Biography of Johannes Kepler

The Inventor Who Changed Astronomy

Public Domain


Johannes Kepler (born December 27, 1571) was a German astronomer and mathematician in 17th century Europe who discovered the laws of planetary motion. His success was also due to his inventions that allowed him and others to make new discoveries as well as analyze and record them. He also created log books to calculate planetary positions and experimented with optics, including making eyeglasses and a convex eyepiece.

Live and Work of Johannes Kepler

Johannes Kepler was born on December 27, 1571, in Weil der Stadt, Württemburg, in the Holy Roman Empire. He was a sickly child and had weak vision due to a bout of smallpox. His family had been prominent, but by the time he was born, they were relatively poor. He had a gift for mathematics from a young age and got a scholarship to the University of Tübingen, planning to become a minister.

He learned of Copernicus in the university and became a devotee to that system. His first position out of the university was to teach mathematics and astronomy in Graz. He wrote a defense of the Copernican system called the "Mysterium Cosmographicum" in 1696 in Graz.

As a Lutheran, he followed the Augsburg Confession. However, he did not believe in the real presence of Christ in the sacrament of Holy Communion and he refused to sign the Formula of Accord. As a result, he was excluded from Lutheran Church and didn't want to convert to Catholicism, leaving him at odds with both sides of the Thirty-Years War. He had to leave Graz.

Kepler moved to Prague in 1600, where he was hired by Danish astronomer Tycho Brahe to analyze planetary observations and write arguments against Brahe's rivals. When Brahe died in 1601, Kepler took over his title and work as the imperial mathematician to Emperor Rudolph II.

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. In 1609, he published "Astronomia Nova," which contained his two laws of planetary motion and now bear his name. Beyond that, he showed his work and thought processes by outlining the scientific method he used to arrive at his conclusions. For example, he wrote "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." (O. Gingerich in forward to Johannes Kepler New Astronomy translated by W. Donahue, Cambridge Univ Press, 1992).

When Emperor Rudolph abdicated to his brother Matthias in 1611, the Kepler family hit a rough patch. Being nominally Lutheran, he was obliged to move from Prague, but his Calvinist beliefs made him unwelcome in Lutheran areas. His wife died from Hungarian spotted fever and his son died of smallpox. He was allowed to move to Linz and remained the imperial mathematician under Matthias. He remarried happily, although three of the six children from this marriage died in childhood. Later, Kepler had to return to Württemburg to defend his mother against charges of witchcraft. In 1619, he published "Harmonices Mundi" wherein he describes his "third law."

Kepler published the seven-volume "Epitome Astronomiae" in 1621. This influential work discussed all of heliocentric astronomy in a systematic way. He completed the Rudolphine Tables that were started by Brahe. His innovations in this book included developing calculations using logarithms. He developed perpetual tables that could predict planetary positions, with their validity proven after his death during solar transits of Mercury and Venus.

Kepler died in Regensburg in 1630, though his grave site was lost when the churchyard was destroyed in the Thirty Years War.

A List of Johannes Kepler's Firsts

Source: Kepler Mission, NASA

  • Discovered the universal laws of planetary motion and explained them correctly.
  • Founder of modern optics due to his book, "Astronomia Pars Optica."
  • Investigated forming pictures with a pinhole camera.
  • Explained vision as a process of refraction within the eye.
  • Designed eyeglasses for nearsightedness and farsightedness.
  • Explained depth perception by the use of two eyes.
  • In his book "Dioptrice," he was the first to describe describe real, virtual, upright and inverted images and magnification.
  • Became the first to explain the principles of the telescope.
  • First to discover and describe the properties of total internal reflection.
  • His book "Stereometrica Doliorum" formed the basis of integral calculus.
  • Explained how the moon creates the tide (which an errant Galileo disputed).
  • Became father of astrometry by using the principles he developed for depth perception to attempt to use stellar parallax to measure the distance to the stars. 
  • First to suggest that the Sun rotates about its axis in "Astronomia Nova."
  • Derived a birth year of Christ that is now commonly accepted.
  • First to derive logarithms purely based on mathematics independent of Napier's tables published in 1614.​
  • Coined the word "satellite" in his pamphlet "Narratio de Observatis a se quatuor Iovis sattelitibus erronibus"