He discovered that the planets revolved in elliptical rather than circular orbits: Who is Johannes Kepler?

Johannes Kepler was born on December 27, 1571, in Weil der Stadt, in the German state of Würtenberg, as the eldest of seven children. When Kepler calculated the time of conception using astrological principles years later, he concluded that he was born as a 7-month-old premature baby.

The inter-sectarian conflicts that would affect Kepler's life in the future had been going on for 50 years when he was born. In the religious turmoil that ensued at the time, the Kepler family found themselves in the unusual situation of being members of a Protestant minority. Religious issues play a large part in Kepler's education.

Johannes Kepler (27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws of planetary motion, and his books Astronomia nova, Harmonice Mundi, and Epitome Astronomiae Copernicanae. These works also provided one of the foundations for Newton's theory of universal gravitation.

His tough, grumpy father, Heinrich, goes to the Netherlands to fight as a mercenary for adventure before his son is 3 years old. This is repeated throughout Kepler's childhood. Finally, in 1588, when Kepler was 16, he left, never to return, and despite rumors that he had died, no one could find out the truth. Kepler was raised by his mother and is similar to his mother in many ways. Like him, he is dark and small, with a restless and curious mind. His mother did not go to school but is interested in herbs and home remedies.

Although he went to the traditional German school first, he later switched to the Latin school. An interesting point about Kepler's education is that although his Latin style was quite good, he never learned to write his mother tongue German in the same way. From the age of 8 to 10, he works in the fields with his family. Because he is a small and weak child, he is not suitable for working in the fields and is enrolled in school again. Bypassing the state examinations and being accepted to the lower seminary in Adelberg on October 16, 1584, he takes an important step in his education, as this is the first of the 2 stages that lead to university entrance. Two years later he is promoted to the upper seminary in the former Cistercian monastery in Maulbronn.

He is successful in school, besides, he is interested in poetry and enjoys jokes and puzzles. He uses anagrams and acrostics in many of his poems. He selects and memorizes the longest hymns to train his memory. Kepler takes religious lessons very seriously, and does not immediately accept what he is taught on this subject, he wants to find the answer himself.

Kepler reached the zenith of his efforts at school when he passed the University of Tübingen's graduation exam on September 25, 1588. He has been a registered student at the University of Tübingen for almost 1 year, although he is still at the upper seminary in Maulbronn. Tübingen is a historic university town in the German state of Baden-Württemberg. At the University of Tübingen, Kepler took mathematics and astronomy lessons from Michael Maestlin, one of the leading astronomers of the time with the stern and rough appearance he admired, becoming his favorite student. Maestlin makes his young student read Copernicus' De Revolutionibus. Unlike his author, Kepler felt the need to investigate not only the mathematical explanation of planetary motions but also their physical and metaphysical justifications. While still a student in 1590, Kepler began to think that the heliocentric model of the universe was God's mathematical plan. While still a student, he writes: “(…) Among all the bodies in the universe, the highest and greatest is the Sun, whose essence is pure light. The sun alone is the source that creates, protects, and heats everything.”

At the beginning of September 1590, Duke Ludwig selected 5 students on scholarship to the Faculty of Theology at the University of Tübingen, among them Kepler. As Kepler's theology studies progressed, on August 11, 1591, he completed the 2-year advanced study he had to complete at the Faculty of Letters and received his master's degree. Kepler would become a clergyman after graduating from college, but in early 1594 a drastic change occurred that spoiled the plans. He is appointed by his university as a mathematics teacher at a school in Graz, in the south of Austria, and attends. In fact, he does not want to be a mathematics teacher, moreover, he does not think that he has a special talent for mathematics. He is not a very good teacher, stutters are shy, and sometimes incomprehensible even in what he is saying. In the classroom, it is difficult to even attract the attention of students.

He earns little money while teaching and earns his living by reading the fortunes of the nobles. Kepler disdains some aspects of astrology but considers it an ancient and valid science. He always opens his horoscopes, from which he earns a regular income, throughout his life. When he comes to Graz, he prepares a calendar that informs the events in advance. In his first prediction, he predicted severe cold weather, the Turks attacking Austria from the south, and a peasant uprising. Coincidentally, his predictions of the weather and peasant uprisings turn out to be correct (although his later prophecies weren't quite correct), thereby earning him an almost legendary reputation in the region. However, Kepler cannot stay long in Graz, where he finds a comfortable working environment, and is forced to leave the city with the Protestant minority, which succumbed to religious strife.

