« ... Johannes Kepler, in latin Keplerus, was born on December 27, 1571 in Weil, near Stuttgart. His mother Katharina Guldenmann, the daughter of an innkeeper, and his father Heinrich, an advocate of the Lutheran teaching under the banner of the Duke of Brunswick, followed the Duke of Alva as mercenaries. They fought against the Belgians. Meanwhile, little Johannes was abandoned to the care of his grandparents. A weak and sickly child, Johannes survived smallpox, but his hands were left crippled and his sight became weak. 

Kepler worked for some time in the inn his parents had opened after coming back from the war. He, even, underwent hard agricultural labour. In 1577 he started his studies at Leonberg. Then his talent induced his parents to allow him to enter the Adelberg convent school (1584). Afterwards he moved over to Maulbronn and four years later he started to attend the University of Tubingen. Under the instruction of Michael Maestlin, professor of mathematics and astronomy, he became deeply acquainted with the Copernican system. 

It was a period of great squabble between Catholics and Protestants. Kepler, though protestant, did not enter into such conflict, which he assumed preposterous. He repelled the "dull" attitude of the theologians and thus, changed his mind from theological studies and from his desire to count on an honourable carrier in the service of the Church. He accepted, instead, to become a teacher of mathematics in Graz (province of Styria) in April, 1594 and devoted himself to scientific studies. 

Two years later he published his first important work: "Prodromus" or "Mysterium cosmographicum" (The Cosmographic Mystery), in which he established a relation among the five regular solids and the number and distances of the known planets. The preface was his teacher’s Mastlin. Copies were sent to Brahe and Galileo. 

Brahe invited him to overlook his Tychonic system in light of his discoveries. Galileo sent him an interesting answer, regretting the climate of derision and dullness towards the hypotheses of Copernicus and worried because truth was neglected. 

This work emphasized Kepler’s first discovery, that drove him to relinquish the Ptolemaic system in favour of the Copernican system. It put in evidence that, if the Ptolemaic epicycles of the outer planets were observed from Earth, these would be seen from the same angle from which the orbit of the Earth is seen from a point in the orbit of each planet taken into consideration. It also explained the size of the epicycles of Mars, Jupiter, and Saturn. It further answered to questions left unanswered by the Ptolemaic system, that did not consider Earth’s annual motion. 

In this work, Kepler tried to find the law that regulated the distances of the single planets from the Sun. He followed the Neo-Platonic theories in the same way as Copernicus did and had well in mind Plato’s Timaeus: tempting to understand the universal order. A Neo-Platonism with a strong Pythagorean influence having its origin seated in mathematics. 

According to him, precise mathematical norms regulated nature. The scholar’s task was to understand them. With great satisfaction, he assumed to have discovered such rules and to have made them known to the world through his works in which he underlined both his confidence in the system discovered by Copernicus and in the existence of a Mathematical Mind. 

The regular, the platonic and the, so called, cosmic solids are the five solids mentioned in the "Mysterium". (67) Kepler imagined the universe as a gigantic "matrioska" into which the solids were nested, one into the other, progressively. Encased within each solid, the spheres of each planet. On the very outside part was the sphere of Saturn followed by the cube into which was the sphere of Jupiter; the tetrahedron encased the sphere of Mars; following the dodecahedron enclosed the Earth’s sphere; the icosahedron the sphere of Venus and the octahedron that of Mercury. As such, it was possible to know the size of the single spheres and the consequent reason that only six planets existed. 

Kepler believed God created the world with the use of mathematical rules; nature was regulated by intelligible laws and man had the possibility to understand the divine plan of creation. The simplicity of the system marked the truth and identified itself with harmony and beauty. 

The demiurge of Plato’s Timaeus geometrically perceived the world and overcame the Aristotle’s tradition and the mediaeval concept that dominated nature. Kepler’s deep and mystic Pythagoreanism became evident when he joined the distances between the planets and the Sun with the numerical ratios of the vibrant strings of the lyre. He called the Solar system "Lyra Apollinis", assuming the existence of a cosmic harmony into which each planet, in its evolution, sang one of the seven notes of the scale. 

Mathematics is the key to comprehension, both quantitatively and mystically. From a historical point of view, the idea of a nature that is systematically simple, is not always present. "Simplex sigillum veri", is a principle that is not acceptable for the believes of the Middle Ages or for those of the Romantic movement, where an untamed and cruel nature is accepted with great difficulty by a man overcome by it. 

Where Mystery and Bacchus are dominant, man is idle and unable to understand: sometimes discouraged and sometimes aware of his limits and forced to accept his impossibility to give positive answers. Trust in science and in the mission that a merciful God assigned to man, on the contrary, allows him to get lost in contemplation and to stubbornly try to understand and explain creation. 

Pythagoras, Plato and the cabbalistic convictions provided the instruments and, together with Kepler, shared the harmonic world, geometrically structured; a mythical ideal universe, that Kepler retained valuable. 

Only the perfect measurements of Brahe will force him to abandon the theory of an astral motion perfectly circular and to accept that of an elliptic motion, while taking into consideration the problem of the irregular motion of Mars, still not solved. A task on which he worked strenuously for ten long years, leaving us an enthusiastic description of his efforts. The elliptic motion gave the answer. The theory finally coincided with the empirical data. The planets orbited with variable velocities, regulated by a simple law. Once the mathematical solution was clear, the perfect circular motion dogma was definitively rejected. 

Year 1597 is the year of his marriage. Soon after the protestants started to be banished from Styria, following the visit the Archduke Ferdinand paid to Pope Clement VIII. 

