The Sidereal vs. Tropical Debate

By Vaughn Paul Manley, M.A.
Copyright 2010. All Rights Reserved.

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It’s important to clearly understand the difference between the two zodiacs, the Vedic or sidereal, and the Western or tropical, and their respective places in the world of astrology. Without this understanding it’s easy to think that one system is superior or inferior to the other and disregard their relative value.

So why two zodiacs anyway? Isn’t one enough? After all, one sky seems to have worked out quite well - thank you very much. God made no mistakes there! One zodiac belt, about 18 degrees wide, with the 12 zodiac signs ranging from Aries to Pisces rising in the eastern horizon - no problems there. It’s just astronomical fact. The stars shine equally on everyone, whether they’re standing in New Delhi or downtown L.A., so why one “sidereal” zodiac popular in the East and one “tropical” zodiac popular in the West?

First of all both zodiacs are exactly the same in the sense that there are 12 zodiac signs progressing from Aries to Pisces. The elements – fire, earth, air, water; qualities – cardinal, fixed and mutable and general characteristics associated with each sign are basically the same in both systems. Up until the last century or so, before the discoveries of Uranus, Neptune, Pluto and Chiron, the classical rulerships of the signs were used in both systems.

The classical sign rulerships are as follows: Mars rules Aries and Scorpio, Venus rules Taurus and Libra, Mercury rules Gemini and Virgo, the Moon rules Cancer, the Sun rules Leo, Jupiter rules Sagittarius and Pisces, and Saturn rules Capricorn and Aquarius.

The difference between the two zodiacs, therefore, is not so much the content of the zodiac but in the calculation of the starting point of the 1st degree of Aries.

In Western or tropical astrology the calculation of the Sun passing through the 1st degree of Aries is marked by the Spring equinox or March 21st. By extension, if you take out your Western ephemeris you’ll note that the beginning of each season is lined up with the Sun passing into each of the cardinal signs in the zodiac – Aries, Cancer, Libra, and Capricorn. The tropical zodiac, therefore, is a symbolic system based on the Sun/Earth relationship and is oriented to the seasons.



In Vedic or sidereal astrology the calculation of the Sun passing through the 1st degree of Aries is marked by the Sun passing through the actual observable fixed stars making up the constellation Aries and has nothing to do with the seasons. “Sider” means “star” and therefore sidereal astrology is based on the actual astronomical positions of the planets against the backdrop of the fixed star constellations. The sidereal zodiac is not symbolic but is oriented to an observable phenomenon. A sidereal ephemeris will correspond to the positions of the planets as recognized by modern astronomy.

David Frawley writes in his book, The Astrology of the Seers, that “The sidereal zodiac is probably the original zodiac historically, as it is the observable zodiac. The tropical, which is an abstract zodiac, must have been derived from it, as all abstractions are usually based on underlying observable things.”

An astonishing thing to contemplate is that the ancient Vedic rishis were aware of the fact that the earth changes its tilt or “wobbles” on its axis. Many centuries before the Europeans were debating over whether the earth was flat, the Vedic rishis were figuring out exactly what effect the Earth’s wobble would have on the calculations of their ephemeris’s!

Without the aid of telescopes or modern technology they calculated that the orientation of the equinoxes to the fixed stars precedes or moves backwards through the zodiac at a rate of about 50.3 seconds per year, or about 1 degree every 72 years. That they were actually able to calculate this gives us a clue as to how advanced the ancient Vedic civilization was in terms of mathematical and astronomical knowledge.

This phenomenon is known as the Precession of the Equinox. In other words, where the Sun actually is at the time of the Spring equinox moves backward through the zodiac. Vedic or sidereal astrology calculated the the Sun at 6 degrees 03 minutes of Pisces at the Spring equinox in 2003. Therefore, the current mathematical difference between the two systems is about 24 degrees. However, you will often hear it said that you need to subtract 23 degrees from the planetary degrees in your Western chart to arrive at your Vedic chart. This is because most people interested in Vedic astrology were born closer to 1950. On January 1st 1950 the difference was 23 degrees 09 minutes.