According to Plato, nature consists of five elements. Each element can be symbolized by regular polyhedra. According to him, four-sided (tetrahedron) symbolizes fire, six-sided (hexahedron) earth, eight-sided (octahedron) air, twelve-sided (dodecahedron) universe, and twenty-sided (icosahedron) water. Because of this thought of Plato in his Timaeus, these shapes are called Platonic Bodies. Kepler, while teaching at the University of Graz in 1595, believed that the solar system or the six planets known at that time should act in perfect harmony and thought to defend this idea. He makes an explanation that Plato's geometric shapes can be used to describe the movements of the 6 planets. According to Kepler, all these two-sided geometric figures can explain the movements of the planets in the sky.

Coming nearly 50 years after Copernicus' De Revolutionibus Orbium Coelestium (On the Rotations of the Celestial Bodies), this book is the first work after Copernicus to defend his system. In his book, Kepler explains by example that he thinks God has a geometrical universe plan. He also comments on why and how fast the planets move, and why they slow down as they move away from the Sun. In the Copernican model, the Sun is in the center. The sun illuminates all the planets, but it does not rotate the planets. Kepler takes a big step forward, arguing that the Sun at the center also causes the planets to move. According to him, the Sun, the source of all light and heat, must be not only the structural but also the dynamic center of the universe.

Kepler met Barbara Müller on February 9, 1597, and they married, despite the opposition of Müller's father. His wife has a daughter from her first marriage. The couple had a son named Heinrich on February 2, 1598, but only lived for 2 months. In June 1599, a daughter, named Susana, was born, and they lost her, unfortunately, 35 days later. Kepler refuses the Catholic burial and is fined. He describes his wife as a stupid, sullen, melancholic person who cannot overcome his loneliness. “My work sometimes makes me absent-minded. However, I learned to be patient with him. When I saw that my words were taken away, I would rather sit down and bite my finger than insult him.”

His teacher, Michael Maestlin, was greatly influenced by Kepler's first book. At his insistence, the young Kepler sent his book to many astronomers. His contemporary, Galileo Galilei, only congratulates Kepler for his Copernican views. Danish astronomer Tycho Brahe, on the other hand, liked the book very much and took Kepler, who left Graz and became unemployed, as his assistant. Kepler begins work at Brahe's observatory near Prague in 1600. His official duty there was to advise the Holy Roman Emperor Rudolf on astrology and to prepare astronomical charts for him, which would later be called the Rudolf Tables.

Tycho Brahe does not intend to present the fruits of his life's work to a much younger rival but is stingy with Kepler, who is burning with a passion for learning. They fight often and makeup again. Brahe is also known for wearing a gold and silver prosthesis after losing his nose in a duel in his youth. Brahe dies 11 days after having dinner at the palace of Baron Rozmberk. There are different opinions, such as that he was poisoned, obeyed the rules of the period during the meal, did not go to the toilet, and his bladder exploded. However, in Kepler's article on Tycho's death, he died of a urinary tract infection, according to modern-day scientists.

Upon Brahe's unexpected death in 1601, Kepler became an imperial astronomer by Emperor Rudolf II. Brahe assigned Kepler the task of studying Mars in his research group. But he first comes to the conclusion that it is necessary to examine the phenomenon of refraction of light in the atmosphere. During these years, he also started working in the field of optics. He provided the first mathematical theory of the dark box (camera obscura) and the first correct explanation of the workings of the human eye (in the form of an image falling upside down on the retina). In 1604 he published the results of his investigations of how light rays from celestial bodies are refracted when they enter the dense atmosphere surrounding the earth, under the title Ad vitellionem Paralipomena Quibus Astronomiae Pars Optica Traditur (Addendum to Vitellio on the Study of Optical Matters in Astronomy). Today, this book is considered the first modern work in optics. In the same year, a study of the new star, known today as the Kepler Supernova, is published.

