In astronomy, heliocentrism is the theory that the Sun is at the center of the Milky Way. The word came from the Greek (ήλιος Helios = sun and κέντρον kentron = center). Historically, heliocentrism was opposite to geocentrism, which located the earth at the center. (The distinction between the Solar System and the Universe was not clear until modern times, but very significant relative to the controversy over cosmology and religion). The Greek Aristarchus of Samos, in the 3rd century BC, was the first known person to wonder that the Earth revolves around a stationary sun. It was not until 1,800 years later, though, in the 16th century, that the Polish mathematician and astronomer Copernicus obtainable a fully predictive mathematical model of a heliocentric system, which was later, elaborated and prolonged by Johannes Kepler.
