Armillary sphere. 18th century engraving of an armillary sphere, here termed an ‘artificial sphere’. This is a model of the celestial sphere, with the Earth at its centre and various loops depicting the equator, tropics, polar circles and the plane of the ecliptic. Once correctly set up, the armillary sphere could be used to show the rotation of the Earth, or the apparent rotation of the stars, and to predict sunrise and sunset times for any position on the Earth at any time in the future. This illustration first appeared in the Gentleman’s Magazine in 1748.