Why Use the Tropical Zodiac?

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Table of Contents

Introduction: Contentious Choices

The practice of astrology is riddled with contentious choices. Which one of the dozens of house systems should you use? Do chart factors essentially represent psychological or general real-life circumstances? Does astrology work according to a physical cause, for instance related to some ill-understood element of quantum mechanics? Or is it maybe linguistic, pertaining to a rational faculty of the cosmos which provides signs? Or could it be something else entirely?

Some issues can be resolved without much effort. Sometimes all that is needed is an open mind, a little chart work, and a brief exploration of astrology’s history and internal logic. However, other issues are more difficult. These issues can require a thorough familiarity with the principles of delineation and years of experience from hundreds of charts. Similarly, there are times when a superficial understanding of astrology’s history does not suffice and we have to deeply analyze particulars.

House System

I consider the choice of house system to be one of the easier issues to resolve, despite continued confusion in this area. Whole sign houses are the only house system that was used for topics in the first centuries of Hellenistic astrology (i.e. when the system came about). It also fits with the internal logic of the astrological system. The house issue is not a difficult one to address with some history, understanding of astrological principles, and work with chart examples. I’ve addressed the house issue at length, from multiple angles, in my article on the houses. Still, it continues to be one of the most vexing choices for beginners in astrology.

The Zodiac

Some contentious issues are more difficult to resolve. Among the most difficult and contentious is the matter of the zodiac. After more than 7 years of writing articles for Seven Stars Astrology, I’m still confronted by angry readers who attempt to convince me that I’ve made a grave error: I’m using the wrong zodiac!

I’ll explore the historical issues in more depth and with reference to relevant scholarship in the latter part of the article. However, before proceeding I’d like to briefly touch upon the main issues. The Babylonians created the zodiac as a means of measuring positions on the ecliptic. It was also intended to correlate their 12 month calendar, which began near the vernal equinox, with the twelve unequal constellations crossing the ecliptic. They do not appears to have known that the stars and calendar were actually drifting slowly away from each other and so they set the vernal equinox at a specific degree (at 8° or 10° Aries).

The Division

Knowledge of precession, the shift of the stars relative to the equinoxes, was taken two different ways in Indian astrology and western astrology. Indian astrologers accounted for the shift by arguing for various reference stars which could be used to keep the zodiac fixed with regards to its position relative to the constellations (sidereal zodiac) reflecting the original Babylonian intention and focus on the sidereal year. Western astrologers settled on a long-running Greek practice (from the late 5th century BCE) of starting the zodiac with the vernal equinox (tropical zodiac), fixing it to the calendar and seasonal cycle.

The Losers and The Losers

The sidereal zodiac can be accused of no longer coinciding with the calendar and seasons as the zodiac was intended. The tropical zodiac can be accused of no longer coinciding with the constellations for which the signs were named as was intended.

On only one issue did they agree, that the Babylonian standards were not sufficient. No one demonstrating knowledge of precession advocated to keep the zodiac fixed in such a way that the vernal equinox would always occur at 8° or 10° Aries.

The Babylonian Zodiac is Not Simply a Sidereal Zodiac

We should collectively refer to the two competing standards used by the Babylonians (from Systems A and B; vernal equinox at 10° or 8° Aries respectively), as “the Babylonian zodiac”. This serves to distinguish them from a tropical zodiac (vernal equinox at 0 Aries) and modern sidereal zodiac (distance to some explicit reference star determines 0° Aries).

The labeling of the Babylonian zodiac as “sidereal” accords with its original form and also with the Babylonian focus on sidereal periods and the constellations for observed phenomena. However, it was originally intended to be fixed with respect to both the stars (sidereal) and the calendar/equinox (equinox at 8° or 10° Aries). Additionally, it is not clear that all later adopters of the Babylonian zodiac used it sidereally (i.e. with respect to updated sidereal tables) vs. tropically (i.e. computing longitude relative to an 8° equinox). Referring to it simply as a sidereal zodiac confuses the Babylonian zodiac with today’s sidereal zodiacs (such as Lahiri or Fagan-Bradley). In such a way it obfuscates the circumstances of its development and subsequent history.

