“The very famous and very learned Nicolaus Copernicus, incomparable astronomer” was canon of Warmia – a province governed by his uncle and tutor, Bishop Luis Watzelrode. Copernicus was born in Torun in 1473 and died in 1543, the same year that his most important work was published. “De revolutionibus orbium coelestiun”. Copernicus made very few astronomical observations personally. He first studied at the University of Krakow – the capital at that time of his homeland: Poland. Later he expanded his studies at the Italian universities of Bologna and Padua where he made contact with Renaissance environments. His contact with the Florentine Neoplatonists is the origin of his heliocentric conception of the world.

The Copernican system

Heliocentric representation of the planets known in Copernicus’ time, as drawn in his book “De revolutionibus orbium coelestium”:

I. Immobile sphere of fixed stars.

II. Saturn makes one complete revolution every 30 years.

III. Jupiter every 12 years.

IV. Mars every 2 years.

V The Earth, together with the Moon, every year

VI. Venus every 9 months.

VII. Mercury every 80 days. The Sun is, in the model of Copernicus, located in the center of the Universe and of the orbits of the planets, the earth is only one of them.

The ecliptic movement of the Sun

The image represents an observational data explained according to the geocentric model of Ptolemy and according to the heliocentric model of Copernicus. The observational data is the apparent annual movement of the Sun through its ecliptic. The Sun performs a regressive movement through the Zodiac.

The movement that depends on the Sun, Mercury and Venus

The so-called lower planets – Mercury and Venus – have a movement always linked to the Sun from which Mercury is not separated by more than 23º and Venus more than 44º. Ptolemaic Astronomy explained this observation by linking the deferents of both planets to that of the Sun, so that the center of the epicycle of the planet was constantly maintained on a line that passes through the Earth and the Sun. Copernicus explained the movements of these planets in a way simpler and more natural.

Retrograde of the superior planets

In the Copernican system the planets retrograde when their movement takes them to occupy the point of their trajectory closest to the Earth. This moment is also when the planet shines the brightest. Ptolemaic Astronomy – geocentric – also explained these phenomena, but it needed to resort to epicycles, which the Copernican system did not need to explain its qualitative aspects of planetary movements.

Retrogradation of the lower planets

This drawing, taken like the previous ones from Norwood Russell Hanson’s posthumous book “Constellations and conjectures”, explains in an original way the apparent backward movement of the lower planets and how the same appearances are saved differently depending on that the explanation is heliocentric or geocentric. Stellar parallax One of the strongest arguments in favor of the immobility of the Earth and, therefore, against the Copernicus system, was the absence of stellar parallax. If the constellations are in the stellar sphere and if the Earth is moving, then changes in the configuration of the constellations, that is, in the relative positions of the stars, would have to be observed. Now, the configurations do not change and on the other hand the celestial sphere is at a finite distance, as shown by the rotation around us in a finite time. Therefore the Earth does not move. The only counter argument was given by Copernicus: “the distance from the Earth to the Sun is practically negligible compared to the magnitudes of the firmament.” The stellar parallax is therefore invaluable. The argument allowed only three options: deny heliocentrism, deny the finiteness of the distance to the stars, or hope that greater precision in astronomical instruments would finally detect parallax. Stellar parallax was not detected until 1838 by Friedric Wilheim Bessel.