I recently read a research study on another forum comparing the SZ with the TZ and the SZ came up on top. The researcher mentioned that the ayanamsa used was Fagan/Bradley. One of the other forum members asked why Fagan/Bradley was used? In other words, why did you use that sidereal zodiac (not included but implied: when there are so many other sidereal zodiacs out there) ?
The truth is that there are many sidereal zodiacs out there, just how many it’s impossible to tell but the popular Swiss Ephemeris astrology library used by many software developers provides 21 ayanamsas in their package. That is, 21 sidereal zodiacs! There are others not included and new ones are showing up all the time.
It would be nice if it could be decided once and for all which one (if any) is correct but how can that be done? So far, the astrologer uses their ayanamsa of choice because “it works”! Truth to tell, any ayanamsa “will work” a good percentage of the time on a chart-by-chart basis. Also, it “works” because it’s the only one used, having been adopted from the guru, teacher or system from which it was learned. So, how can you realistically test x numbers of sidereal zodiacs?
Obviously, testing each ayanamsa on a particular chart won’t lead to convincing results. What is needed is a study designed to test multiple ayanamsas against large data sets to see if any stand out significantly. As yet, not much has been done in this area.
A search of the literature turns up only three attempts to find the “right” ayanamsa:
1. The research of Cyril Fagan and Donald Bradley which rectified the Lahiri ayanamsa by studying thousands of events with solar and lunar ingresses. The result was the Fagan/Bradley ayanamsa used by the majority of western sidereal astrologers. However, the details in the form of a formal study were never published so the results can’t be replicated.
2. “The Sun in the Lunar Mansions”, Overbeck, 1980 : A statistical study of the solar positions of 2,492 Clergy in 3 different zodiacs and 4 lunar mansion schemes. This was a replication of a previous study and compared Lahiri, Fagan/Bradley and tropical zodiacs.
3. “Ayanamsa Statistical Study”, Overbeck, 2008: A statistical study testing 25 Ayanamsas applied to the moon in the lunar mansions or nakshatras, against 12 large data sets of timed births from the Gauquelin archives.
The last was specifically designed to test the Swiss Ephemeris ayanamsa set plus a couple of others. It was not meant to be definitive but rather it was hoped it might encourage others to work in this area. Both of the two studies above can be found on the Article page at: http://home.valornet.com/overbeck/Articles.html
It is sidereal astrology’s main embarrassment that it has no agreed upon starting point. Until this is resolved the question will always be: “Which sidereal zodiac are you using?”. A question never asked of a tropical astrologer.