Born in: Weil der Stadt, near Stuttgart, Germany
Career: Astronomy, Astrology, Mathematics and Natural Philosophy
Death: November 15, 1630
Johannes Kepler played a vital role in the 17th century astronomical revolution. He was a German mathematician, astronomer and astrologer and is well known for his eponymous laws of planetary motion. These were codified by later astronomers, based on his works Astronomia Nova, Harmonices Mundi, and Epitome of Copernican Astronomy. Kepler's laws provided foundations for Isaac Newton's theory of Universal Gravitation. He also did elementary work in the field of optics, especially in inventing an improved version of the refracting telescope, the Keplerian Telescope. Kepler even helped to legitimize the telescopic discoveries of Galileo Galilei.
Kepler was born on 27th December 1571, at the Imperial Free City of Weil der Stadt, which now lies in the German state of Baden-Württemberg. His father, Heinrich Kepler, worked as a mercenary and left the family when Johannes was five years old. It is believed that he died in the Eighty Years' War in Netherlands. His mother Katharina Guldenmann was an inn-keeper's daughter and worked as a healer and herbalist. She was later tried for witchcraft. Kepler was born prematurely and was a weak and sickly child.
Kepler was a brilliant child since the very beginning. He often impressed travelers at his grandfather's inn, with his phenomenal mathematical faculty. He was introduced to astronomy at an early age and developed affinity towards it. At the tender age of six, he observed the Great Comet of 1577. At age nine, he observed the lunar eclipse of 1580. Unfortunately, he suffered from smallpox in childhood, which left him with weak vision and crippled hands, limiting his ability in the observational aspects of astronomy.
In 1589, Kepler attended the University of Tübingen as a theology student, after passing grammar school, Latin school & lower & higher seminary in Württemberg state-run Protestant education system. Later, he studied philosophy under Vitus Müller. Kepler proved to be an extraordinary mathematician and a reputed astrologer, casting horoscopes for fellow students. He learned both Ptolemaic system and Copernican system of planetary motion and became a Copernican. Towards the end of his studies, Kepler was recommended as a teacher of mathematics and astronomy at the Protestant school in Graz, Austria (later University of Graz), which he accepted in April 1594.
In 1959, Kepler met 23 year old Barbara Muller, who was a two-time widow, with a daughter, and began courting her. Apart from the fortunes inherited from her husbands, Muller was the daughter of a successful mill owner. Owing to Kepler’s poverty, Muller’s father opposed the marriage. However, the couple finally got married on April 27, 1597. In the first years of their marriage, Keplers had two children, Heinrich and Susanna, both of whom died in infancy. In 1602, they had a daughter Susanna, in 1604, a son Friedrich and in 1607, another son Ludwig.
In 1611, Barbara suffered from Hungarian spotted fever and while she was recovering, all the three children fell sick of small pox. In effect, their son, Friedrich died at the age of six. This was followed by Barbara’s death. After this, Kepler married the twenty-four-year-old Susanna Reuttinger, in 1613. The first three children of this alliance, Margareta Regina, Katharina, and Sebald died in childhood. However, three survived into adulthood, namely Cordula, Fridmar and Hildebert. Kepler died on November 15, 1630, and was buried in Regensburg.
- The first significant astronomical work of Kepler was Mysterium Cosmographicum (The Cosmographic Mystery). It was the first published defense of the Copernican system. Mysterium was published in 1596 and Kepler sent its copies to prominent astronomers and patrons early in 1597. Though it was not widely read, it established Kepler’s reputation as a highly skilled astronomer.
- Kepler published an expanded second edition of Mysterium in 1621. It included detailing in footnotes, the corrections and improvements he had achieved in the 25 years since its first publication.
- On 1st January 1604, Kepler published Astronomiae Pars Optica (The Optical Part of Astronomy). It described the inverse-square law governing the intensity of light, reflection by flat and curved mirrors, principles of pinhole cameras, as well as the astronomical implications of optics such as parallax and the apparent sizes of heavenly bodies. It is regarded as the foundation of modern optics.
- In October 1604, a bright new evening star (SN 1604) was seen. Two years later, Kepler described the new star in his ‘De Stella Nova’. It addressed the star's astronomical properties.
- An extended research resulted in Astronomia nova (A New Astronomy) - including the first two laws of planetary motion. It was published in 1609.
- In 1611, Kepler published Dioptrice, wherein he explained the theoretical basis of double-convex converging lenses and double-concave diverging lenses, the concepts of real vs. virtual images, upright vs. inverted images, and the effects of focal length on magnification and reduction. He also described an improved telescope, now known as the astronomical or Keplerian telescope.
- In 1615, he completed the first of three volumes of Epitome astronomia Copernicanae (Epitome of Copernican Astronomy). The first volume (books I-III) was printed in 1617, the second (book IV) in 1620 and the third (books V-VII) in 1621. It contained all the three laws of planetary motion and attempted to explain heavenly motions through physical causes thereby becoming Kepler's most influential work.
- In 1623, Kepler completed the Rudolphine Tables, which were printed in 1627.
- In 1611, he published Strena Seu de Nive Sexangula (A New Year's Gift of Hexagonal Snow) in which he investigated the hexagonal symmetry of snowflakes and extended the discussion into a hypothetical atomistic physical basis for the symmetry posed. This later came to be known as the Kepler conjecture, a statement about the most efficient arrangement for packing spheres.
- In 1619, Harmonices Mundi ("Harmony of the Worlds") was published, which was based on ‘harmonic theory’. With this, he attempted to explain the proportions of the natural world, particularly the astronomical and astrological aspects, in terms of music.
Johannes Kepler could be seen as one of the motifs of one of the most famous silver collector's coins: the 10-euro Johannes Kepler silver coin, minted in September 10, 2002. The reverse side of the coin carries a portrait of Kepler, in front of which, the model of nested spheres and polyhedra from Mysterium Cosmographicum is engraved.