Astronomer Johannes Kepler was born
On this day · 27 December 1571
Born on this day in 1571, Kepler replaced ancient perfect circles with ellipses and gave planetary motion its mathematical laws.
On December 27, 1571, Johannes Kepler was born in Weil der Stadt, in what is now Germany. He would become the mathematician who finally cracked the geometry of the heavens.
Working from the meticulous observations of the Danish astronomer Tycho Brahe, Kepler abandoned a belief that had held since antiquity: that planets must travel in perfect circles. Instead, he showed that the orbit of Mars — and, by extension, every planet — is an ellipse, with the Sun at one focus. This became Kepler’s First Law.
His Second Law held that a line from a planet to the Sun sweeps out equal areas in equal times, so planets move faster when nearer the Sun. His Third Law, published in 1619, tied the square of a planet’s orbital period to the cube of its average distance.
Kepler is credited with inventing celestial physics, treating the Sun as the force driving the planets.
Those three laws later gave Newton the foothold for universal gravitation.
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