Caption: The Philolaic system (later 5th century BCE) of the Pythagorean Philolaus (c.470--c.385 BCE).

Features:

1. The Philolaic system is the first planetary system model we know of for Solar System.

   By "planetary system model", we mean that it tried to account for planetary motions through 3-dimensional outer space.

2. Remarkably, the Philolaic system is neither a geocentric solar system nor a heliocentric solar system.

   The Philolaic system is center on a hypothetical Central Fire---it is Central-Fire-ocentric.

3. All the then-known Solar System bodies (including the Earth) orbit the Central Fire.

   But we never observe the Central Fire since our side of the Earth always faces away from it as the Earth orbits it.

4. The Earth's shape in the Philolaic system is NOT specified (Wikipedia: Pythagorean astronomial system: Earth)---spherical Earth or flat Earth?

   If flat Earth, the Earth may have been thought of a disk shaped.

5. There is also a Philolaic-system Counter-Earth orbiting the Central Fire, but we never observe it since it orbits just so that it is always at superior conjunction relative to the Central Fire. See also Wikipedia: Counter-Earth.

6. Later Greek astronomers would consider the fixed stars as pasted on a celestial sphere of the stars beyond the planetary system. This may NOT be true of the Philolaic system.

7. The Philolaic system only very partially and qualitatively corresponds to astronomical observations insofar as we understand it.

   There is NO evidence that anyone every tried to make it a quantitative model of mathematical astronomy.

8. The Philolaic system may have been invented largely to satisfy philosophic concerns and actually contains elements of fantasy or as we would now say scifi---the Moon is inhabited by Selenites 15 times stronger than Earthlings (see David J. Furley 1987, The Greek Cosmologists, p. 57--58).