________________________________________________________________________________________________________________________________________________Aristarchus was a Greek astronomer who lived in the 200's BC. He was the first astronomer to state that the earth revolved around the sun, and not the other way around. This fact came to us not through his writing, but by a quotation used by Archimedes.
Copernicus was never a professional Astronomer, but came to the same conclusion os Aristarchus. Copernicus' theory of heliocentric, or sun centered, cosmology states that the Sun (not the Earth as was normally viewed) is at rest in the center of the Universe, with the other heavenly bodies (planets and stars) revolving around it in circular orbits. A full account of the theory titled, On the Revolutions of the Heavenly Spheres (De Revolutionibus Orbium Coelestium) was published in 1543, very near the end of Copernicus's life.
Copernicus' heliocentric system was considered implausible by the vast majority of his contemporaries, and by most astronomers and natural philosophers until the middle of the seventeenth century. Its notable defenders included Johannes Kepler (1571 -1630) and Galileo Galilei (1564 - 1642). Strong theoretical underpinning for the Copernican theory was finally provided by Sir Isaac Newton's theory of universal gravitation (1687).
