One could risk to claim, that each rational practice of natural sciences should necessarily begin with a thorough study of the works of Johannes Kepler, who became an extremely important figure not only for the development of astronomy, but for the whole science and civilization. The vision of the world, which Kepler has created and developed, is one of the most unusual in the history. It contains elements which have become over time the common intellectual property of mankind.
For a long time Kepler was poorly understood and not popular scientist. Selected Kepler's scientific achievements were early usurped by Isaac Newton and published, among others in his famous Principia. If one said that it is unnecessary to recourse to the original Kepler's works, since the same contents are given by Newton in more precise manner, one would be wrong. Kepler's achievements are many times richer than even Newton was able to understand. Many very basic scientific considerations were initiated by Kepler, but never completed by anyone. Moreover, from Kepler we can constantly learn how to penetrate the secrets of nature, because, unlike the others, he meticulously described his methods.
For experts of the scientific enlightenment, which took place in the sixteenth and seventeenth century, it is clear that Kepler takes a leading place among such scholars like Copernicus, Tycho de Brahe, Galileo and Newton. However, it often happens that authorities are not aware about this and highlight others - Copernicus, Galileo and Newton, forgetting the greater Kepler.
In 1609 Johannes Kepler published his work Astronomia Nova, which introduced the modern way for investigating the truths of nature, based on detailed analysis of observational data. Astronomia Nova includes the first two laws of planetary motion, derived from very careful analysis of Mars observations. The Kepler’s laws gave foundation for modern celestial mechanics and modern science in general. They are universal, accurate and verifiable.
In the year 1600, Kepler was hired in Prague as an assistant of the imperial astronomer Tycho de Brahe. He analyzed, obtained by Tycho and the most accurate at that time, long-term observations of the positions of Mars. After Tycho's death, in 1601, Kepler was appointed to the position of imperial astronomer in Prague and in 1605 he discovered that Mars moves on elliptical orbit around the Sun, and not on a circle! Moreover, the Sun is at one focus of the ellipse, and not at its center. Attempts to fit different egg-like shapes to the observation points almost led Kepler to madness. He won his "war with Mars" only by using the ellipse. Earlier, in 1601, Kepler discovered that Mars moves around the Sun in such a way that the segment connecting the planet with the Sun sweeps equal areas in equal time intervals. The first historical record of the conservation of angular momentum principle today bears the name of the second Kepler’s law. This regularity has facilitated the discovery of the elliptical shape of the orbit of Mars - the first Kepler’s law.
After dealing with the orbit of Mars, Kepler checked if same laws govern other planets orbiting the Sun. To his enormous satisfaction, he observed the same phenomenon. This way Kepler became absolutely sure about his discoveries.
He believed that the Sun is the reason for the planetary motion. Looking for the nature of force “emitted” by the Sun through the analysis of movements of planets he discovered his third law, which connects stellar orbital period of planet circulating around the Sun with its average distance from it. The third law of planetary motion Kepler discovered on May 15th 1618 and published in the work Harmonice Mundi in 1619: "it is absolutely sure, that the ratio of the circulation periods of any two planets, is exactly equal to the ratio of their average distance raised to the power 3/2".
Kepler discovered three laws, which to this day are taught at school. It is Kepler's achievements, not the legendary apple, which helped Newton to formulate the law of universal gravitation, lying at the basis of modern space exploration. The three laws of planetary motion are however not the only scientific achievements of Kepler. In addition to such immortal works as Astronomia Nova and Harmonice Mundi Kepler wrote 22 other fundamental works to enable development of modern science.
Among them he laid foundations for modern optics. He explained the image formation using camera obscura and the human eye, he described how to make glasses for myopic and long-sighted people and explained why two eyes are necessary to sense the distance of objects at sight. He described the formation of the real, virtual, upright and inverted optical images and characterized image magnification in optics. He explained the phenomena of refraction, total internal reflection and developed a theory for construction of an astronomical telescope.
Kepler showed that tides are caused by the Moon. He tried to use the parallax induced by cirulation of the Earth around the Sun to measure the distance of stars being suggested by the analogy to the perception of depth by two eyes positioned next to each other. He suggested that the Sun rotates around its axis, and introduced the concept of causality in astronomy, claiming that the Sun drives the movements of the planets. He calculated Rudolfine Tables (describing expected positions of planets), which the extraordinary accuracy was the most eloquent argument for the correctness of the heliocentric theory. He invented logarithms and formulated the basics of integral calculus. In 1604 Kepler observed and described supernova in Ophiuchus. He also wrote the first science fiction novel (Somnium, about the flight to the Moon). From him came such words like: orbit, satellite and diopter.
Kepler was heavily inspired by the heliocentric theory of Copernicus. Similarly to Copernicus he was a deeply religious man. By his scientific work he was fulfilling the duties of a Christian for better understanding of God through understanding the work of the creation - the Universe. He thought, that if one better knows the nature, one better understands God, who reveals himself in nature the most. Nature was seen by Kepler as the second Book of Revelation, which is an indispensable complement to the Bible: "its letters are the stars, its words are cosmic structures and geometry allows better understanding the importance of the content." In accordance with his belief that nature is the image of God, Kepler was searching for an active spirit in every corner of the Universe. He considered himself and other astronomers "the priests of God in field of interpretation of the Book of Nature".
Kepler had a remarkable life. He liked to think of himself in terms of providential coincidences that made him early encountered with the Copernicus theory, that he didn’t became a theologian, but an astronomer, and that he finally met in his life Tycho de Brahe and due to his observations Kepler could make the greatest reform of astronomy since the days of Ptolemy. Of course, all this could not happen without Kepler's creative imagination combined with respect to facts. Kepler was a genius, one of the largest in the history of science. His biography however, seems even more remarkable when we consider how little was lacking, that he would never get education, and how important was his raising in excellent educational system of Württemberg and that he could develop his talents instead of eg. crafts.
Kepler was born on December 27th 1571 in Weil der Stadt and died on November 15th 1630 in Regensburg. The last two years of his creative life he spent in Żagań, near Zielona Góra. Through his extraordinary achievements he constantly lives in memory of posterity.