So far (see previous parts) I feel confident that about 2,000 years ago we mistakenly projected one zodiac system upon another. And logic has me fairly well convinced that the original system was tropical, and sidereal was the mistaken projection. The logic is that the qualities of the twelve divisions are all rationally derived from tropical phenomena, not sidereal phenomena. What I am really interested in now is what the historical authorities of astrology have to say about this. Do they describe the twelvefold zodiac as tropical or sidereal?
As I mentioned at the outset, my astrology background is Indian (or “Vedic” as they say). So I am mainly concerned with Indian historical authority.
Most historical textbooks on Indian Astrology are entirely concerned with how to interpret the planets, not how to calculate their locations. India traditionally divides astrology into three branches: calculators, interpreters, and omen readers. The experts in one branch are not experts in another, since each branch is so vast. Thus, I will focus my attention of historically authoritative books on Indian astrological calculation.
Sūrya Siddhānta & The Veda
The most authoritative Indian text on astrological / astronomical calculations is without a doubt the Sūrya Siddhānta, a title which declares the book to be “Perfect Conclusions of the Sun.” The 13th text says that the twelve signs of the zodiac are determined by the months of the year, distinct from sidereal, cival, and lunar clacluations given in the immediately previous words and verses. Thus Sūrya Siddhānta describes the twelvefold zodiac tropically.
The 27th text says that all calculations of planetary positions should be made in reference to the sidereal nakṣatra, not the twelvefold tropical zodiac. These positions are later converted to tropical coordinates. I will elaborate on that later, but first there is something quite fascinating in this 27th text.
It states that planets complete their journey through the stars when they come to the end of the constellation Revatī. Sidereal astrologers align the end of Revatī with the end of Pisces. Thus Sūrya Siddhanta says that the planets “begin” their movement at the beginning of the nakṣatra after Revatī: Aśviṇī, a constellation Siderealists say defines the beginning of Aries.
What is really exceedingly fascinating, though, is that the oldest existing Indian texts mentioning constellations extensively (The Yajur Veda (Black) and the Atharva Veda) list Kṛttikā as the starting point, not Aśviṇi! This all makes sense, too! Because due to the precession of the equinox, the start of the tropical zodiac – the vernal equinox – was in Kṛttikā (spaning sidereal Aries and Taurus) when those older Veda were written. And by the time the current version of Sūrya Siddhānta was penned, the precession had moved the equinox to Aśviṇī. So, what we are seeing is that Indian sages of old did consider the equinox to be the true start of the zodiac, and they update their statements regarding which is the “first” sidereal constellation (nakṣatra) depending on where the equinox has precessed to at the time of writing.
Sūrya Siddhānta itself tells us (in text 9) that it is periodically re-written and updated to keep in sync with various astronomical modulations, precessions, and irregularities. So it is quite loyal to accept that the astronomical texts of India are periodically updated through the centuries.
The difference between the older Vedas and the newer Sūrya Siddhānta regarding which sidereal nakṣatra is considered to align with the start of the zodiac shows that Indian sages accounted for the precession of equinoxes, and that they considered the equinox to be the true start of the zodiac and kept their writing on the cross-reference of tropical and sidereal points up to date.
The 28th text tells how to divide the zodiac circle into arc-measurements of seconds (vikalā), minutes (kalā), degrees (bhāga), and sign (rāśi). This confirms that the ancient Indian sages did not use actual constellations to measure the zodiac, but rather used mathematic divisions based on the 12:1 ratio of the Moon’s motion relative to the Sun.
Sūrya Sidhhānta then explicitly defines the 28 sidereal constellations: nakṣatra – lunar mansions which any novice of “Vedic astrology” must of course be familiar with. The book then defines the difference between sidereal and tropical locations: ayanāmśa – a term that literally means “distance to the equinox.” The modern technique is to calculate a tropical position and apply ayanāmśa to determine the sidereal equivalent. The Sūrya Siddhānta’s method is opposite. It first calculates planetary positions in reference to sidereal stars (nakṣatra) and then applies ayanāmśa to locate the equinox and the tropical position.
