Sidereal OR Tropical Zodiac for Indian Astrology - PART 2

This is part 2 of sidereal-tropical zodiac debate which will focus on logical, scientific and historical aspect of it. The conclusive evidence from classical vedic and Indian astrology text has already been dealt in Part 1 here.

Part 1 of this article has settled and sealed the classical references aspect of this debate. As Indian astrology is entirely based on classical text which decisively talks about sidereal zodiac, Part 1 seals the deal for vedic astrologer or jyotishi.

Before I proceed, it's important to clarify a fundamental point. When we ask/debate "zodiac is tropical or sidereal" it may appear to novices that there are two different zodiacs. In reality, both these terms i.e. sidereal and tropical refer to the same ecliptical circle in the sky. There is only one zodiac. The difference lies in where is the starting point of the zodiac i.e. where do we count relative position of heavenly bodies from.

This part of debate has two aspects - history and astronomy/geodesy. Let's start with the historical aspect.

History of Sidereal and Tropical Zodiacs - seeds of controversy

I am not an expert in history but from a logical perspective I understand that there are two aspects about arguments based on history- factual evidence and theory. The credibility of evidence is one challenge. The other problem is with the theory. A theory is based only on available factual evidence which always runs the risk of being incomplete or incredible. There are also theories that are based on absence of any evidence of contradictory theory. Historical debate is also full of conjectures which could be anywhere from reasonable to ridiculous.

Indian astrology (Jyotish) is supposed to be very ancient but the limitation of history is within available records. The history of ancient sages in India far predates the recorded history. Indian astrology is an extension of the larger Vedic ecosystem which is too old to be captured in historical records.

I will try my best to use only credible evidence and debate with logical and reasonable conclusions.

From the available historical evidence, it is widely understood that zodiacal signs originated in Babylon and they followed sidereal way of reckoning signs. Spica or chitra nakshatra was the fixed point of reference in hypsomatic (Babylonian) zodiac as the opposite of 0 degrees Aries (more precisely few minutes of space ahead around 29 Virgo). In order to avoid being redundant and repetitive, I would summarize this point as - there is no historical evidence in public domain to show that zodiacal signs originated before Babylon and the original zodiacal signs were reckoned from stars and not equinox/solstice.

Most Indians might not agree with the first part of that sentence but then the hands of Indian siderealists are firmly tied at the back in historical debate because Indian knowledge is too ancient for this records driven baby history. Indians have always used sidereal and I have proven it in Part 1 already. So, the ancient zodiac is sidereal whether Babylonian or Indian, whichever you prefer to call as oldest.

Babylonian astronomy

Image courtesy : Project CSG

It's appropriate to point out that Babylonian astrology mentions about vernal point but nowhere in their text did they mention Aries begins at vernal point. According to Neugebauer who wrote about Babyonian astronomy, "Longitudes were not counted from the vernal point but from the sidereally fixed end points of the zodiacal signs" in History of Ancient Mathematical Astronomy (Page 594). The Greeks got too excited at the mention of vernal points and signs thinking they were fixed and created a new tropical zodiac out of it.

Francesca Rochberg in her book Babylonian horoscopes writes in page 45 under topic Planetary position in the ecliptic how the planets near Sun were reckoned from stars, not signs. The planets were reckoned from Sun but Sun himself was reckoned from? She writes the position of planets in the horoscopes which were conjunct Sun or "invisible" at the time of birth were expressed not in terms of degrees in sign but relative to star.

There was also a concept of "secret houses" (page 47) which were reckoned from stars. Sidereal system also uses the equinoctial point and adjusts the variation due to retro precession of equinox to correctly reckon from the star. The ancient guiding principle behind locating planetary positions is essentially sidereal - calculate the relative positions of planets from Sun (and equinox) then check/verify/adjust with fixed stars. The differences are found only in the manner the checking, verification or adjustment from star was done in different civilizations and times.

Those who are interested in details, the above conclusion (that earliest zodiacs were sidereal) is established by research done by Joseph Epping and Strassmaier in On Deciphering the Chaldean Astronomical Table (1881), The Recovery of Babylonian Astronomy, Astronomy out of Babylon (1894) and others like Kugler in Babylonian Lunar Reckoning in 1900 and J Schaumberger in Starlore and Starwork in Babel. Later researchers have only confirmed that ancients used sidereal zodiac irrespective of the purpose ie divinity, astronomy or astrology. (Courtesy Ken Bowser)

So what changed in history to shift from sidereal to tropical?

