Horoscopes of the Moon: Weather Prediction as Astrology in Ptolemy’s Tetrabiblos

Claire Hall

doi:10.1163/15733823-02630018

Abstract

Abstract Ptolemy’s Tetrabiblos is not usually considered as a meteorological text. I examine the sections of the Tetrabiblos that deal with weather prediction and argue that Ptolemy considers it part of astrology. I show that the way Ptolemy categorises weather prediction differs significantly from other Greco-Roman writers, including Cicero (On Divination) and Sextus Empiricus (Against the Astrologers). I argue for these conclusions: first, that Ptolemy considers weather prediction to be part of astrology – i.e., a scientific practice which includes giving an account of the causes of phenomena with reference to the stars; to give such an account for the weather requires a practitioner to go beyond the observation and cataloguing of weather signs. Secondly, I argue that understanding weather prediction as astrology means that the distinction between horoscopic and general astrology is more fluid than is sometimes thought. Finally, I will show that Ptolemy’s views on weather prediction provide a case study for his view of astral causation.

Highlights

Ptolemy wrote about weather in several places in his work
I examine the sections of the Tetrabiblos that deal with weather prediction and argue that Ptolemy considers it part of astrology
I argue for these conclusions: first, that Ptolemy considers weather prediction to be part of astrology – i.e., a scientific practice which includes giving an account of the causes of phenomena with reference to the stars; to give such an account for the weather requires a practitioner to go beyond the observation and cataloguing of weather signs

Summary

Introduction

Ptolemy wrote about weather in several places in his work. His Phases, an almanac of weather signs for each day of each month, reads quite differently from his more widely read theoretical works like the Almagest or the Tetrabiblos. He suggests, one should think about other causes which could be at play in weather conditions, including planetary transits, the dates of the new and full moon, and the nature and qualities of the planets’ configurations at the time.[5] If the main body of the Phases offers only a conventional parapegma-style catalogue of weather signs, what does Ptolemy mean by saying that we should take into consideration the moon, the sun, the effects of the planets and their aspects? I argue that Ptolemy uses the weather as a clear example of astral causation – both directly (the stars cause weather conditions) and indirectly (the stars cause regional weather which has an effect on human characteristics)

Defining Weather

Weather as Astrology in the Tetrabiblos

Weather and Astral Causation

Conclusion