This mathematical difference between the sidereal and the tropical zodiacs is called the “ayanamsha” in Sanskrit. Ayana means "precession" and amsha means "part" or "portion." The term refers to the number degrees difference between the Spring Equinox and the 1st degree of Aries.

However, to further complicate matters there are several commonly used ayanamshas that vary by nearly 2 degrees from one another. Of these, the most widely used ayanamsha by Vedic astrologers worldwide is the Lahiri ayanamsha, also called the the Chitrapaksha ayanamsha. This was developed by N.C. Lahiri, the former head of Astro-Research Bureau of Calcutta. In 1954 the Lahiri ayanamsha was given the stamp of approval by the government of India.

Historically, it’s generally agreed, that the two zodiacs were in alignment with one another about the year 285 A.D. with both sidereal and tropical ephemeris’ listing the passage of the Sun into Aries at the Spring equinox. What happened next? What went wrong?

I don’t know that anything went “wrong.” Obviously, our civilization was meant to have both zodiacs. Both systems, after all, are looking at the same phenomenon of the planets moving through the sky, but from different vantage points. The question is what sign constellation do you assign to the planets? Western astrologers prefer to line up the planets in the zodiac according to the seasons, whereas Vedic astrologers prefer to orient them to the fixed stars.

Interestingly, due to the precession of the equinox, the Sun will be at the 1st degree of Libra at the spring equinox in about 11,200 years! Mark you calendars! Then we’ll really have a lot of explaining to do with regards to the two systems because they’ll be exactly opposite one another!! The ayanamsha will be 180 degrees 0 minutes!! I’d say it’d be worth it to incarnate at that time just to join in the debate!

Let’s face it - we’re basically creatures of habit. We tend to feel comfortable with what we’re used to and resist change. It’s hard to be clear and objective when we feel threatened in any way and it’s easy to dismiss a seemingly opposing viewpoint to save having to expand out of our comfort zones.

I think God gets a lot of mileage out of people debating and facing their emotional reactions that surface in the process. Take, for instance, how debating is an integral practice in the training of Tibetan Buddhist monks in the qualities of understanding and compassion. Eventually their resistances are broken down and they’re able to contain a broader, more all encompassing viewpoint.

The debate between the two zodiacs is, of course, centered around one main question, “how can both systems be right?” How can I be both an Aries in the Western system and a Pisces in the Vedic system?

It could be argued, first of all, that it’s rather simplistic to identify yourself by only one particular sign like we tend to do in the West. This is more of a recent cultural phenomenon due to the popularization of horoscope columns. In the more distant past, Western astrology was oriented more to the ascendant than the Sun if it had to be limited to one sign. Vedic astrology today favors the emphasis of the ascendant and the Moon over the Sun as well.

This makes sense because the ascendant is the starting point of the horoscope and the quickest moving indication in the chart so is could be considered more personally associated with your identity or “you.” In practice, the ascendant or 1st house relates more to one’s self, identity and personality traits than any other house.

However, if you asked someone in India “what’s your sign?” they would likely assume you mean their Moon sign, since Vedic astrology is a Moon-based system and it’s primary predictive systems are based on the Moon.

The obvious reason why emphasizing one sign is limited is that there are so many potential configurations from which to interpret the same descriptive traits. For instance, your Sun may move from Aries to Pisces in your Vedic chart, but you also may still have three planets in Aries, or Mars in Aries. You certainly would tend to see strong Aries traits in the Vedic chart even though the Sun is not involved.

In fact, in my experience that’s always been the case when I look at both the Vedic and Western charts of a particular person. They’ve never contradicted one another when the chart as a whole is considered.

Some people say that your Western chart is more “earthy” and represents your personality and your Vedic chart is more “spiritual” and represents your soul. This makes some sense due to the relative vantage points in terms of distance. In other words, the stars are further away than our Sun, which is the closest star.