Hellenistic Context

The zodiac choice is particularly complex in the context of Hellenistic astrology. The zodiac was borrowed from the Babylonians but new Hellenistic doctrines, including sign associations, arose at a time when sidereal and tropical zodiacs nearly coincided. Sign qualities in the Hellenistic period pertained to the seasonal calendar as well as the images of the constellations. Furthermore, some Hellenistic astrologers, ignorant of precession, including Thrasyllus and Vettius Valens, used the Babylonian zodiac, sometimes even into the 4th century CE. Meanwhile, Claudius Ptolemy of the 2nd century CE, cognizant of precession, set the stage for the widespread adoption of the tropical zodiac.

The Babylonian Zodiac was No Longer “Sidereal” in the 1st and 2nd Centuries CE

Astrologers using the Babylonian zodiac apparently thought they were using one that was both sidereal (fixed to the stars) and tropical (fixed with respect to the position of the equinox), due to their ignorance regarding precession. As noted, this Babylonian zodiac had not been adjusted for precession (the shifting of the stars relative to the equinox) so it had actually lost its original correspondence with the stars. Further complicating matters, the late 2nd century was a time when the tropical and sidereal zodiacs coincided to about a degree of accuracy. Therefore, the Babylonian zodiac used by some early Hellenistic astrologers was much farther removed from the original and modern sidereal zodiacs than the tropical zodiac was in the same period. See Part III for details regarding this.

Two Zodiacs at the Same Time?

If you’ve read my article on the signs, you’ll know that at times I’ve felt that the sidereal zodiac may have a place in Hellenistic astrology. Since some sign associations pertain to the constellations, I’ve flirted with the idea of using a sidereal zodiac just for those indications. However, in recent years I’ve become less certain that using two zodiacs for western astrology will ever make sense. I believe that the tropical zodiac is the system of signs for western astrology, and that for a deeper dive into constellational symbolism, we should use the constellations themselves, not the sidereal zodiac.

With that said, I in no way imply that the tropical zodiac is more effective for Indian techniques. I cannot speak to that topic due to my lack of experience with Indian astrology. However, when it comes to the use of signs and their key features for traditional western astrology, including Hellenistic astrology, I find the tropical zodiac much more effective.

13 Signs?

I want to make a quick note about a further complicating factor. Unfortunately, there are popular astronomers putting out articles that confuse the notions of sign and constellation. These astronomers, who should know better, chide astrologers who “foolishly” use 12 signs when in fact 13 constellations cross the ecliptic. However, astrologers from even before the advent of Hellenistic astrology recognized the zodiac as 12 equal divisions of the 360 degree circle, not the 12 constellations from which they were named. Twelve is important not because of the number of constellations crossing the ecliptic but because there were 12 months in the lunisolar calendar. The division of the ecliptic into 12 signs followed from the calendar of 12 months, not from some long-standing tradition of using 12 constellations. The Babylonian tradition was actually to use 17-18 zodiacal constellations.

Divisions of time and circles into 360 degrees, 60 minutes, 60 seconds, 12 segments, and so forth should be familiar to anyone who has used a clock and a compass. These divisions originate from the Babylonians who came up with the zodiac and used a sexagesimal (base 60) number system. Signs are equal symbolic units of space-time, not the unequal constellations of stars. The initial importance of 12 came not from a number of constellations in the sky, but from the number of lunar months in the solar year. There are 12 New Moons in a given year. 360 is also interesting as it is the mean number of days between the mean solar year of approx. 365.24 days and the mean lunar year of approx. 354.37 days. The mean between the solar and lunar years is approx. 359.8 days, almost exactly 360 days.

Argument Structure

My rationale for using the tropical zodiac has always been primarily empirical. In other words, I find that the tropical zodiac works better for Hellenistic astrology. I don’t mean it works better in some amorphous, personal, “works better for me” sort of way. Given years of experience with applying Hellenistic techniques, I’m equipped to provide concrete examples of why the best results come with the tropical zodiac. As the empirical matter has been the most important matter to me, I present it first.

Historical matters are more complicated and can be quite confusing. A thorough understanding of the history is very important. I believe that logic and zodiacal history also support the use of a tropical zodiac. After I present my empirical examples, I examine some of the historical and logical facets of my decision. Those who want to dig into the nitty-gritty of the logic or history first can skip to Part II or III respectively. I conclude with my own story about how the tropical zodiac was responsible for turning me from a skeptic to an astrologer in the first place.

Part I: Example Charts

The following 7 examples illustrate the superiority of the tropical zodiac from an empirical standpoint for early traditional western principles and techniques. As the Fagan-Bradley ayanamsha is typically the one used by western siderealists, I will adopt that one in the sidereal charts of this article.

