The sun, moon and planets were very different. They stayed in the heavens, and hence were presumably kept in place by the Gods. This did not stop people from trying to understand the motion of the planets in terms of familiar concepts. For example, the ancient Greeks knew of seven heavenly bodies (the sun, moon, mars, jupiter, venus, mercury and saturn)that they thought orbited the Earth. They thought that these heavenly bodies each moved in circles circumscribed on seven different spheres that had the Earth at their center. Their main reason for believing this was that they viewed the circle and sphere as the most perfect geometrical shapes (being the most symmetrical) and assumed that the motion of the heavenly bodies could be based on nothing less than perfection. In an attempt to synthesize the motion of the planets with more Earthly, but no less divine, concepts, the Greeks associated each of the seven spheres with one of the seven notes of the musical scale. This association of music with astronomy was called the Harmony of the Spheres, and formed the basis for many ancient astronomers' understanding of the Heavens.