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The apparent retrograde motion of the planets is caused by the motion of the Earth from which one observes.

Some have noted that 2, 4, 5, and 7 can be deduced from 3 and 6 but it was never Copernicus's aim to give a minimal set of axioms. The most remarkable of the axioms is 7, for although earlier scholars had claimed that the Earth moved, some claiming that it revolved round the sun, nobody before Copernicus appears to have correctly explained the retrograde motion of the outer planets. Even when he wrote his Little Commentary Copernicus was planning to write a major work, for he wrote in it (see ):-

Here, for the sake of brevity, I have thought it desirable to omit the mathematical demonstrations intended for my larger work.

It is likely that he wrote the Little Commentary in 1514 and began writing his major work De revolutionibus in the following year.

Given Copernicus's nature it is clear that he would have liked to have lived a quiet life at Frauenburg, carrying out his (relatively few) duties conscientiously and devoting all his spare time to observing, developing his theories of the universe, and writing De revolutionibus. It is equally clear that his fame as an astronomer was well known for when the Fifth Lateran Council decided to improve the calendar, which was known to be out of phase with the seasons, the Pope appealed to experts for advice in 1514, one of these experts was Copernicus. Many experts went to Rome to advise the Council, but Copernicus chose to respond by letter. He did not wish to contribute more to the discussions on the calendar since he felt that the motions of the heavenly bodies was still not understood with sufficient precision.

The peace which Copernicus wished, however, was not easy to find in a period of frequent wars. The fortifications of Frauenburg that formed Copernicus's home had been built to protect the town which had been captured by various opposing groups over the years. In 1516 Copernicus was given the task of administering the districts of Allenstein (also known as Olsztyn) and Mehlsack. He lived for four years in Allenstein Castle while carrying out these administrative duties.

You can see a picture of  Allenstein Castle where Copernicus lived.

Always keen to make observations, Copernicus returned to his home/observatory in Frauenburg whenever there was a reason to attend a meeting or consult with the other canons, always taking the opportunity to further his researches. However when war broke out between Poland and the Teutonic Knights towards the end of 1519 Copernicus was back in Frauenburg. After a period of war, Copernicus was sent to participate in peace talks in Braunsberg as one of a two man delegation representing the Bishop of Ermland. The peace talks failed and the war continued. Frauenburg came under siege but Copernicus continued making his observations even at this desperate time. By the autumn of 1520 Copernicus was back living in Allenstein Castle and had to organise its defence against attacking forces. The castle resisted the attack and by 1521 an uneasy peace had returned.

As a reward for his defence of Allenstein, Copernicus was appointed Commissar of Ermland and given the task of rebuilding the district after the war. His close friend, Tiedemann Giese, another canon in the Chapter, was given the task of assisting him.

You can see a picture of  Tiedemann Giese.

As part of the recovery plan, Copernicus put forward a scheme for the reform of the currency which he presented to the Diet of Graudenz in 1522. However, despite attending the Diet and arguing strongly for his sensible proposals, they were not acted on.

Copernicus returned to Frauenburg where his life became less eventful and he had the peace and quiet that he longed for to allow him to make observations and to work on details of his heliocentric theory. Having said that he now had the peace he wanted, one should also realise that he was undertaking his mathematical and astronomical work in isolation with no colleagues with whom to discuss matters. Although Copernicus was a canon, he had never become a priest. In fact on 4 February 1531 his bishop threatened to take away his income if he did not enter the priesthood, yet Copernicus still refused.

