Detail of the Earth at the centre of the armillary sphere. Made by Girolamo della Volpaia (c 1530-1614) of Florence, Italy, this bras armillary sphere encloses a manuscript terrestrial globe. A finely engraved band with the star patterns of the Zodiac encircles the instrument. The armillary sphere is a demonstration device used 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 can act as a model 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.
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