Horary astrology is a branch of western and Indian astrology that is used to answer a single specific question by casting an astrological chart for the moment that the question is asked.
The premise is that the chart cast for the moment of the question will contain some information about both the nature of the question as well as the outcome or answer.
Horary astrology is also known as interrogational astrology. In India it is known as prashna (or prasna), which means “question” in Sanskrit. In Arabic it is known as masa’il, which means “questions” or “interrogations”.
Interrogational astrology is technically the earlier and more accurate designation for this branch of astrology, although it has become more common to refer to it as horary astrology in English. “Horary” itself just means “of the hour”, and the English convention seems to have been introduced in the 17th century by astrologers who would refer to “horary astrology questions”, which means “hourly questions”. Eventually the phrase was shortened from “horary astrology questions” to simply “horary astrology”.
In practice, most horary astrologers cast the chart for the moment that they receive the question from the querent or questioner, which seems to imply that for some astrologers horary is about the exchange of a question between two parties, rather than just casting a chart for the birth of the question itself. However, whether or not astrologers can pose horary questions to themselves is sometimes a point of contention amongst practitioners.
Horary astrology is traditionally one of the four major branches of western astrology. Some have speculated that it was the latest branch to have been established, with some of the earliest complete texts on horary dating to the early Medieval period (5th through 8th centuries CE).