comprised the liturgical calendar. The mathematical confusion that Copernicus said caused him to develop an alternative to the geocentric model derived from an inadequate reconciliation of the Aristotelian model and amendments to it by Ptolemy.

The Ptolemaic geocentric model was complicated and inconsistent in Copernicus' estimations and observations, including one in 1497 of the star Aldebaran, that did not coincide with predictions made by Ptolemy. Nor did the Ptolemaic model explain precession. Precession is the phenomenon by which the Earth's axis "wobbles". This characteristic of the Earth's movement is apparent only with observation over long periods of time. In Copernicus' view, Ptolemy's explanation failed to provide an accurate mathematical description of the universe. His heliocentric universe theory accomplished this by dispensing with individual explanations for the motion of each planet, and replacing them with a description that applied to all the planets, including the Earth.

Copernicus' mathematical experience engendered in his thought a desire for a simpler and more elegant model of the universe. He was acquainted with ideas espoused by other classical authors. Some of the ideas expressed by Philalaus ( 5th century BC) and Heraclides ( 4th century BC), proposed cosmological models in which the Earth moved. Aristarchus ( 3rd century BC) proposed an openly heliocentric model of the universe. Heraclides' description of the revolutions of Mercury and Venus around the Sun might have led Copernicus to consider that the other planets, including the Earth, did the same.

Elegance was a consequence of the overall simplicity of Copernicus' cosmology and much of this seeming simplicity resulted from his retention of circular orbits for the planets around the central Sun. Copernicus used the eccentrics, epicycles, and equants of Ptolemaic cosmology, but added three kinds of motion to describe the observed behaviour of the Earth:

• Annual motion — the yearly orbit around the Sun
• Daily rotation — the motion around a tilted axis that results in day and night
• Precession — the axial wobble mentioned earlier that explains why the position of the fixed stars seems to change over long periods of time.

Until 1543, the year that Copernicus died, and the year in which his de Revolutionibus was published, and for many years afterwards, Copernicus' description of the motion of the Earth was not ratified by empirical evidence. In his unauthorized and anonymous preface to de Revolutionibus, Andreas Osiander was technically correct when he made reference to "the hypothesis of this work". However, its consistency with the observed behaviour of the universe in a time before the telescope made more detailed observation and the gathering of more accurate measurements practicable, gave the Copernican model its strongest support. Not much more than a century later, Kepler had certainly despatched the circular orbits of the planets and replaced them with ellipses, but the Copernican heliocentric universe was still intact.

In his own preface to his work, dedicated to Pope Paul III, Copernicus took care to point out that his motives for developing a cosmology that included a moving, rather than a stationary, Earth, were inspired by his dissatisfaction with the mathematical and astronomical descriptions of the geocentric model, and were not intended to defy the written Word. "Mathematics", he says, "is written for mathematicians". Copernicus seems to have been benefited from the attitude of the bishops who were his superiors in the church - Johann Dantiscus and Tiedmann Giese . Both preferred, at least initially, to promote tolerance of differing views within the church rather than open discord, and both encouraged Copernicus' publication of his scientific beliefs. However, the lenient attitudes in Chelmno, where Copernicus carried out much of his work, began to change and might have contributed to Copernicus' isolation in the last years of his life. For orthodox Catholics, the Copernican model of the universe might have seemed too radically different from the geocentric model, sustained as it was by its agreement with many scriptural references. They might not have been ready to change to an understanding of the Bible as a source only of moral and spiritual, rather than scientific, wisdom.

As far as Copernicus was concerned, the Sun, a distinctive element in classical thought, held the central and most important position in the universe, gave added credence to his cosmology. His reverence for the sun can be seen in the most famous passage of de Revolutionibus:

"In the centre of all rests the Sun. For who would place this lamp of a very beautful temple in another or better place then this from which it can illuminate everything at the same time? As a matter of fact, not unhappily do some call it the lantern; others, the mind, and still others, the pilot of the world. Trismegistus calls it a 'visible God'; Sophocles' Electra, 'that which gazes upon all things.' And so the Sun, as if resting on a kingly throne, governs the family of stars which wheel around."

