Sixteenth century engraving of Claudius Ptolemy (AD c100-170), an Egyptian, or possibly Greek, astronomer, using a quadrant and being guided by the muse Astronomy. The Ptolemaic system held that the Earth was at the centre of the Universe and that the Sun and planets revolved about it. This view dominated astronomical thinking until it was unseated by Copernicus in 1543 in his work De Revolutionibus, in which he showed that the Earth revolved around the Sun. The engraving is from Margarita Philosophica by Gregor Reisch, published in 1508.