Nor do the planets revolve round the sun – as every schoolboy believes that Copernicus taught. The planets move on epicycles of epicycles, centred not on the sun, but on the centre of the earth’s orbit. There are thus two ‘royal thrones’: the sun, and that imaginary point in space around which the earth moves. The year, that is, the duration of the earth’s complete revolution round the sun, has a decisive influence on the motions of all other planets. In short, the earth appears equal in importance in governing the solar system to the sun itself, and in fact nearly as important as in the
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