In this discussion of Copernicus' reasons for discarding such a long-held belief as the geocentric cosmology of Ptolemy, we can see that the Copernican revolution was simmering against a background revolution of theological thought — the Reformation. Neo-Platonic and classical ideas formed the intellectual environment in which Copernicus worked. Although not holding ordained office within the Catholic Church, Copernicus was devout and unwilling to be openly defiant of the Church's teaching, but, in common with supporters of the Reformation, Copernicus was criticizing orthodox theory and belief. His reasons for doing so lay in his dissatisfaction with the inadequacies of the geocentric model, in his strong belief in the truth of the solution to the problem that he developed, its elegance and relative simplicity, and its coincidence with observation and with the classical ideals to which he had subscribed since his youth.

5 Quotes

Goethe:

"Of all discoveries and opinions, none may have exerted a greater effect on the human spirit than the doctrine of Copernicus. The world had scarcely become known as round and complete in itself when it was asked to waive the tremendous privilege of being the centre of the universe. Never, perhaps, was a greater demand made on mankind - for by this admission so many things vanished in mist and smoke! What became of our Eden, our world of innocence, piety and poetry; the testimony of the senses; the conviction of a poetic - religious faith? No wonder his contemporaries did not wish to let all this go and offered every possible resistance to a doctrine which in its converts authorized and demanded a freedom of view and greatness of thought so far unknown, indeed not even dreamed of."

Copernicus:

For I am not so enamored of my own opinions that I disregard what others may think of them. I am aware that a philosopher's ideas are not subject to the judgement of ordinary persons, because it is his endeavor to seek the truth in all things, to the extent permitted to human reason by God. Yet I hold that completely erroneous views should be shunned. Those who know that the consensus of many centuries has sanctioned the conception that the earth remains at rest in the middle of the heaven as its centre would, I reflected, regard it as an insane pronouncement if I made the opposite assertion that the earth moves.

For when a ship is floating calmly along, the sailors see its motion mirrored in everything outside, while on the other hand they suppose that they are stationary, together with everything on board. In the same way, the motion of the earth can unquestionably produce the impression that the entire universe is rotating.

“Therefore alongside the ancient hypotheses, which are no more probable, let us permit these new hypotheses also to become known, especially since they are admirable as well as simple and bring with them a huge treasure of very skillful observations. So far as hypotheses are concerned, let no one expect anything certain from astronomy, which cannot furnish it, lest he accept as the truth ideas conceived for another purpose, and depart from this study a greater fool than when he entered it. Farewell.”

See also: inferior planet, superior planet

6 Reference

DC Goodman, CA Russell, eds. The Rise of Scientific Europe 1500-1800. Bath, UK: Hodder &

7 External links

Wikiquote has a collection of quotations by or about .

• Nicholaus Copernicus Museum in Frombork
• Portraits of Copernicus: Portrait; Nicolaus Copernicus
• Copernicus and Astrology - A reliable website from Cambridge University describing Copernicus' astrological activities.
• The Copernican Universe from the De Revolutionibus
• De Revolutionibus, 1543 first edition - Full digital facsimile, Lehigh University.
• De Revolutionibus, autograph manuscript - Full digital facsimile, Jagiellonian University.
• The front page of the De Revolutionibus
• The text of the De Revolutionibus
• A link collection
• A java applet about Retrograde Motion
• Copernicus in Bologna - in Italian
• "Chasing Copernicus: The Book Nobody Read". - Was One of the Greatest Scientific Works Really Ignored?. All Things Considered, NPR. March 4, 2004.
• Copernicus Foundation Chicago
• Copernicus University in Torun

Copernicus, Nicolaus Copernicus, Nicolaus Copernicus, Nicolaus Copernicus, Nicolaus Copernicus, Nicolaus

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