Kepler begins his great struggle, also using Brahe's observation notes on Mars. This struggle will enable him to find three fundamental laws. Kepler first tries to calculate the orbit of Mars: For six years, he has worked hard, calling this exhausting process the battle against Mars. Its purpose is to show that the orbit of Mars is circular with the Copernican model and to prove this with Brahe's observation data. Kepler finds that Mars is in a circular orbit at only two locations, but Mars is in a circle at other locations. This discovery prompts him to use curves outside the circle. Observations show that the planet moves slowly, sometimes fast, as it goes around the sun. But the motion of the circle must be uniform, so the orbit is not a circle, and Kepler finds that the orbit must be elliptical. This is Kepler's first law. The planets, including our Earth, orbit in an ellipse with the Sun at one focus. With this law of Kepler, he says that planetary orbits, known as circles until then, are ellipses. This completely invalidates the deviations from the previous calculations with respect to the circle.

At this stage, the view of an elliptical orbit with the Sun at one of the two centers raises the question of how fast the planet is traveling in that orbit. As a result of calculations, Kepler finds that the planet moves fast when it is close to the Sun and slower when it is far away. Accordingly, the planet sweeps equal areas at equal times. Thus, Kepler finds his second law.

He published his book containing these two laws in 1609 under the name Astronomia Nova (New Astronomy). This book had a significant impact on the development of astronomy and astrophysics. Later, using Kepler's laws, the founder and father of modern physics, Isaac Newton, formulated the laws of motion of matter (Newton's Laws), as well as discovering the law of universal gravitation.

Previously, all telescopes were made of a concave lens and a convex lens, called the Galileo telescope. Kepler suggested that a better telescope could be made using two convex lenses instead of one concave and one convex lens, and in 1611 he built the first telescope of this kind, called the Kepler telescope. The Kepler telescope soon became popular when this type of telescope proved to be more suitable for astronomy than Galileo's telescopes.

After the death of Emperor Rudolf II, things take a turn for the worse and he moves to the city of Lunz with his family. At the beginning of 1611, Kepler's wife, Barbara, fell ill with Hungarian fever and began to have mental problems. Their three children contract smallpox. Susana and Ludwig recover from the illness, but Kepler's favorite 6-year-old son, Friedrich, dies, later losing his wife. In 1613, 41-year-old Kepler remarried 24-year-old Susanna Reuttinger, they had 7 children, one or two of whom survived.

In 1616, his 74-year-old mother was accused of witchcraft and arrested and tried for being burned in the fire. Kepler considers his mother to be slurred, meddlesome, angry, and constantly complaining about everything. With Kepler's efforts, his mother was saved from being cremated.

After these difficult years, Kepler finds the relationship between the periods and distances of the planets: the square of the periods of the planets and the cube of their distance from the Sun are proportional to each other. This is Kepler's third law. The ratio of the squares of the periods of the planets to the cubes of their distance from the Sun is equal.

In 1619 Kepler published Harmonices Mundi (Harmony of the World), which, in his own words, was the most important work of his life. The book, which consists of five parts, contains interesting information such as the relationship between the movements of the planets and the relationship between music and notes, as well as the third law, which is the main reason for writing the book.

Another interesting work by Kepler is Somnium (Dream). Kepler distributed this work, which he planned to print in 1611, among his friends. The work, which describes the journey to the moon, also includes Kepler's views on the geographical features of the moon, life in space, and other issues. Considered by some to be the first work of science fiction, The Dream was only published in 1634, after Kepler's death.

In 1627 he published the fundamental tables of the planets under the title Tabulae Rudophinae (Rudolf's Tables). Since Tycho started the study of Rudolf rulers, which determine the positions of the planets at different times with high precision, he decides to write the name of Tycho Brahe as the lead author of the book, even though he wrote the book entirely himself.

Dealing with astronomical rulers requires heavy arithmetic calculations, John Napier discovered the logarithm in 1616, but even the mathematicians of the time did not yet fully understand it. On top of that, Kepler publishes a study that shows how logarithm works and gives accurate results. He also makes use of logarithms while preparing Rudolf's Tables.

In 1630, Kepler went to Regensburg, Germany, to collect the money he was owed. He fell ill due to harsh conditions and cold, struggled with high fever and delirium, remained unconscious for a few days, and died on November 15, 1630. He is buried in St Peter's Protestant cemetery outside the Regensburg walls. However, this church was destroyed in the Thirty Years' War and no remains of the tomb remain.