Finally, we’ve arrived at the end of Book III where we’ve arrived at a well developed model of the solar motion. But before closing out, Ptolemy has one last chapter to discuss the inequality of the solar day. Ptolemy states the problem as follows:
the mean motions which we tabulate for each body are all arranged on the simple system of equal increments, as if all solar days were of equal length. However, it can be seen that this is not so.
What Ptolemy is really getting at here is that the term “day” is somewhat ambiguous. As such, the different ways by which we might measure a “day” are explored in this chapter. Continue reading “Almagest Book III: On the Inequality of Solar Days”