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- In Aristotle's (384 - 322 BC) conception of the universe, the Earth was the
- fixed centre, and visible movements of the heavenly bodies including the Sun
- were caused by the smooth rotations of 56 concentric crystal spheres around the
- Earth. Furthest out was the sphere of fixed stars. The friction of the spheres
- created music, which only the sharpest ears could hear.
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- The Earth was the centre of the universe because it was composed of heavy
- substances, which tend towards the centre. Aristotle divided the universe into
- sublunar and superlunar worlds. Perfect circular motion was characteristic of
- superlunar bodies. In Aristotle's conception comets were sublunar; that is, they
- were atmospheric phenomena.
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- Aristotle and his teacher, Plato. Painting by Rafaello.
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