What is a Parapegma?
A ‘parapegma’ is precursor to the modern day almanac. Originally it was a table that related star phases and corresponding weather predictions. Early versions were carved on stone, and had holes next to the descriptions, marking each day. The peg could be advanced each day, and on appropriate days the associated inscription would 'predict' certain astronomical and meteorological events.
The second century AD Alexandrian astronomer Claudius Ptolemy included a such a calendar in his work known as Phaseis—"phases of fixed stars and collection of weather-changes" the core of which is a parapegma, a list of dates of seasonally regular weather changes, first appearances and last appearances of stars or constellations at sunrise or sunset, and solar events such as solstices, all organized according to the solar year.
Ptolemy believed that the astronomical phenomena caused the changes in seasonal weather; his explanation of why there was not an exact correlation of these events was that the physical influences of other heavenly bodies also came into play. Hence for him, weather prediction was a special division of astrology.
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