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From the Astronomical Dictionary

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Nicholas Copernicus

Nicholas Copernicus (1473 - 1543) was an astronomer who wrote a book in which he claimed and gave evidence that all planets including the Earth orbit around the Sun (the heliocentric world view) instead of all (other) planets and the Sun orbiting around the Earth (the geocentric world view) like most people believed until then. Copernicus did still assume (like his predecessors) that all motions in the Universe were along circular orbits. Johan Kepler showed later that the orbits of the planets are far closer to ellipses than to circles. The work of Copernicus and Kepler caused most people to start believing in the heliocentric world view.