born in modern Turkey. He developed a model of planetary motion in which the Sun, Moon, and planets were carried around the Earth on a series of 27 Earth-centred spheres, with axes at different angles and rotating at different speeds. This theory of ‘heavenly spheres’, as modified first by Callippus and ultimately by Ptolemy, remained the orthodox view of the Universe for two thousand years. Eudoxus is also reputed to have introduced the constellation system from Egypt.