Tropical or Sidereal Zodiac? Which one should we use?

Dear NightFall Astrology readers,

We often hear that “we should use the sidereal zodiac because it’s true to the stars”, but this is only half true. In this article, we will examine why that is and why both the tropical and sidereal zodiacs are valid.

You’ll probably discover for the first time (or deepen your understanding of the topic) that there are 3 zodiacs in astrology: the tropical one (which you’re familiar with and is aligned with the equinoxes and the solstices), the fixed Babylonian (sidereal) zodiac, which is based (partially) on constellations, and the actual constellational zodiac.

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But before we get into briefly delineating these 3 zodiacs, let’s define the term “zodiac” first. The zodiac is the apparent path through the sky that the Sun, Moon, and visible planets to the naked eye make. The “road” followed by the Sun, Moon, and classical planets is divided into segments.

It has to be noted that what we know today as the sidereal and tropical zodiacs are idealised/regularised divisions of the 17-18 UNEVEN constellations initially used by the Babylonians. Both the tropical and sidereal zodiacs use 12 equal segments/divisions of the sky.
The main difference lies in their reference points: the sidereal zodiac’s reference point is the fixed stars (of the constellations), and the tropical zodiac’s point of reference is the celestial equator. The tropical reference is the intersection of the ecliptic (solar path) with the equator (Earth path) at the equinoctial points (in the Northern hemisphere).

{ This article Includes translations from Bulgarian & French. }

I. The initial constellational zodiac & early Babylonian astrology:

The earliest account of the constellation zodiac was made in what is still considered today the home of Astrology: Babylon. As mentioned in our intro, the Babylonians had used, in their earliest astrological practice, 17-18 uneven constellations. The Babylonian constellations vary in size and orientation and lack well-defined boundaries, while constellational references may include positions before, in, or after specific constellations. The Moon’s passage through the constellations is more significant than the precise ecliptic as defined by the Sun’s passage. This emphasis on the Moon’s position is evident in the ancient use of Indian nakshatras and Babylonian constellations. Constellations that rise before sunrise were notable.

Early Babylonian astrology can roughly be equated with the astrology of the regions of Babylonia and Assyria prior to the Persian conquest in the mid-6th century B.C. Late Babylonian astrology can be roughly equated with the astrology of the same regions from soon after the Persian conquest until about the 1st century A.D. Early Babylonian astrology was not static. The most important work of Early Babylonian astrology, the MUL.APIN, may represent a stepping stone from Early to Late Babylonian astrology. It continues the tradition of the late 2nd millennium B.C. but with a couple of changes and a strong influence on the later, more mathematical tradition.

The MUL.APIN is an ancient Babylonian astronomical text that dates back to the 7th century B.C. It is one of the earliest known astronomical compendia that provides a comprehensive description of the Babylonian celestial knowledge. The text consists of a collection of observations and descriptions of celestial phenomena, including the positions and movements of stars, planets, and constellations, as well as lunar and solar eclipses.

The MUL.APIN contains detailed instructions on how to use celestial observations to determine the beginning and end of months, seasons, and years, which were essential for the Babylonians’ agricultural and religious practices. It also includes a star catalog with over 1000 stars and their positions relative to specific constellations.

The MUL.APIN is a significant source for understanding the development of Babylonian astronomy and its influence on subsequent astronomical traditions. It is an essential reference for modern scholars of ancient astronomy and the history of science.

Also, the reign of Nabonassar (747-734 B.C.) emphasised keeping systematic astronomical diaries, which enabled the discovery of sidereal periods for planetary phenomena.

The Babylonians dropped the use of this zodiac by the 5th century B.C. as it was highly impractical. Then came the standardised, equally divided sidereal zodiac. It is important to note that the constellational zodiac differs in significant ways from a regularised sidereal zodiac. In a constellational zodiac, the specific stars and constellations confer meaning, not segments and degrees.

II. The sidereal zodiac:

The Babylonians used a 12-month calendar with 30 days in each month for administrative purposes beginning at the close of the fourth millennium B.C. Pre-literate logographic cuneiform accounting texts use this calendar, making it the earliest known written calendar. Through the phases of the fixed stars and variations in the length of the day, this calendar became synchronised with the tropical/seasonal cycle by the end of the second millennium B.C. By the time of the MUL.APIN’s composition (in the 7th century B.C.), it had become the primary calendar for Babylonian astronomy and astrology. It plays a pivotal role in the MUL.APIN, the most widely reproduced Babylonian astrology text.

In our intro, we briefly established that a sidereal zodiac is defined as 12 equal divisions of the constellations with respect to a fixed star. So, in this respect, it isn’t ENTIRELY based on the stars, as it’s an idealised or symbolic division of the initial uneven constellations. 

