- Under the Ptolemaic geocentric worldview, the Earth is used as the central position from which planetary and celestial movements are measured. This perspective was able to provide a good, workable, astronomical model, which suited the practical requirements of early and medieval societies, whilst also conforming to Aristotelian philosophical principles
Each planet moves within its own sphere, its position in the scheme reflecting upon its apparent speed of motion and its astrological meaning. Saturn's sphere is the highest and slowest, the Moon's is the lowest and quickest. The area between the Earth and Moon was described as the sub-lunar sphere, which was filled with corruption and change. For a good, concise account of this philosophy see David Plant's description at www.skyscript.co.uk/sublunar.html
The geocentric cosmos by Peter Apian, Cosmographicus Liber (1539), showing the 'impure' sublunar sphere and the Chaldean order of the planetary spheres descending towards the Earth.
© Deborah Houlding, 16/02/10