I'll reply to your post in conversation mode. I think it will be easier to follow that way.
[Michael:] Let me see if I understand you correctly:...Many Vedic astrologers have chosen to use the sidereal chart even though they were aware that the early Sanskrit texts clearly point out that the tropical is what they used – way back then.
[Therese:] No, that isn't the way it is. Jyotish astrologers aren't aware that some principles of India's astrology are transplanted from the west. They'll probably never believe, for example, that the concepts of cardinal, fixed and mutable signs are straight out of Ptolemy and are directly related to the change of seasons. (I have an article on this on my web site.) http://users.snowcrest.net/sunrise/LostZodiac.htm
(The Lost Zodiac, Part 5)
Jyotish astrologers also follow the zodiac that has been used in India for centuries. Just like in the west where astrologers haven't been aware that the earliest western astrologers used a sidereal zodiac. It hasn't occurred to either group of astrologers (east or west) that there's another zodiac out there that might be worth investigating.
(It's true that in recent times a few astrologers in India are looking at the tropical zodiac, but this isn't traditional. Similarly in the west some tropical astrologers are looking at the sidereal due to the work of Jyotish groups.) This is all new and exciting, isn't it?! We're having a tropical- sidereal dialog which was unheard of a few short years ago.
[Michael:] As an astrologer, I well know that we test out the techniques we use on our own charts, those of our family, friends, and any other charts that we key on. In that regard, it is very personal. At the same time, we often ask other astrologers to give us reasons beyond a simple "it works best for me."
[Therese:] Yes, that's the way it is exactly! With astrological computer databases we've finally reached the time where we can do some mathematical testing of zodiacs.
[Michael:]In the case of the sidereal vs. tropical discussion, this has been going on around me for most of my astrological life. I had the temerity to invite a number of siderealists to come and live at our center (Heart Center), often for years at a time. We had Sanskrit scholars, Hare Krishna scholars, Swamis, and even a western siderealist – none other than Gary Duncan.
In general, my experience in this environment of siderealists was that they were passionate and even quite aggressive about their belief in the sidereal system.
[Therese:] Yes!! No one could get alone with western siderealists, who based their sidereal conviction on solar and lunar return charts and planet angularity. After my ten years as a tropical astrologer, I joined that group for a short time, then changed to India's astrology. (Which I don't call "Vedic" because horoscopic astrology didn't exist in Vedic times. Robert Hand and others agree that the term "Vedic" isn't really correct for India's astrology, but it's a lost cause because "Vedic" became the official western term when the ACVA was formed. India never used the term "Vedic" for its astrology before the California conferences in the early 90s where "Vedic" was coined. I was there. I saw it happen. I was a founding member of the ACVA but dropped out because of what I perceived as a rigidity that I wasn't comfortable with. It's like the "fix" was already in.)
[Michael:] Not one of them ever pointed out to me that the roots of Vedic astrology were in the tropical zodiac or that at some point in history practitioners decided to go sidereal, based on their personal use and research.
[Therese:] That isn't quite correct. Astrologers were using the sidereal zodiac in Ptolemy's time. His concepts were adopted by astronomers, and made their way into the literature, but astrologers themselves continued with a sidereal zodiac. As a matter of fact, it was a western astrologer who discovered the early use of the sidereal zodiac--Nick Kellerstrom.
There was no sure way of knowing this early history until the recent translations by the three Roberts (Schmidt, Hand, Zoller) in the 90s. We also have the academic scholars: Pingree, Neugebaurer, Rochberg, etc. There's no doubt that early western horoscopic planetary placements are sidereal. (I have some of those horoscopes on my web site.)
The main point is that when all the Hellenistic texts were written, India eagerly adopted those texts. At that time there was no tropical-sidereal controversy. Astrologers didn't know what zodiac they were using. They simply continued with the zodiac inherited from Mesopotamia (whch was star based.) Zero Aries tended to move around, and several different sidereal zodaics were used, but they weren't tied to the equinoxes and solstices. There was no astrological tropical zodiac before Ptolemy. The solstices and equinoxes were astronomical, but not astrological. These two are confused in Jyotish literature, but quite clear in the ancient Hellenistic translations.
[Michael:] I am not sure what we can even expect from this discussion, except that the uninitiated folks like me probably need to know that behind current Vedic sidereal ayanamsas stand the tropical positions, historically speaking.
[Therese:] The discussion is valuable in that we're seeing the different sides of a knotty problem. We're not anywhere near a resolution, but as astrologers we can continue with the challenge. It will keep our minds young! As moderns we can continue to test the zodiacs in various ways and (I suppose) continue to argue for a correct zodiac.
The difference between Ernst and myself is that (if I'm reading him correctly) Ernst has faith in the antiquity and truth of India's texts. Because I've studied the western Hellenistic translations and compared them to Indian texts, I've observed that India's texts are a grand collection of eastern and western ideas including much material from Ptolemy--who invented the concept of an astrological tropical zodiac. Because of my education I've been trained in scientific thinking, so I had to be as objective as possible. As I said, I had to give up my faith based belief in the superiority of India's texts.
I'd say that I've been a scholar (specializing in astrology) for most of my .life, and Ernst has been an astrologer with a deep reverence for what he sees as Indian wisdom. This is the old science/faith dichotomy that has probably been around since human beings have peopled the earth. But we're fortunate that today with the internet we can openly discuss and test astrological principles. It's an exciting time to be alive.