I am familiar with both zodiacs myself and use the tropical zodiac for matters relating to our solar system, but also am aware where the various objects beyond our solar system are located, which is a form of sidereal astrology I suppose. However, I do not use sidereal ayanamsas, although I have investigated many of them.
My interest here is to point out that one ancient Sanskrit text and the primary text associated with astrology in the Buddhist tradition, the “Kalacakra Tantra” (Wheel of Time Technology), and the commentary “The Stainless Light” from the Vimalaprabha, make it clear that at least in that system, it is the tropical zodiac and not any of the sidereal zodiacs that is indicated and was used.
Those of you who really care about this issue will no-doubt enjoy this book by the distinguished scholar Edward Henning.
Kalachakra and the Tibetan Calendar by Edward Henning
Edward Henning is a mathematician, physicist, linguist, and Buddhist scholar, fluent in Tibetan and other languages.
This 408 page book is published by the “Treasury of Buddhist Science” series, from the American Institute of Buddhist Studies at Columbia University in New York, and with an introduction by the distinguished Buddhist scholar Robert A. F. Thurman. Henning’s book is available on Amazon.com in hardback.
I have been in correspondence with Henning for some years, and he was kind enough to do some translation from Tibetan to English for my book “Tibetan Earth Lords: Tibetan Astrology and Geomancy,” which is also available on Amazon.com.
Here is a quote from Henning’s book, but again, to understand the whole background of this topic, reading the book is indispensible.
“Looking at the description of the calculations for the calendar in the Kàlacakra Tantra commentary, the Vimalaprabhà, translated in chapter five, it strikes me that the Kàlacakra system expresses a reforming spirit, criticizing the loss of accuracy in general Indian systems and encouraging the proper use of a tropical zodiac based upon the observation of solstices.
“It is certainly true that around the sixth and seventh centuries C.E. Indian astronomers paid little - perhaps too little - attention to the effects of precession. In his translation of the Sårya Siddhànta (Sårya, p. 117), Burgess writes that "the earliest Hindu astronomers were ignorant of, or ignored, the periodical motion of the equinoxes". He also considers the possibility that the Hindu adoption of the sidereal system was the result of "a failure to recognize the fact that the equinox was variable."
“He goes on to describe how difficult it would have been for them to fit corrections for precession into their theories and calculations once they had finally realized the important effect it was having. This is a cogent point, and the Vimalaprabhà criticizes the Indian heterodox astronomers for creating complex systems that they eventually themselves failed to understand, and that subsequently became inaccurate with the passage of time.
“These views expressed by Burgess are very similar to my interpretation of the Kàlacakra criticism of Hindu astronomers - that they had drifted by neglect into using a sidereal zodiac. It is this error that the Kàlacakra authors want to see corrected in a reform of the calendar. A Kàlacakra point of view would accept the basic structure of the Indian calendar and its symbolism, but adjust it to the tropical zodiac. Not by some tortuous manipulation of theories and complex calculations as in the Hindu siddhàntas, but by the simple application of observation.
“In the Vimalaprabhà this could hardly be expressed more clearly, and the order in which these topics are presented in both the Kàlacakra Tantra and it's commentary make sense when viewed in this way.
“To recap, at the very beginning of the section describing the calculations the Vimalaprabhà explains that there are inaccuracies in the calculation systems in use at that time in India - it calls them corrupt - and explains that this is due to an inaccurate knowledge of the solar longitude.
“It then explains that this inaccuracy comes from not using the shadow determination of the solstice to correct the solar longitude, and that if as a result the solar longitude is wrong, then all the planetary positions will also be wrong. It then states that if the positions of the Sun and the planets are wrong, then any astrology performed using these positions will be meaningless.”
Those of you interested in this very controversial topic will want to read Henning’s book and form your own opinion based on his research and elucidation.
My point here is that we should be open to new ideas, or in this case old ideas that have been there all along.