Size according to Anaximander
The stars are wheel-shaped masses of air, full of fire, breathing out flames from pores in different partsÉ.  The sun has the highest position of all, the moon is next in order, and under it are the fixed stars and planetsÉ.  The circle of the sun is 28 times as large as the earth, like a chariot wheel, having a hollow center and this full of fire, shining in every part, and sending out fire through a narrow opening like the air from a flute.