Bras armillary sphere, 1552.
© Science Museum / Science & Society Picture Library
Made by Caspar Vopel (1511-1561) in Cologne, Germany, this bras armillary sphere is mounted on a turned wooden stand. A broad band, finely engraved with the star patterns of the Zodiac encircles the instrument. The armillary sphere is a demonstration device to explain the movements of the Sun, Moon, stars and planets acros the sky. Its interlocking rings can be used to teach astronomical principles in the same manner as a celestial globe, or it can act as a model of the universe. Based on the premise of an Earth-centred universe, the armillary sphere had to be modified in the 17th century in order to teach the new theory that the Earth orbits the Sun.