With the modern emphasis on natal astrology, natural astrology is sometimes forgotten. This is the branch of astrology that is more concerned with nature than with humans. Its traditional subject matter has been tides, weather and climate, volcanic eruptions and earthquakes, animal behaviors, agriculture, and plagues. This article gives a brief overview of natural astrology beginning with Ptolemy.
The Harmonics  is probably earlier than the Tetrabiblos. Although Ptolemy is well known for his astronomy and astrology, he was also one of the ancient sources for theories of harmony.
The work studies this universal field of knowledge for which music and geometry are considered subsets. Much of the material in Harmonics is exclusively concerned with music, including setting up exact number ratios for the different modes.
The Harmonics Book III applies his previous exposition of intervals, scales, and ratios to ethics and psychology, and to astronomy and astrology. Unfortunately, some of Book III has been lost to us. In Chapter 9 of Book III, Ptolemy presents the astrological aspects and their ratios to one another. Curiously, in this presentation Ptolemy does not use degree numbers for the aspects. Instead, he considers the twelve zoidia as discrete units and the whole number relationships between them that yield moriai and epimoriai. This discussion might have fit better into the Tetrabiblos Book I, within his treatment of the qualities and relationships between whole zoidia.
It has been said that we each stand on the shoulders of those who have gone before us. I know this to be true in my own life, and I know from my studies at Kepler College that it is also true in the field of astrology. Over the twelve months, I have read a great deal about Ptolemy. And while I still don’t understand everything he said or did, I am amazed at what he and the ancients accomplished without modern technology. I am also amazed by the great scientific minds that continued to evolve the ancient science of astrology forward by not only building upon the previous generation’s foundation but also by expanding it.