The heavens move like a sphere:

• Ptolemy claims the heavens are spherical. What basic set of observations motivates this description? Are these observations accessible to the common person?

• In what two distinct ways does the spherical hypothesis bring unity to the account of observations of the heavens?

• Why is it important, for one description of the heavens to simultaneously explain the observations of people located at different times? At different locations?

• Why is it ridiculous, “that the same stars are already ignited or extinguished for some observers while they are not yet for others?”

• Why is it “utterly obvious that the very same stars that rise and set in certain regions of the earth neither rise nor set in other regions?” How does Ptolemy know this?

The earth too, taken as a whole, is sensibly spherical:

• In his arguments for a spherical earth, Ptolemy uses the timing of rising and setting of stars, and lunar eclipses. What exact information is he referring to, and how might he have gotten it?

• What does the reader have to do, in order to follow Ptolemy’s geometrical arguments? Are his arguments rigorous? Are they obvious, or do they require a certain level of intelligence on the reader’s part?

• To seal his argument, Ptolemy invokes the image of a mountain seen from a sailing vessel, as it rises out of the sea. Why is this useful?

The earth has the ratio of a point to the heavens:

• Does Ptolemy know how big the heavens are? The earth?

• Once again Ptolemy wants to unify the accounts of all observations. How does the earth’s having the “ratio of a point to the heavens” accomplish this unification? What would happen if the earth was not like a point, compared to the heavens?

Neither does the earth have any motion from place to place:

• Why was it so difficult for Ptolemy to accept that the earth might be moving?

• In light of the arguments in the previous section, what is the obvious flaw in Ptolemy’s argument, that the earth is immobile? 

• What does Ptolemy mean by “proper, natural motion?” Is this concept based on observation? Does it have explanatory and predictive power?

• How does the uniqueness of the universe limit any scientific study of it? Are there other areas of study, scientific or otherwise, that have this “problem?” Is cosmology a science?

• Does the concept of proper and natural motion be applied to the earth?

• At the same time Ptolemy describes the earth as having very little mass, and as having great mass. Why does he do this? Does it make sense as part of the logical argument for earth’s immobility?

• Ptolemy is reluctant to accept the idea that the earth might be rotating. Are his arguments based solely on common sense and observation, or does he show a theoretical bias? What concepts does he lack, that would make this possibility more plausible?

The article as a whole:

• What kind of arguments does Ptolemy use to prove his case? Are they abstract and philosophical, or are they based on observation? Are they persuasive to the common person?

• How does Ptolemy deal with competing hypotheses? Does he refute them in a logical way, by using reasoning and observations; or does he dismiss them out of hand?

• Why did Ptolemy’s work endure for so many centuries, considered as “The Greatest” contribution in the area of astronomy and cosmology? Were competing works available in this area, contradicting his conclusions? When and why did Ptolemy fall out of favor?