Editing Celestial spheres (section)

===Early ideas of spheres and circles===

In [[Ancient Greece|Greek antiquity]] the ideas of celestial spheres and rings first appeared in the cosmology of [[Anaximander]] in the early 6th century BC.<ref>See chapter 4 of Heath's ''Aristarchus of Samos'' 1913/97 Oxford University Press/Sandpiper Books Ltd; see p. 11 of Popper's ''The World of Parmenides'' Routledge 1998</ref> In his cosmology both the Sun and Moon are circular open vents in tubular rings of fire enclosed in tubes of condensed air; these rings constitute the rims of rotating chariot-like wheels pivoting on the Earth at their centre. The fixed stars are also open vents in such wheel rims, but there are so many such wheels for the stars that their contiguous rims all together form a continuous spherical shell encompassing the Earth. All these wheel rims had originally been formed out of an original [[sphere of fire]] wholly encompassing the Earth, which had disintegrated into many individual rings.<ref>Heath  ''ibid'' pp26–8</ref> Hence, in Anaximander's [[cosmogony]], in the beginning was the sphere, out of which celestial rings were formed, from some of which the stellar sphere was in turn composed. As viewed from the Earth, the ring of the Sun was highest, that of the Moon was lower, and the sphere of the stars was lowest.

Following Anaximander, his pupil [[Anaximenes of Miletus|Anaximenes]] ({{Circa|586/585 BCE|526/525 BCE}}) held that the stars, Sun, Moon, and planets are all made of fire. But whilst the stars are fastened on a revolving crystal sphere like nails or studs, the Sun, Moon, and planets, and also the Earth, all just ride on air like leaves because of their breadth.<ref>See chapter 5 of Heath’s 1913 ''Aristarchus of Samos''</ref> And whilst the fixed stars are carried around in a complete circle by the stellar sphere, the Sun, Moon and planets do not revolve under the Earth between setting and rising again like the stars do, but rather on setting they go laterally around the Earth like a cap turning halfway around the head until they rise again. And unlike Anaximander, he relegated the fixed stars to the region most distant from the Earth. The most enduring feature of Anaximenes' cosmos was its conception of the stars being fixed on a crystal sphere as in a rigid frame, which became a fundamental principle of cosmology down to Copernicus and Kepler.

After Anaximenes, [[Pythagoras]], [[Xenophanes]] and [[Parmenides]] all held that the universe was spherical.<ref>For Xenophanes' and Parmenides' spherist cosmologies see Heath ''ibid'' chapter 7 and chapter 9 respectively, and Popper ''ibid'' Essays 2 & 3.</ref> And much later in the fourth century BC Plato's ''[[Timaeus (dialogue)|Timaeus]]'' proposed that the body of the cosmos was made in the most perfect and uniform shape, that of a sphere containing the fixed stars.<ref>F. M. Cornford, ''Plato's Cosmology: The Timaeus of Plato'', pp. 54–7</ref> But it posited that the planets were spherical bodies set in rotating bands or rings rather than wheel rims as in Anaximander's cosmology.