Biography of Johannes Kepler, Pioneering German Astronomer

Johannes Kepler with King Rudolf II
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Johannes Kepler (December 27, 1571–November 15, 1630) was a pioneering German astronomer, inventor, astrologer, and mathematician who is best known for the three laws of planetary motion now named for him. In addition, his experiments in the field of optics were instrumental in revolutionizing eyeglass and other lens-related technologies. Thanks to his innovative discoveries combined with his original and accurate methodology for recording and analyzing his own data as well as that of his contemporaries, Kepler is considered one of the most significant contributing minds of the 17th-century scientific revolution.

Johannes Kepler

  • Known For: Kepler was an inventor, astronomer, and mathematician who served as a central figure in the 17th-century scientific revolution.
  • Born: December 27, 1571 in Weil, Swabia, Germany 
  • Parents: Heinrich and Katharina Guldenmann Kepler
  • Died: November 15, 1630 in Regensburg, Bavaria, Germany
  • Education: Tübinger Stift, Eberhard Karls University of Tübingen
  • Published WorksMysterium Cosmographicum (The Sacred Mystery of the Cosmos), Astronomiae Pars Optica (The Optical Part of Astronomy), Astronomia Nova (New Astronomy), Dissertatio cum Nuncio Sidereo (Conversation with the Starry Messenger) Epitome Astronomiae Copernicanae (Epitome of Copernican Astronomy), Harmonices Mundi (Harmony of the Worlds)
  • Spouse(s): Barbara Müeller, Susan Reuttinger
  • Children: 11
  • Notable Quote: “I much prefer the sharpest criticism of a single intelligent man to the thoughtless approval of the masses.”

Early Life, Education, and Influences

Johannes Kepler was born on December 27, 1571, in Weil der Stadt, Württemburg, in the Holy Roman Empire. His family, once prominent, was relatively poor by the time he was born. Kepler's paternal grandfather Sebald Kepler, a respected craftsman, had served as mayor of the city. His maternal grandfather, innkeeper Melchior Guldenmann, was mayor of the nearby village Eltingen. Kepler's mother Katharina was an herbalist who helped run the family hostelry. His father Heinrich served as a mercenary soldier.

Kepler's gift for mathematics and interest in the stars became evident at an early age. He was a sickly child, and while he survived a bout of smallpox, he was left with weak vision and damage to his hands. His poor eyesight did not hinder his studies, however. In 1576, Kepler began attending the Latin school in Leonberg. He witnessed both the passing of The Great Comet of 1577 and a lunar eclipse in the same year, which were thought to have been inspirational in his later studies.

In 1584, he enrolled at the Protestant seminary at Adelberg, with the goal of becoming a minister. In 1589, after obtaining a scholarship, he matriculated to the Protestant University of Tübingen. In addition to his theological studies, Kepler read widely. While at university, he learned of the astronomer Copernicus and became a devotee of his system.

Career, Religion, and Marriage

After graduation, Kepler obtained a position teaching mathematics in Graz, Austria, at the Protestant seminary. He was also appointed district mathematician and calendar maker. It was in Graz that he penned his defense of the Copernican system "Mysterium Cosmographicum" in 1597. Kepler married a wealthy 23-year-old twice-widowed heiress named Barbara Müeller that same year. Kepler and his wife began their family but their first two children died in infancy.

As a Lutheran, Kepler followed the Augsburg Confession. However, he did not accept the presence of Jesus Christ in the sacrament of Holy Communion and refused to sign the Formula of Accord. As a result, Kepler was exiled from the Lutheran Church (his subsequent refusal to convert to Catholicism left him at odds with both sides when the Thirty Years' War broke out in 1618) and was obliged to leave Graz.

