Aristotle's Explanation of the Halo

In Meteorology book III, Aristotle offers an explanation of why the halos that occasionally appear around the sun and moon are perfectly circular. His explanation is remarkable in that it involves what is probably the oldest surviving lettered geometrical diagram. Modern commentators have criticized the explanation itself as being empty or circular (in the wrong way). In this talk I will try to show that is a misunderstanding, and that the explanation shows an interesting quantitative side of Aristotle's scientific method that is often ignored or denied to exist. Further, the explanation is clearly superior to all other explanations of the same phenomenon offered by his predecessors, and has had a direct influence on all successive explanations of the halo, including those found in modern textbooks of atmospheric optics.