Nicolaus Copernicus 1473_1543 observing a lunar eclipse in Rome in 1500, coloured historical artwork. Copernicus was a Polish astronomer who began the revolution that overthrew more than 1000 years of astronomical thought. Since the time of Ptolemy in the second century AD, the Earth had been considered to be the immovable centre of the universe. From 1512, Copernicus developed his heliocentric theory, where the Earth was one of several planets moving around the Sun. Copernicus feared persecution by the Roman Catholic Church, and delayed publication of his book, The Revolution of the Heavenly Spheres, until the year he died. Engraving from the 1875 edition of Vies des Savants Illustres.