The original definition of the Babylonian sidereal zodiac is based on the first-magnitude stars, Aldebaran and Antares, located exactly at the midpoint (15 degrees) of their respective signs, Taurus and Scorpio, defining the central axis of the zodiac. This coordinate system of twelve zodiac signs, each 30 degrees long, emerged in Babylonian astronomy during the fifth century B.C. and was transmitted to other civilisations. This system relied on the ecliptic coordinate system of the Babylonian sidereal zodiac and the availability of records of astronomical observations collected over an extended period of time. The introduction of the zodiacal coordinate system into Babylonian astronomy was made possible by the systematic observation of the night sky by Babylonian astronomers over many centuries.

Aldebaran and Antares are 2 of the 4 chief stars that delineate the sidereal zodiac. The other 2 are Regulus (5° Leo) and Fomalhaut (10° Aquarius). 

The sidereal zodiac is intimately related to the old observations of the Moon relative to the images of the constellations (observational omens). It is important to note that there are many sidereal zodiacs, as different reference stars can be used. Still, all sidereal zodiacs are fixed relative to a reference star. For example, the guiding star in the Vedic/Indian system is Chittra (Spica) at 0° Libra, exactly opposite to the Vernal Point – Chittra/Spica is used because there are no first-magnitude stars in Aries itself.

III. Precession of the equinoxes and the birth of the tropical zodiac:

A. The Precession of the equinoxes:

In compiling his famous star catalogue (completed in 129 B.C.), the Greek astronomer Hipparchus noticed that the positions of the stars were shifted systematically from earlier Babylonian (Chaldean) measures. This indicated that it was not the stars that were moving but rather the observing platform—Earth. Such a motion is called precession and consists of a cyclic wobbling in the orientation of Earth’s axis of rotation with a period of 25,772 years.

Precession was the third-discovered motion of Earth, after the far more obvious daily rotation and annual revolution. Precession is caused by the gravitational influence of the Sun and the Moon acting on Earth’s equatorial bulge. To a much lesser extent, the planets exert influence as well.

The precession of the equinoxes is a process whereby the position of the stars and constellations gradually move about the seasons. The precession rate is one degree every 72 years = 0.838 minutes per year or 50.2675 seconds per year.

The popularisation of Claudius Ptolemy’s (the Greek astronomer also known as the “father of astronomy”) work on precession in the 2nd century A.D. obscured Happarchus’s earlier research. Because of this lack of clarity, older astrological texts often overlook the tropical vs sidereal debate.

The first astronomers to become aware of precession made the conscious choice to use a tropical orientation. The Greek tropical zodiac distinguishes itself as the first regularized 12-sign zodiac to be consciously distinguished as tropical or sidereal. The Greek zodiac used the equinoxes and solstices as reference points from the start, in the late 5th century B.C. Then beginning with Hipparchus in the 2nd century B.C. we see the first conscious distinction between tropical and sidereal, with the choice of tropical.

We currently lack evidence that prior to Hipparchus and Ptolemy, astronomers or astrologers were aware of precession and choosing a sidereal orientation for a regularised zodiac. Therefore, the unconscious sidereal fixity of the Babylonian zodiac, which started in the 5th century B.C., should be contrasted with the conscious tropical fixity of the zodiac of the Greek astronomers later in that same century.

As a result of this decision to use the tropical zodiac of the seasons rather than the sidereal zodiac of the constellations, the zodiac used by most western astrologers is no longer associated with the constellations or the fixed stars. Thus, the two zodiacs at this point differ by roughly 24 degrees, which is almost one full sign, although not quite. So, a planet at 24 Aries in the tropical zodiac would be somewhere around zero degrees Aries in the sidereal zodiac.

B. The Tropical Zodiac:

As we established in section A., the Greeks already used the equinoxes and solstices as reference points from the start, in the late 5th century B.C., but the first conscious distinction between the sidereal and tropical zodiacs was made in the 2nd century B.C. and officialised and popularised by Ptolemy in the 2nd century A.D. Most of the things that we associate with astrology, including many of the characteristics of the signs of the zodiac, originated during this time.

This remains today the most commonly used zodiac in the West for the past 1,800 years. So, what’s the tropical zodiac?

During the 1st-2nd centuries B.C., the seasons were aligned with the sidereal zodiac in such a way that the start of the seasons coincided with the beginning of cardinal signs, namely Aries, Cancer, Libra, and Capricorn. The middle of the seasons matched up with the fixed signs: Taurus, Leo, Scorpio, and Aquarius, while the end of the seasons coincided with the mutable signs: Gemini, Virgo, Sagittarius, and Pisces.

This alignment was significant because astrologers made symbolic connections between the nature of the seasons and the meaning of specific signs. For example, the cardinal signs were associated with the initiation of new activities and changes. In contrast, the fixed signs represented the stabilisation of existing activities, and the mutable signs symbolised transitions. This relationship between the seasons and zodiac signs is the foundation of the tropical zodiac, which is measured relative to the seasons, starting at the vernal equinox.

The 3 zodiacs can be summarised through the following diagram:

• The inner wheel shows the tropical zodiac, which is aligned with the equinoxes and the solstices.
• The middle wheel shows the sidereal zodiac, which is roughly aligned with the constellations, being about 24 degrees off of the tropical zodiac at this point.
• The outer ring is a really rough sketch of the constellations that fall on the ecliptic, just to give you an idea of how they vary in size.

