Johannes Kepler (27 December 1571 – 15 November 1630) was a German mathematician, astronomer, and natural philosopher who fundamentally transformed humanity’s understanding of the cosmos. Born in Weil der Stadt, Germany, to a soldier father and an herbalist mother who was later accused of witchcraft, Kepler studied at the University of Tübingen under Michael Maestlin, who taught him the Copernican heliocentric system.
In 1596, Kepler published Mysterium Cosmographicum (The Cosmographic Mystery), the first published defense of Copernicus’s suncentered model. After being forced out of his teaching position in Graz due to his Lutheran faith, he moved to Prague in 1600 to work for the renowned astronomer Tycho Brahe. When Tycho died suddenly in 1601, Kepler succeeded him as imperial mathematician to Holy Roman Emperor Rudolf II.
Kepler’s greatest achievement was his three laws of planetary motion: that planets move in elliptical orbits with the sun at one focus (1609); that a line connecting a planet to the sun sweeps equal areas in equal times; and that the square of a planet’s orbital period is proportional to the cube of its mean distance from the sun (1619). These laws, published in Astronomia Nova (1609) and Harmonices Mundi (1619), laid the foundation for Newton’s law of universal gravitation.
Called the “founder of celestial mechanics,” Kepler was the first to identify natural laws in the modern sense. His fusion of physics and astronomy created modern astronomical science, demonstrating that the same physical principles governing motion on Earth apply throughout the universe—a revolutionary insight with profound implications for understanding humanity’s place in the cosmos.