A brief about the birth of Hellenistic zodiac will give us a good answer. There was a Greek historian named Callisthenes who was nephew of famous Aristotle. Callisthenes accompanied Alexander as official historian in his military campaign towards the East. At the fall of Babylon in 331 BC, Callisthenes under guidance from his philosopher uncle Aristotle sent a considerable collection of Babylonian astronomical text/tablets to Greece. These tables and tablets were attributed to great Babylonian astronomer Naburimanni (Naburiannu). These text put the vernal-points at different places either Aries 8 degree, 10 or 15 degrees. (Courtesy: Cyril Fagan)

The Greeks who at that point had absolutely no idea that vernal points were moving retro, announced that vernal point was Aries 8 degree (another version adopted 10 degree). This was the birth of tropical zodiac in Hellenistic astrology. After Alexander's death, Romans too adopted this tropical zodiac. An ignorant mistake was about to become a colossal blunder in next few centuries.

The most important point to note here is that all this happened much before Hipparchus, who is credited to have discovered that equinox was moving. Hipparchus lived from 190 BC to 120 BC. That proves the ORIGINAL TROPICAL ZODIAC was devised under the ignorance of the fact that equinoctial point moves. The Greeks adopted it because they believed it was fixed. That is the irony of this debate. Also, the equinoctial point was not 0 degree Aries when tropical was invented (as detailed above).

Another surviving proof of the above historical fact can be seen in the collection of 180 Greek horoscopes in the book named Greek Horoscopes by Otto Neugebauer and H.B. Van Hoesen. This book has a collection of 180 Greek horoscopes from the post Hipparchus and mostly post Ptolemy era. Pliny the Elder, a Roman military general and author in 2nd century CE, wrote that "all these seasons commence at 8 degree of the signs (the winter solstice at 8 degree Capricorn)" in Natural History Bk XVIII, Chapter 59 Hohn Classical Library Vol 4, page 78). That's another proof of the fact tropical zodiac didn't tie Aries 0 degree to vernal points.

Tropical zodiac was devised in 331 BC but it was two centuries later when Hipparchus in 139 BC fixed 0 degree Aries at equinox. It however took another two and a half centuries longer when Ptolemy in 140 CE enforced Aries 0 degree at equinox in his treatise Almagest. An interesting fact - as late as 5th century CE horoscopes by Palchus placed equinox at Aries 3 degree (Greek horoscopes). The funniest part is - NOT one of those 180 Greek horoscopes use Aries 0 degree at equinox/solstice. This is pure historic evidence.

To summarize the history of tropical zodiac :

  • It was devised in 331 BC after fall of Babylon at the hands of Greeks and Babylonian astronomical text were taken to Greece.
  • Greeks assumed the equinox to be fixed when they adopted tropical zodiac after fall of Babylon.
  • The original tropical zodiac did NOT count 0 degree Aries at equinoctial point.
  • It took 500 years from 331 BC to 140 CE when Cladius Ptolemy standardized and changed tropical zodiac to fix 0 degree Aries at equinox.
  • Even after Ptolemy "enforced" 0 degree Aries tropical system, it didn't find any takers until many centuries (as established from Greek horoscopes).
  • Tropical zodiac since it's conception in 331 BC failed to become popular in 800 years.

So what could be the reason for rejection by astro community of the modern 0 degree Aries tropical? Was it that they were not logically convinced or was it not working out in practice? We can speculate on the reason but the fact remains equinox at Aries 0 degree was categorically rejected for many centuries as established (above).

What popularized fixing the equinox at 0 degree Aries as used today?

As already established, modern tropical zodiac was summarily rejected by astro community when Greek and later Roman empires were at their peak.

If one follows post Roman European history in the context of astronomy/astrology, there is hardly anything that explains the popularity of modern tropical zodiac better than dark age of Europe when independent thinking, scientific temperament, experiments and debates specifically of the nature as understanding our universe, planets and extra terrestrial entities is concerned were strictly forbidden and considered evil. Not only was there fear but also systematic deprivation of resources and environment to acquire scientific knowledge. That was precisely the time when the equinoctial gap between times was getting wider at the rate of 1 degree in 71 years (approx) but none in the Europe noticed or questioned the reason behind it.

Another possible reason could be the fact despite Almagest being written by Ptolemy in 2nd century CE, it was not translated to Latin until 12th century which means the majority of post Roman Europe didn't have the details of this zodiac but adopted it without having much of a chance to follow a more logical and scientific process to understand the merits of it. By that time, the factor of tradition had kicked in and a radical change in zodiac was too much to ask for then.

Astronomical and scientific aspect of the debate

The terrain of Astronomy and scientific facts is where modern tropical zodiac slips badly particularly in the face of post dark age revolutionary discoveries. The problem with the whole tropical argument is that back in the times, equinox/solstice were mostly used as a great computational tool before latitude/longitudes came to be used. It's a great tool to understand the annual and monthly spatial relationship between the Sun-Moon-Earth system instead of locating all planets in sky in reference to a point.

