Title page from 'Astronomia nova' (New astronomy) by German astronomer Johannes Kepler (1571-1630) published in Heidelberg in 1609. Modern astronomy started with the publication here of Kepler's first two laws of planetary motion: 1. The orbit of a planet is an ellipse of which the sun is in one focus; 2. In describing its orbit, the radius vector of a planet traverses equal areas in equal time. Kepler became a follower of Copernicus whilst studying theology. He later worked with Tycho Brahe in Prague where he worked out the orbit of Mars. This led him to discover the laws of planetary motion. Kepler was also influential in the evolution of infinitesimal calculus.
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