Ex. 1: Jimi Hendrix

I’ve previously pointed out that Hendrix’s chart works best with whole sign houses and a tropical zodiac. I addressed his chart at length in the article on the houses and also looked at it in terms of professional indications. See his chart below (natal chart of Jimi Hendrix, AA-rated).

Hendrix - twelfth-parts
Hendrix’s Tropical Birth Chart with twelfth-parts (outside wheel)
Hendrix - Sidereal FB with twelfth-parts
Hendrix’s Sidereal Natal Chart with twelfth-parts (outside wheel)

Career Indicator: Mercury-Venus Tropical; Mars Sidereal

Per Hellenistic techniques, the planets relevant to actions (i.e. career; skill-development; occupation) are Mercury, Venus, and Mars. We look to see if they are in eligible places. The planets that are most relevant are in the best of those places and/or have some additional special indications (e.g. phasis, station). I’ve discussed the technique in a prior article and have noted that I tend to follow Paulus Alexandrinus (4th century CE). Please review that article for details on the Hellenistic approach to this topic.

Tropical – Mercury-Venus and the Sun in the 1st

Mercury and Venus (as well as the Sun) are in the 1st house in the tropical chart. This makes them relevant as planets of actions, and also relevant for the identity and temperament. As I’ve noted, Mercury pertains to complexity, speech, composition, writing, and manual dexterity while Venus pertains to the arts, drugs, sexuality, and physical pleasure. One indication of Mercury with Venus is musical composition. Guitar playing is particularly relevant as stringed instruments played with one’s fingers are under the domain of Mercury (digits) and Venus (music).

Hendrix - twelfth-parts

Mercury, Venus, and the Sun are all in the bound and sign of Jupiter, the sect benefic, connecting them with fortune. The twelfth-part of Jupiter is the 5th house of the chart, the Joy of Venus, which can pertain to the fruits of one’s labor and to material benefit (it is the house of good fortune). The twelfth-part of Mercury is in the 2nd house in the Mercury bound, connecting it with income, while that of Venus is in exaltation in the 4th. Both the 2nd and 4th are also eligible places, further emphasizing the importance of Mercury-Venus for the career.

Sidereal – Mars in the 11th

The sidereal chart still has Sagittarius rising and still has a Moon-Jupiter conjunction in Cancer, the 8th house. However, the career indications are completely different. Mercury and Venus are now in the 12th house. They are no longer in an eligible place for actions. They no longer pertain to the identity or character either as they are not in the 1st and do not rule the 1st house in any way. Now they are in the 12th house of the Bad Spirit, pertaining to secret enemies, imprisonment, and social ills. Mars is the clear planet of actions, as it is in the 11th place and has its twelfth-part in the 8th, both of them being eligible places. It also has its twelfth-part closely conjunct Jupiter’s twelfth-part, with the Moon and Jupiter in the 8th.

Hendrix - Sidereal FB with twelfth-parts


Mars is insufficient here as an answer. Yes, Hendrix was in the army for a time, but Mars was not the operative planet for his actions, skill-development, and occupation. Hendrix is not known for his manual labor, his competitive leadership, his political acumen, brawn, ferocity, or military prowess. Hendrix is known for his rich dexterity and complex compositions, his guitar playing, his singing, and his identity itself. All of those fall under the purview of a Mercury-Sun-Venus conjunction in the Jupiter bound of Sagittarius in the 1st house. The sidereal zodiac falls woefully short here when looking at Hendrix’s career and character.

Ex. 2: OJ Simpson

In this second example, I look at another chart I’ve addressed previously in terms of profession. In a prior article, I noted how the Hellenistic technique for professional significator correctly indicates Mars for OJ Simpson. His chart is birth information is rated AA for accuracy. To keep things brief, I refer you to my article for details on the analysis. Let’s see what the indications are when using the technique with the sidereal zodiac.

Tropical – Actions: Mars in XI; tpMars in I; Mars rules Asc bound

Mercury and Venus are in XII so are not particularly relevant for profession. Mars is in XI which is a relevant place and Mars advances toward the MC. Significantly, Mars rules the bound of the Ascendant, has triplicity at X and the MC, and its twelfth-part is in the 1st house. The twelfth-parts of Venus and Mercury are in XII and IX respectively, emphasizing that they are not as significant for actions. Therefore, we see lots of reinforcement to Mars as significator of actions, and also that it is relevant for character. Mars is in the fortunate 11th house, with twelfth-part Jupiter and in Jupiter’s bound, while Jupiter is ruled by Mars, connecting immense fortune to Mars (athletic star).