III. Which zodiac should we use: the Tropical or Sidereal one?

Before answering this question, a couple of historical and cultural remarks must be made.

(i) The sidereal zodiac remains mainly used in India and by Indian/Vedic astrologers, but the sidereal zodiac isn’t Indian per se, as we’ve demonstrated earlier in this article. Vedic astrology has its own separate philosophy, cosmology, and mythology, which are very different from Western ones and mainly based on the Vedas (Sanskrit: वेदः, lit. ’knowledge’), which are a large body of religious texts originating in ancient India. Composed in Vedic Sanskrit, the texts constitute the oldest layer of Sanskrit literature and the oldest scriptures of Hinduism.

(ii) However, some Western astrologers started using the sidereal zodiac again in the mid-20th century (the 1940s) thanks to the works of Irish astrologer Cyril Fagan. This ended up in the rediscovery and study of Babylonian astrology, which was popularised by notable astrologers such as Kenneth Bowser and Rumen Kolev.

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(iii) French Astrologer, Patrice Bouriche, has interestingly demonstrated in his book ” L’histoire secrète de l’astrologie (the secret history of astrology)”, published in 2015, that most Western and Arabic astrologers (most notably Rhetorius and Masha’allah) were using the sidereal zodiac until the 8th century A.D.

(iv) In both sidereal and tropical astrology, there are 12 signs of the zodiac, not 13. The sidereal zodiac is an energy mandala oriented to the fixed stars, not a literal map of the modern constellations. Astrologers have always known the constellation Ophiuchus cuts into the ecliptic plane and integrated its Serpent-Bearer symbolism into the zodiac sign of Scorpio. There are 12 signs by definition of every culture that has ever used the zodiac: Babylonian, Egyptian, Persian, Greek, Roman, and Indian. 

Now comes the perennial question, which zodiac should we trust/use?

The answer is both. The sidereal zodiac is used for the evolution of humanity over thousands of years (what we call “ages”, “eras”, or “epochs” in astrology, such as the age of Aquarius that is already upon us). The cyclic wobbling in the orientation of Earth’s axis of rotation (precession) has a period of 25,772 years.
This means that the constellation rising on the Eastern horizon on the spring equinox changes every 2,160 years.

This zodiac, as previously stated, is more suitable for the analysis of the evolution of the human soul and humanity at large (mundane astrology). It’s an archetypal zodiac.
So, the longer the cycle, the harder it is to apply to the average human lifespan (70-80 years in current times).

Whereas a tropical cycle, based on the tropical zodiac, lasts a “human year” (what we’re usually accustomed to in our own Gregorian calendar, and don’t forget that every zodiac is a celestial calendar). Similarly, we all experience sunrise and sunset alongside the changing of the seasons.

However, how many of us today can say that they were present when the constellation Pisces first rose on the spring equinox above Jerusalem (interestingly enough, not too far from Jerusalem, in the Mesopotamian of Nippur – current-day Nuffar in Iraq, was where the first birth chart was cast and dated: April 24th, 410 B.C. using the sidereal zodiac) when the Pisces age and our calendar switched to A.D. after Christ’s birth? None. Maybe we were there many incarnations ago.

Hence, the sidereal zodiac’s utility for analysing a soul’s evolutionary journey. Yes, I’ve said it; this isn’t your typical modern evolutionary/psychological astrology that you may be familiar with. It goes way beyond that.

But, for this lifetime, the tropical zodiac provides a more concrete understanding of one’s psychological portrait, fate, and events in one’s personal life. Some astrologers also say that the Tropical Zodiac represents the characteristics of the mental and astral/emotional bodies.

The fixed Babylonian zodiac is about 24° degrees behind the tropical one. Meaning if you’re a 16° Aries Sun in the fixed Babylonian Sidereal Zodiac, you’ll be about 22° Pisces Sun in the Tropical Zodiac.

This doesn’t mean that your Sun (or another planet in your birth chart) sign has changed; it simply means that we’re using 2 different systems rooted in 2 different points of reference.
In some rare cases, some people have the same sidereal sign as their tropical one, and Babylonian degrees overlap in the 6° that are still common to both zodiacs for every sign. These are considered blessed/lucky placements.

References and further reading:

• Bouriche Patrice, “L’histoire secrète de l’astrologie – Tome II (L’hérésie tropicaliste venue du Khorassan)”, Autres Talents, 2015.
• Holden James, “A History of Horoscopic Astrology”, M.A., F.A.F.A., 2006.
• Kolev Rumen, “Hermes on the Fixed Stars, First-time translation from the Vienna manuscript Codex Latinus 3124″, 2013.
• Powell Robert, “History of the Zodiac”, Sophia Academic Press, 2007.
• Stoychev Kiril (Bulgarian astrologer, RIP 1970-2021), 2019 lecture about the tropical and sidereal zodiacs.

Thank you for reading.

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