Why bother to locate the tropical position if the zodiac is supposed to be read from a sidereal perspective!? Indeed, Sūrya Siddhānta instructs us to convert sidereal calculations to tropical positions so that we can then figure out the ascendant.
If you know how modern Indian zodiac calculations (and I presume all modern sidereal astrology?) are done, you are now a bit shocked, because it is exactly backwards. Sūrya Siddhānta says to convert sidereal positions to tropical and then figure out the ascendant. Modern astrologers, however, figure out the tropical ascendant and planets first, and then convert them to sidereal positions. Sūrya Siddhānta, however, does not ratify this practice. The Siddhānta never instructs us to convert tropical positions to sidereal ones.
The Ascendant is Inherently Tropical
This brings up an interesting logical point. What is an ascendant? It is the location of the Earth’s eastern horizon. This has nothing to do with a star and everything to do with the Earth and the Sun’s relation to it (Sunrise). Therefore you can not calculate the ascendant without a tropical zodiac. It is literally impossible. That is why Siderealists must start with tropical calculations and convert them.
But isn’t that really excruciatingly intriguing: the ascendant is by nature tropical!? The ascendant is the very foundation of a natal horoscope. If that very foundation is intrinsically a purely tropical entity – what does that tell you about which zodiac should be used for natal astrology?
Returning to the authority of Sūrya Siddhānta I will conclude with a reiteration. The book instructs us to convert sidereal positions to tropical, not visa vera. Once everything is converted to tropical the ascendant can be determined and a horoscope cast. Thus it seems quite convincing that the Sūrya Siddhānta conceives of the twelvefold zodiac in a tropical manner. And although it is a book about calculations, not interpretations, it indirectly indicates that tropical coordinates are to be used for interpretations due to the fact that it never instructs us to convert anything from tropical to sidereal.
The Yajur Veda has an appendix called “Jyotish” (the namesake of astrology in India) – but this treatise does not touch at all upon natal astrology or planetary calculations. It concerns itself with correct calendars for religious and cultural events (a sub-branch of calculative astrology). This “Vedānga Jyotiṣa” does however describe that the twelvefold division of the Sun’s paths corresponds directly to the months and seasons determined by the equinoxes and solstices.
The Bhāgavata is extremely revered and famous, primarily for its poetic beauty, philosophical completeness, and theological harmony. It is thought of as the full expansion of the Gāyatrī Mantra, a commentary on the philosophical conclusions of Vedānta Sūtra, and the final Pūraṇa representing the full maturity of Indian thought. Right in the middle of the Bhāgavatam, in the 5th division, there is an elaborate astronomical description of the universe.
5.21.2-6 reveal that the Bhāgavatam considers the twelvefold zodiac to be a tropical entity, not a sidereal one: “Outer space is measured by relation of heaven and earth,” it says. “The Sun is the king of all the planets, in the center of everything, keeping everything together. It moves to the north, crosses the equator, and moves to the south. When it goes north of the equator days get longer. When it crosses the equator days and nights are equal. When it goes south of the equator days become shorter. On this basis the Sun moves through the twelve divisions called Capricorn and so forth.”
Here it is clearly declared that the equinoxes and solstices are the basis for the twelvefold zodiac divisions such as Capricorn and all the rest. In other words the Bhāgavatam declares the zodiac to be tropical. It makes this explicit: “The Sun is at Aries and Libra when the days and nights are equal. Passing through Taurus, etc. the days become longer and then decrease until again equal with the night. Passing through Scorpio, etc. the night becomes longer and then decrease to again become equal with the days.”
It cannot be denied that the Bhāgavatam considers the zodiac to be tropical.
Both by logical rational and reference to authority it is apparent that the correct twelvefold zodiac is tropical. There is another division of the zodiac which has 27 or 28 sidereal constellations (nakṣatra). It coexists with the twelvefold tropical zodiac, yet is independent from it due to precession of the equinox.
END OF PART IV.