Portrait of Polish astronomer Nicolaus Copernicus (14731543). Copernicus recognised that the cosmology proposed by Ptolemy over 1000 years before was inadequate to explain the motion of the celestial bodies. He developed in full mathematical detail a new cosmology in which the Sun was at the centre of the Universe with the planets & stars orbiting it in circular orbits (as illustrated in the panel beneath the portrait). Copernicus hesitated to reveal his ideas, but they were published in 1543 in his book De Revolutionibus Orbium Celestium (On the Revolution of the Heavenly Spheres). This colour engraving was made in the 19th century.