Copernicus crater

Image courtesy :

Here are simple facts. Hipparchus and Ptolemy, the originators of modern tropical zodiac believed in the primitive geocentric solar system ie. Earth at the centre and all planets (including Sun) revolving around earth. The Greeks of those days were highly confused about the relative motion of heavenly bodies. They didn't know if it was the earth or Sun that moved.

Earlier Greeks due to this specific ignorance assumed the equinoctial point was fixed. Hipparchus most probably knew about precession of equinox i.e. retrograde movement of equinoctial point but he in all probability didn't know what caused it. He and later Ptolemy assumed stars to be moving away from the equinox rather than the other way around which was again a major blunder due to ignorance.

The geocentric view of solar system made the equinox sacrosanct for Greeks because it's drawn using earth's equator. They projected the equinoctial point further in the space to impose the signs reckoned from earth's equator on other planets. The geocentric view which means no rotation, revolution or precession of earth was the root idea of forcing earth's equator on all planets. The logic is not tradition here but backward and ridiculous.

A star like Aldebaran (Rohini) in 5900 years sidereally moves only 10 minutes of space and a star like Antares (Jyeshtha) sidereally moves only 0.1 minute. So fixed stars are actually fixed in sidereal scheme of things. In tropical system however, all these stars move 83 degree in 5900 years from the equinox. That means even in thousands of years in sidereal scheme of things, we are pretty much looking at the same sky that the ancients in Babylon, Egypt and India looked at and located the position of planets.

Now which zodiac is stable, scientific and authentic? I think the answer is too obvious now.

Whenever I think of this sidereal-tropical debate, the first thing that amazes me is - why aren't tropicalist even for once thinking, "this tropical zodiac which is built around earth's equator was sermonised by the astronomers who thought :

  1. Earth is fixed, not rotating, not revolving.
  2. Sun was revolving around earth.
  3. Earth was the centre of solar system"

When Copernicus in 16th century CE proved that solar system was heliocentric ie Sun was at the centre and it was earth that rotated and revolved around Sun, the tropical zodiac should immediately have been given a dignified farewell because those who sermonized it, thought exactly the opposite of solar system. What Copernicus discovered, Kepler re-emphasized it with Sun as one of the focii of ecliptic of earth's orbit.

No wonder that Western astrology which was religiously using Ptolemy's tropical zodiac at that time fell out of favour among the masses and universities threw astrology out as people could smell dark age ignorance in it's astronomical logic and rest doubted it's practical application because of this geocentric folly of astronomical proportions. In contrast, Astrology never fell out of favour among the masses in India despite last 800 years of hostile and even barbaric rulers.

One logical question that should come to our minds is - we know that the Sun's apparent ecliptic and earth's equatorial plane do intersect due to earth's vertical tilt. So shouldn't that count for something in sidereal scheme of things? How can this scientific phenomenon be completely ignored by siderealists?

Very good question as sidereal system survives on logic and science. When Sun rises, vedic day starts which is called tithi (day of the month) in Indian astrology. This Sun rise defines the tithi, hora, ghatika, pal, vipal etc which are units of time in Indian astrology. Jyotish i.e. Indian astrology measures time from Sun rise. So the Sun and Moon dance relative to earth's equator is very much used in Indian astrology but it's scope is rightly limited to earth only.

A vedic day or tithi captures the angular distance between Sun and Moon with respect to earth. This is done to define the day and night cycle on earth, not Jupiter or Mars. So we are actually using the Sun's apparent movement in relation to earth's equator and that's what vedic time measurement is based upon as we are living on earth. But we do NOT use it to define the position of ALL PLANETS in space. The measurement of day and night cycle in Jupiter should be based on Jupiter's equator, not earth's. It's location in space shouldn't logically be measured using earth's equator. That is not the scope of earth's equator in sidereal scheme of things. This is appeal to science, logic and common sense instead of tradition. Tradition offcourse is good to have when we are on the right side of logic.


The conclusion can be drawn when we ask a simple logical question - why should we locate the space occupied by Mars or Jupiter in terms of spatial relationship between Sun and earth when we have a better and "fixed" reference point (fiducial) in stars who hardly move in thousands of years? The root of this tropical fallacy lies in 2000 years old geocentric view.

I think it's high time we realize that the elephant ghost of tropical child of the Dark age deserves a decent burial and needs to now rest in peace. There is more glory for the tropical zodiac in that instead of arguing for a Koranic idea of solar system in 21st century science driven heliocentric world.

The concluding Part 3 of the debate is my favourite as I am doing a comparative chart analysis for famous personalities like Hitler, Einstein, Tesla, etc. using the sidereal and tropical vedic charts. Proof of the pudding is in the eating.