‘Astronomy in the Middle Ages’ examines how the ideas of Ptolemy and antiquity were preserved and transmitted, initially by the scholars of Islam. They built a number of observatories and also developed the astrolabe. It was the introduction of the astrolabe into the West at the turn of the Millennium that revived an interest in astronomy in the West. At the same time the writings of antiquity were recovered and translated and with the introduction of the printing press their ideas were more widely disseminated. Ptolemy's ideas in the Almagest were finally surpassed when Nicolaus Copernicus wrote his De revolutionibus, arguing that the Earth orbited the Sun.