On August 1600, Brahe invited Kepler to visit him in Prague, appointing him as his assistant. A year had not yet elapsed, when Tycho died (October 1601), and Emperor Rudolph II promoted Kepler "imperial mathematician", requesting him to complete the Rudolphine Tables. Kepler was secured a pay, half the salary of Tycho’s. 

The manuscript "Ad Vitellionem paralipomeni" was completed in 1604. The work dealt with geometrical optics, and was extremely important for the development of this science. In eleven chapters, Kepler defined light in a totally new way. He explained the process through which light reached the retina, thus recognizing the inverted image projected onto it. 

"Astronomia Nova", together with a long dedication to Emperor Rudolph II, was not published until 1609. This is Kepler’s most important work. In it, he studies the motion of Mars and formulates the first "two laws of Kepler". 

This work emphasizes the importance he assignes to the Sun (68), - seat of a magnetic force (69), probably drawing by analogy on William Gilbert’s theories, - and shows the efforts he went through to explain the Sun’s role. The Sun moves the planets. In it is the seat of a moving force (motive species), that seems radiating from something divine, comparable only to our soul. (70) 

Galileo, on March 1610, published the "Sidereus Nuncius" (Starry Messenger). This work, due to the many discoveries it described, arose great sensation. Kepler received a copy of the book through the agency of Giuliano de’ Medici, the Tuscan ambassador in Prague. Kepler’s first reaction was of disapproval. His Neo-Platonism did not accept that the primary role of the Sun should be minimized. Kepler’s intellectual honesty, however, arose soon after, when he confirmed the discoveries of Galileo, thanks to the telescope Galileo presented to Ernst of Cologne, Duke of Baviera, who, in turn, allowed Kepler to use it so that he could observe the moons of Jupiter. In addition, Kepler, also emphasized the importance of the telescope that, for some colleagues, among which Martin Horsky from Lochovic, (71) was worth nothing and unbecoming for philosophy.

Kepler’s "Dioptrice" was published in 1611. In this work is described all that may be observed through a telescope and was not observed before. This study opened a new horizon for observations with the support of this innovating instrument. The use and the function of different types of lenses is also described in this book. It helped optics to become an independent science. 

In 1611, after Rudolph II was forced to abdicate by his brother Matthias who, consequently, assumed the crown of Bohemia, Kepler left for Linz, invited by the Upper Austrian Lords. However, many personal troubles: his son Frederik’s death and, shortly after, that of his wife; the persecution to which he was exposed being charged for not being an orthodox; his exclusion from communion, upset his mind and thoughts. 

Kepler entered on a second marriage in 1613 and, in the same year, he also wrote "Nova stereometria doliorum vinariorum", a mathematical treatise in which he took into consideration a problem of extreme importance for his times. He studied how to measure the volume of containers, such as wine barrels, using an inventiveness that paved the way for the revolutionary method of the integral calculus. 

Again, ill luck struck on Kepler in 1616. His mother was accused with witchcraft. He was compelled to draw up legal defence against the Tubingen juridical faculty. Finally (1621) his mother was released, but she passed away soon after, as a result of hardship and "territio verbalis" (description of the torture) she underwent during her period of detention. 

Meantime, during these years he published his text on astronomy, in seven volumes, "Epitome Astronomiae Copernicanae" (Compendium of Copernican Astronomy), (72) where he applied his first two laws to the Moon, to the other planets and to Jupiter’s moons. In "Harmonices mundi libri V" he expounded his third law. 

As per above, in "Epitome" he once again considered the Sun and emphasized its beauty and dignity: hearth of the world; a carrier of warmth and light, enlightening human existence, with a motive power, similar to a magnet, able to move all celestial bodies. In his manuscript "Somnium" (The Dream) he proposed a theory where tides are originated by the attraction, both Sun and Moon have upon terrestrial waters. 

"Rudolphine Tables" were completed in 1627. The manuscript was a logarithm book of tables, used to calculate refraction. It also included a catalogue of 777 stars, that had already been observed by Tycho Brahe, to which others were added, increasing their number up to 1005. 

In 1628 Kepler travelled to Sagan, a Silesian town. He became official adviser to Albrecht Wallenstein, duke of Friedland. In Sagan his work "Ephemerides", a collection of data up to year 1626, went to press. Meanwhile, Wallestein entered into financial problems. Kepler, therefore, decided to reach Regensburg, where the Emperor had summoned a congress of Electors (Diet of Regensburg). Here he was in a position to discuss with many other men, with whom he was in friendly terms, about his big claim on the imperial treasury. His journey, anyway, was so tiring, that he fell ill and, following a fever attack, died far away from his family. As a Lutheran, he was interred outside the city walls. 

The spell Kepler originated is to be found in his philosophical creed. The same is not recognizable in Brahe. Kepler had a deep trust in man’s "ratio" and in man’s destiny. 

Contemplation of the universe means contemplation of the divine itself, but man’s efforts do not end here. Man has the capability to understand; has the means, the arguments and the consciousness to satisfy this longing. Kepler was a strange type of scientist, morally unassailable. His reasoning was clear; his nature gentle. He was honest and, at the same time, he was a mystic, deeply religious man, even if not orthodox. Astronomy was his "creed": a need, a task for the learned man. For him it involved both physical evidence together with a universe deeply religious, with plenty of values. 

In its perfection, or in the faith for such a perfection, he created an extremely divine image of the world with a soul, similar to the soul "motrix" of the Sun, the most important celestial body in the universe, as per the hermetic theories. A static order, the mathematician can understand, once it is correctly decoded: Pythagoras and the scholar of the seventeenth century come together and become one 
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