In 1600, Kepler moved to Prague, where he had been hired by Danish astronomer Tycho Brahe—who held the title of Imperial Mathematician to Emperor Rudolph II. Brahe tasked Kepler with analyzing planetary observations and writing arguments to refute Brahe's rivals. Analysis of Brahe's data showed that the orbit of Mars was an ellipse rather than the perfect circle that was always held to be ideal. When Brahe died in 1601, Kepler took over Brahe's title and position.

In 1602, Kepler's daughter Susanna was born, followed by sons Friedrich in 1604 and Ludwig in 1607. In 1609, Kepler published "Astronomia Nova," which contained the two laws of planetary motion that now bear his name. The book also detailed the scientific methodology and thought processes he'd used to arrive at his conclusions. "It is the first published account wherein a scientist documents how he has coped with the multitude of imperfect data to forge a theory of surpassing accuracy," he wrote.

Mid-Career, Remarriage, and War

When Emperor Rudolph abdicated to his brother Matthias in 1611, Kepler's position became increasingly precarious due to his religious and political beliefs. Kepler's wife Barbara came down with Hungarian spotted fever that same year. Both Barbara and Kepler's son Friedrich (who'd contracted smallpox) succumbed to their illnesses in 1612. After their deaths, Kepler accepted a position as district mathematician for the city of Linz (a post he retained until 1626) and was remarried in 1613 to Susan Reuttinger. His second marriage was reported to be happier than his first, although three of the couple's six children died in childhood.

At the opening of the Thirty Years' War in 1618, Kepler’s tenure in Linz was further imperiled. As a court official, he was exempt from the decree banishing Protestants from the district but he did not escape persecution. In 1619, Kepler published "Harmonices Mundi" in which he laid out his "third law." In 1620, Kepler's mother was accused of witchcraft and put on trial. Kepler was obliged to return to Württemburg to defend her against the charges. The following year saw the publication of his seven-volume "Epitome Astronomiae" in 1621, an influential work that discussed heliocentric astronomy in a systematic way.

During this time, he also completed the "Tabulae Rudolphinae" ("Rudolphine Tables") begun by Brahe, adding his own innovations that included calculations arrived at by the use of logarithms. Unfortunately, when a peasant rebellion erupted in Linz, a fire destroyed much of the original printed edition.

Later Years and Death

As the war dragged on, Kepler's house was requisitioned as a garrison for soldiers. He and his family departed Linz in 1626. By the time the "Tabulae Rudolphinae" was eventually published in Ulm in 1627, Kepler was unemployed and was owed a great deal of unpaid salary from his years as Imperial Mathematician. After efforts to obtain numerous court appointments failed, Kepler returned to Prague in an attempt to recoup some of his financial losses from the royal treasury.

Kepler died in Regensburg, Bavaria, in 1630. His gravesite was lost when the churchyard in which he was buried was destroyed at some time during the Thirty Years' War.


More than an astronomer, Johannes Kepler's legacy spans a number of fields and encompasses an impressive number of scientific firsts. Keplar both discovered the universal laws of planetary motion and explained them correctly. He was the first to correctly explain how the moon creates the tide (which Galileo disputed) and the first to suggest that the Sun rotates around its axis. In addition, he calculated the now commonly accepted birth year for Jesus Christ and coined the word "satellite."

Kepler's book "Astronomia Pars Optica" is the foundation of the science of modern optics. Not only was he the first to define vision as a process of refraction within the eye, as well as explain the process depth perception, he was also first to explain the principles of the telescope and describe the properties of total internal reflection. His revolutionary designs for eyeglasses—for both nearsightedness and farsightedness—literally changed the way in which people with vision impairments see the world.


  • “Johannes Kepler: His Life, His Laws and Times." NASA.
  • Casper, Max. "Kepler." Collier Books, 1959. Reprint, Dover Publications, 1993.
  • Voelkel, James R. "Johannes Kepler and the New Astronomy." Oxford University Press, 1999.
  • Kepler, Johannes, and William Halsted Donahue. "Johannes Kepler: New Astronomy." Cambridge University Press, 1992.