A tropical zodiac or the tropical zodiac?
Ancient and even medieval astrologers didn’t always understand precession, and therefore often tried to relate the zodiacal signs both to the constellations and to the seasons. (Some believed in trepidation, a back-and-forth motion of no more than 8° either way.) As a result, some modern astrologers have tried to fudge the issue by claiming that the ancient authors cannot properly be called siderealists: if they conceived of their zodiac as being constant relative to the seasons, the argument goes, it was a tropical zodiac.
There is a grain of truth in this, and the difference between the two models is certainly starker today than it was in Ptolemy’s time. But the fudging lies in conflating two meanings of the word ‘tropical’. If an ancient author believed the zodiac to be constant relative both to the stars and to the seasons, then in that sense it would have been conceived of as both tropical and sidereal at the same time. The real question, however, is the starting point. Were the ancient authors using the tropical zodiac, that is, the default zodiac of contemporary western astrology that equates 0° Aries with the equinox? The answer is that they were not. For example, Vettius Valens, a contemporary of Ptolemy’s, states near the beginning of his work: ‘From its first degree to the equinox, [Aries] is stormy, full of hail, windy, destructive […] This sign has 19 bright stars.’
A ‘tropical zodiac’ that does not begin with the equinox immediately loses its two main selling points: the pleasing symmetry of the rising times of the zodiacal signs and the unambiguous definition of 0° Aries. Sidereal astrologers differ slightly on the exact fiducial star, or on the exact current offset of 0° Aries from the equinox (often known by the Sanskrit term ayanāṃśa). To be sure, this is a minor annoyance, similar to but smaller than the discrepancies between different systems of house division. But while the standard tropical zodiac may be more convenient in this respect, convenience and astrological usefulness are not the same. We don’t want to be like Mulla Nasruddin in the well-known Sufi story, looking for his lost key under the street light because his house, where he had lost it, was too dark!
The astrological consultation work offered on this website is all done from a sidereal perspective. To take the Primary Directions Diploma Course, however, you do not have to be a siderealist: the core technique of directions is zodiac-independent, and students are free to work in the zodiac of their choice.