Caption: A cartoon of the Eudoxon model for explaining the motion of the Sun around the Earth.

Features:

1. The Eudoxon models of planetary motion were invented by Eudoxus of Cnidus (410 or 408--355 or 347 BCE).

2. At the quantitative level, Eudoxon models did NOT succeed in explaining planetary motion. Even qualitatively, their success is limited. But you have to begin somewhere.

3. They are GEOCENTRIC, FINITE cosmological models.

   We do NOT know to what extent Eudoxus considered the Eudoxon models to be physically real.

4. In the Eudoxon models, the fixed stars are pasted on celestial sphere of the stars thought of as a real surface with surrounding an unmoving spherical Earth at the center.

5. The celestial sphere of the stars rotates around the Earth once per day.

6. There are compounded celestial spheres to account for the motions of the planets: (which include the Sun and Moon in this context).

7. The cartoon illustrates the Sun sphere which carries the Sun.

   It rotates once per year relative to the celestial sphere of the stars.

   The compounded motion of Sun sphere and celestial sphere of the stars qualitatively accounts for the motion of the Sun on the sky.

8. Similar, but more complicated, Eudoxon models (with rotation rates fitted to the observations) account qualitatively for the motions of the other planets.

9. A key feature of the Eudoxon models is that the planets (including the Sun and Moon) are never change their distances from the Earth.

   This is also true in Aristotelian cosmology which incorporates Eudoxon models.

10. The Eudoxon models were the first ones to qualitatively explain the more difficult celestial motions in terms of 3-dimensional geometric structures. The more complex Eudoxon models do qualitatively give apparent retrograde motions for the planets.