On the other hand, this seems to imply that your Western chart is more grounded in practical matters on Earth, and your Vedic chart is more spiritual and ethereal. Whereas, the opposite could be argued to be the case because your Vedic chart is related to the actual observable fixed stars and your Western chart is symbolic. This is why some argue that your Vedic chart can be so accurate for prediction with actual events on Earth and your Western chart is better for describing the psychological effects the actual events may have on your psyche.

I think that what’s important is the realization that the zodiac represents an archetypal evolutionary pattern beginning with Aries and ending in Pisces. As an illustration, the pattern of 12 signs can be visually likened to a clock. Whether you rotate the base to get your sidereal Vedic chart or the tropical Western the clock still works at least symbolically if not literally because it’s based on a true fundamental pattern.

This is why I think Western astrology makes sense even though it uses a symbolic zodiac. Our day to day life on earth is integrally effected by the seasons and so to transpose the zodiac over the seasons – works. The essential qualities of the signs of the zodiac do line up with the Sun passing through the seasons. For instance, the Sun passing into Aries conveys the qualities of Spring – active, energetic, vigorous creative new life etc.

Likewise, you could take any developmental pattern and transpose the zodiac. One obvious one would be take the 12 year transit return of Jupiter. Each year is like one sign of the zodiac. The first year when Jupiter is transiting over natal Jupiter is new, energetic and expansive in growth like Aries even though the actual Jupiter return may happen to land in another sign. The twelfth year, like Pisces, has qualities of dissolution and death before the rebirth again with the next Jupiter return.

Because the tropical system is a Solar-based system the commonly held opinion is that the tropical system is better at describing the personality and psychological patterns. The Vedic system is often considered to be better at describing the soul nature and predicting actual events because it’s tied to the actual fixed constellations.

This also becomes apparent when we study the popular reference texts of each system. The Vedic texts shed very little light on psychological patterns and emphasize prediction, whereas it’s just the opposite with the Western reference texts.

It's my opinion that you can get an accurate reading, both in terms of psychological interpretation and prediction, using either system. In the final analysis I think that the accuracy of any system, depends more on the clarity of intuion of the astrologer than on the system itself.

Obtain a copy of your Western chart, if you don’t have one already. Make a list of your planets and their degrees as shown below. Subtract the ayanamsha or 23 degrees from each tropical planetary position and the ascendant to get their Sidereal position.

Example Calculations:
Tropical Positions Sidereal Positions
Asc: 11 Gemini – 23 = 18 Taurus
Sun: 14 Scorpio – 23 = 21 Libra
Moon: 10 Virgo – 23 = 17 Leo
Mercury: 28 Libra – 23 = 5 Libra
Venus: 8 Libra – 23 = 15 Virgo
Mars: 25 Capricorn – 23 = 2 Capricorn
Jupiter: 9 Pisces – 23 = 16 Aquarius
Saturn: 24 Aquarius – 23 = 1 Aquarius
North Node: 18 Sagittarius – 23 = 5 Scorpio
South Node: 18 Gemini – 23 = 5 Taurus
(Optional)
Uranus: 24 Leo – 23 = 1 Leo
Neptune: 3 Libra – 23 = 10 Virgo
Pluto: 14 Virgo – 23 = 21 Leo

An easy way to do this in your head, if the planet’s degrees are less than 23 degrees in any given sign, is to add 7 degrees and go back a sign. For example, if a planet is at 11 degrees Gemini then add 7 degrees and go back to Taurus. The Sidereal position would be 18 degrees Taurus.

If you want to get the exact position of the planet down to the minute then get out a calculator and calculate the exact ayanamsha of the year and month you were born.

Use the following dates for the ayanamsha as a starting point:

January 1st 1940 - 23 degrees 01 minutes
January 1st 1950 - 23 degrees 09 minutes
January 1st 1960 - 23 degrees 18 minutes
January 1st 1970 - 23 degrees 26 minutes
January 1st 1980 - 23 degrees 34 minutes

Use these approximate figures:

4 minutes 11 seconds per 5 years
1 minute 40 seconds per 2 years
50 seconds per 1 year
4 seconds per month