A German mathematician and astronomer who lived from 1571 to 1630. Kepler was the first person to model planetary orbits as ellipses instead of circles. He tested his theory of elliptical orbits using Danish astronomer Tycho Brahe’s observations of planetary motion in the sky. In 1609, he published his findings in a book called Astronomia nova (The New Astronomy), in which he summarized planetary motion with three laws.
