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The Fallacy of the Sidereal vs. Tropical "Zodiacs" Debate

There are several traditions or schools of thought pertaining to Astrology in the world. The most spread out forms are Western Astrology and Indian Astrology. While both of these systems have a lot in common, they generally disagree on one thing, the definition of the 12 Zodiac signs.

This disagreement gives rise to Sidereal and Tropical astrology.

If you are an astrologer, reading the points raised in this article may possibly change you perspective of this debate

Building Blocks

In order to understand the basic logic layed out in this article there are a few concepts that need to be understood:
The Ecliptic This is a 360° celestial plane which tracks the apparent movement of the Sun through the 12 constellations. In reality it is actually the orbital path of the Earth around the Sun. The ecliptic is slightly different on other planets and moons in our solar system as they follow their unique orbit around the Sun.
Celestial EquatorThis is also known as the equatorial plane.
This is the projection of the equator of Earth onto outer space.
The celestial equator can be radically different on other bodies in the solar system and it is never exactly the same as on Earth.
Axial PrecessionThis is also known as axial wobble, because it indicates a somewhat gyroscopic wobble of the axis of Earth in a semicircle defined by the axial tilt of Earth.
This precession makes the celestial equatorial plane wobble and move along the ecliptic, which is called the precession of the equinoxes.
Again all the planets and moons in the solar system have their own unique angle and speed of axial precession.


The sidereal zodiac depends on the “fixed” stars. Well, these stars are not entirely fixed, but their movements are so slow it is hardly noticeable in a human lifetime.

The sidereal zodiac is anchored to one or many of these “fixed” stars. But there is no universally accepted sidereal zodiac because astrologers do not agree which “fixed” star should be anchored to decide the beginning of the zodiac. 

Indian astrology predictionsIn contrast, the Tropical “zodiac” is a nodal based system. Its construction depends on the intersection points of two planes, the celestial equator, which is the projection of Earth’s equator projected on outer space, and the path of the Sun, the ecliptic.
In that way, it is similar to the Ascendant (Lagna) which is an intersection node of the ecliptic and the horizontal plane.

Due to the axial precession or wobble of Earth’s axis, the Topocentric “zodiac” (0° in the initial sign Aries) precesses through all the sidereal constellations in roughly 26,000 years, or about 1° every 72 years.

The Tropical “zodiac” is perfectly aligned with the seasons on Earth. The spring equinox (0° Tropical Aries) happens when the Sun is exactly parallel to the celestial equator of Earth when it shines evenly on both hemispheres.


One thing is clear: The sidereal zodiac can be used in outer space and on all the planets and moons in the solar system. You can make an astrological chart from any location on the Moon, Mars, or even Pluto and with the sidereal zodiac, you would be referring to generally the same space in the sky in each case. By using the word space here, we mean relative to known stars and galaxies.

The Tropical “sign” system, on the other hand, only applies to the celestial body that we are on. The axial tilt and the axial wobble of this body decide where the celestial equator of the body intersects to the ecliptic of the Sun. 

And here is the perturbing facts:
There are situations where the Tropical “zodiac” doesn’t exist as the substance of it’s calculation is simply not there:

  1. There may be celestial bodies out there from which the Tropical zodiac cannot be calculated. If the planet’s celestial equator is perpendicular with the ecliptic, then there is no way to construct the Tropical zodiac, as there is no venereal equinox.
  2. The Moon and Venus are both very close to this situation as their axial tilt is very low, with their celestial equator closely aligned with the ecliptic.

In outer space, there is no Tropical zodiac at all, in the absence of a celestial equator.

There are a couple of more angles to this problem.

The current Tropical 0° of Aries on the surface of Mars is currently found at roughly 29° in the Sidereal Scorpio. This means that the Tropical Aries, on Mars, covers most of the constellation of Sagittarius. Since the axial tilt is different on all the planets, the corresponding Tropical “zodiacs” will have different start points on every single planet and moon. There is no universal Tropical “zodiac”. It is a local thing.

Furthermore, the rate of axial precession (the wobble of the axis) is very different on all celestial bodies. An extreme case of this is our own Moon. Its axial wobble takes only 18.6 years, which means that the Tropical 0° Aries on the Moon moves 360° through all the constellations every 18.6 years!

Conclusion: The Tropical “zodiac” is bound to a celestial body and the Tropical zodiac that we know today is directly linked to the current axial tilt of Earth.

In other words: The Tropical division makes more sense when viewing the celestial sky from the point of view of the surface of the earth. The Sidereal zodiac, on the other hand makes more sense from any point in our solar-system.

The Sidereal Zodiac may be more universal than the Tropical one, but could this mean that the Tropical one is more local in its significance?

Are we comparing apples and oranges?

Yes, when debating which system is “true” and which one is “false” we forget that we are comparing entirely different things.

These systems have been confused with each other since about 200 BCA at which time they were aligned on Earth. At that time the start point of the Sidereal zodiac was the same as the starting point of the Tropical one. And at that time no astrologer was bothered with the question which one was the right one.

The question: “which zodiac is correct?” has always been the wrong question, because we have never been speaking about the same phenomena.

My Conclusion

In this article, I have pointed out facts that are never discussed in the debate between the schools of Tropical and Sidereal Astrology. When these two systems are seen for what they really represent there is nothing to debate about because they are simply not the same thing.

During my pondering on this for over twenty years I have formulated a theory of how these two systems work in harmony:

  • The Tropical system is the collective house system of planet Earth. It makes sense to me because modern Tropical astrology is generally more concerned with personality and psychological topics.
  • The Sidereal system is more concerned with universal energy and therefore the dignities of the celestial bodies seems to work better using the Sidereal Zodiac. It is also more concerned with measurable and concrete outcomes than the Tropical system.

These two systems can in this way be used together. There is no need to reject either one. Quite possibly using them as separate protocols can supplement and deepen our understanding of Astrology.

The golden age of Astrology is coming. This means that more empirical and scientific studies will be conducted in a more accurate and precise way than before. The scientific validation of astrology is inevitable. Perhaps I am over-optimistic, but I think as early as 50 to a 100 years from now Astrology will be firmly accepted in the scientific paradigm.

But in our efforts to formulate the necessary scientific approach we need to understand the variables of the system.

The information that I have presented here is a step towards that understanding.