A full account of Copernicus's theory was apparently slow to reach a state in which he wished to see it published, and this did not happen until the very end of Copernicus's life when he published his life's work under the title De revolutionibus orbium coelestium (Nuremberg, 1543). In fact had it not been for Georg Joachim  Rheticus, a young professor of mathematics and astronomy at the University of Wittenberg, Copernicus's masterpiece might never have been published. In May 1539  Rheticus arrived at Frauenburg where he spent about two years with Copernicus.  Rheticus wrote of his visit:-

I heard of the fame of Master Nicolaus Copernicus in the northern lands, and although the University of Wittenberg had made me a Public Professor in those arts, nonetheless, I did not think that I should be content until I had learned something more through the instruction of that man. And I also say that I regret neither the financial expenses nor the long journey nor the remaining hardships. Yet, it seems to me that there came a great reward for these troubles, namely that I, a rather daring young man, compelled this venerable man to share his ideas sooner in this discipline with the whole world.

We should note that  Rheticus was a Protestant, so in those troubled times of the Reformation he took somewhat of a risk visiting a Catholic stronghold. In September 1539  Rheticus went to Danzig, visiting the mayor of Danzig, who gave him some financial assistance to help publish the Narratio Prima or, to give it its full title First report to Johann Schöner on the Books of the Revolutions of the learned gentleman and distinguished mathematician, the Reverend Doctor Nicolaus Copernicus of Torun, Canon of Warmia, by a certain youth devoted to mathematics. The publication of this work encouraged Copernicus to publish the full mathematical details of his theory which he had promised 27 years earlier. Swerdlow writes:-

Copernicus could not have asked for a more erudite, elegant, and enthusiastic introduction of his new astronomy to the world of good letters; indeed to this day the "Narratio Prima" remains the best introduction to Copernicus's work.

In his First Report  Rheticus wrote about Copernicus's way of working (see ):-

... my teacher always had before his eyes the observations of all ages together with his own, assembled in order as in catalogues; then when some conclusion must be drawn or contribution made to the science and its principles, he proceeds from the earliest observations to his own, seeking the mutual relationship which harmonizes them all; the results thus obtained by correct inference under the guidance of Urania he then compares with the hypothesis of  Ptolemy and the ancients; and having made a most careful examination of these hypotheses, he finds that astronomical proof requires their rejection; he assumes new hypotheses, not indeed without divine inspiration and the favour of the gods; by applying mathematics, he geometrically establishes the conclusions which can be drawn from them by correct inference; he then harmonizes the ancient observations and his own with the hypotheses which he has adopted; and after performing all these operations he finally writes down the laws of astronomy ...

While living with Copernicus,  Rheticus wrote to several people reporting on the progress Copernicus was making. For example on 2 June 1541  Rheticus wrote that Copernicus :-

... is enjoying quite good health and is writing a great deal ...

while he wrote that on 9 June Copernicus :-

... had finally overcome his prolonged reluctance to release his volume for publication.

By 29 August De revolutionibus orbium coelestium was ready for the printer.  Rheticus took the manuscript with him when he returned to his teaching duties at Wittenberg, and gave it the printer Johann Petreius in Nürnberg. This was a leading centre for printing and Petreius was the best printer in town. However, since he was unable to stay to supervise the printing he asked Andreas Osiander, a Lutheran theologian with considerable experience of printing mathematical texts, to undertake the task. What Osiander did was to write a letter to the reader, inserted in place of Copernicus's original Preface following the title page, in which he claimed that the results of the book were not intended as the truth, rather that they merely presented a simpler way to calculate the positions of the heavenly bodies. The letter was unsigned and the true author of the letter was not revealed publicly until  Kepler did so 50 years later. Osiander also subtly changed the title to make it appear less like a claim of the real world. Some are appalled at this gigantic piece of deception by Osiander, as  Rheticus was at the time, others feel that it was only because of Osiander's Preface that Copernicus's work was read and not immediately condemned.

In De revolutionibus Copernicus states several reasons why it is logical that the sun would be at the centre of the universe:-

At the middle of all things lies the sun. As the location of this luminary in the cosmos, that most beautiful temple, would there be any other place or any better place than the centre, from which it can light up everything at the same time? Hence the sun is not inappropriately called by some the lamp of the universe, by others its mind, and by others its ruler.

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