Caption: The image shows Ptolemy's (c.100--c.170 CE) physical model for the orbit of Venus and the superior planets (Mars, Jupiter, Saturn) as understood by Georg von Peuerbach (1423--1461). This physical model can be called Ptolemaic physical model of the Solar System (see Wikipedia: Ptolemy: Astronomy).

Features:

1. Ptolemy at some time after completing the Almagest (which gives Ptolemaic system largely as a calculation tool for planetary ephemerides) created the Ptolemaic physical model in his book Planetary Hypotheses (c.150).

   The Ptolemaic physical model is a hybrid of the Ptolemaic system (all based on epicycle theory) and Aristotelian cosmology.

2. The Ptolemaic physical model fits the deferents with epicycles into the celestial spheres of Aristotelian cosmology.

3. In the image, mundi is Earth (which is the center of the universe in geocentric solar system model), deferentis is the center of the deferents (which is the white band), and aequantis equant.

4. The actual epicycle is represented by the 3 small circles and the planet (NOT shown) is carried around on the epicycle which is carried around on the deferent at a constant angular velocity as viewed from the equant.

5. From the Ptolemaic physical model (which requires more explication than we have given here), Ptolemy was able to deduce the sizes of the orbits and of the celestial sphere of the stars.

6. Of course, his values are very wrong since the Ptolemaic physical model is wrong.

7. The Ptolemaic physical model was rejected by strict Aristotelians because it is NOT pure Aristotelian cosmology and perhaps other reasons.

   Those who were just interested in positional astronomy---for, among other things, preparing ephemerides and doing astrology---had NO interested in it.

   Only those interested in the physical cosmology had an interest in it. But in the historical record, they do NOT seem to have had much interest.

8. The Ptolemaic physical model is an interesting example of doing science for the history of science, but NOT very important in the history of science.

9. The Ptolemaic physical model illustrates Ptolemy's genius and its limitations.

   He tried to deduce real things (i.e., Solar-System distances) from his physics---which is good---but his physics was very bad---which is bad---he was barking up the wrong tree.