OJ Simpson Natal
Simpson’s Tropical Natal Chart with twelfth-parts (outside wheel)

Tropical – Character pertains to XII, Saturn, Mars

Additionally, let’s look at some indications about character and life circumstances. The Sun which rules the 1st is in the 12th, one of the dark or bad places. This connects the character with the 12th house and its themes of undoing, imprisonment, and secret harm. Mercury, also relevant for character and intentions is additionally in the 12th. Both Venus and her twelfth-part are in the 12th, connecting her strongly to the themes of undoing, imprisonment, and secret harm. Furthermore, Saturn is in the 1st house of self as is the twelfth-part of Mars, indicating that both malefics are operative in the house of the self and character. See this article for more analysis of the character indications in OJ’s chart.

Sidereal – Actions: Mars in X and Ruling MC

Mars is also the professional indicator using the sidereal zodiac. In fact, its relevance for profession is just as striking. Mars is in X and rules the MC. However, what is lacking is a connection between Mars and self-identification. Mars has no rulership at the Ascendant and its twelfth-part is not in the 1st or a stake. Additionally, Mars is missing the Jupiter connection. Mars is not ruled in any way by Jupiter, is not with Jupiter’s twelfth-part, and Jupiter is not in a sign of Mars. We get Mars as career significator but not as relevant to the character nor necessarily associated with luck or fortune.

OJ Simpson Sidereal FB Natal
Simpson’s Sidereal Natal Chart with twelfth-parts (outside wheel)

Sidereal – Character pertains to Sun and Venus in XI and Jupiter in III

Most strikingly, the malefic connections to character are largely absent in the sidereal chart. The character is dominated by the Sun which is in the fortunate 11th house and with the benefic Venus. Venus also has her twelfth-part in the 1st. This suggests a very solar and Venusian character. Jupiter rules the bound of the Ascendant and Jupiter is in Libra, a house of Venus. The twelfth-part of the Ascendant is also ruled by Venus (by bound). Again, we are getting the sense of a very magnanimous and positive individual with a sweet artistic or feminine temperament. Gone are the negative associations with Venus, the malefics in the 1st house, the ruler of the 1st in XII, and the identification with the out of sect Mars. These are not trivial losses when it comes to character delineation.

Ex. 3: Whitney Houston

I have also previously examined Whitney Houston’s chart. I’ve addressed the factors pertaining to her death in a prior article that explores her chart in some depth, as well as an article on the primary directions at the time of death. Whitney Houston’s birth information is Rodden-rated AA for accuracy.

Tropical – Venus-Mercury Actions; Venus-Jupiter Attended by Difficulties for Character

Whitney Houston’s tropical chart has the Venus bound of Pisces rising. Venus (arts) is in the 6th (a relevant place to actions) and her twelfth-part is in the 10th (actions) in her own bound of Sagittarius. Mercury (vocals) is also prominent for actions, being in Virgo (exaltation), the 7th house, in the bound of Venus. Mercury’s twelfth-part in its own bound of the 11th house of Good Spirit.

Therefore, Venus and Mercury prevail in the chart when it comes to actions. They are connected with fortune (Jupiter and XI) as well as brilliance and acclaim (Sun and X).

The character is particularly jovial and venusian (Pisces). However, it is also marked by some of the more troublesome manifestations of both (over-indulgence, escapism, pleasure-seeking) as they are both in dark places and afflicted by malefics.

Houston with Twelfth-Parts
Whitney Houston’s Tropical Natal Chart with twelfth-parts (outside wheel)

Sidereal – Mercurial Actions; Saturn-Mercury Character

In the sidereal zodiac, Houston’s Ascendant changes to Aquarius. It goes from a mutable water sign ruled by benefics (pleasant character but unstable or vacillating and putting a premium on the subjective) to a fixed air sign ruled by Saturn (cooler temperament, serious, idea-oriented, stubborn). The twelfth-part of Mercury in the 1st house further emphasizes and intellectualism. The twelfth-part of Mars in the 1st shows a hot competitiveness. Venus has no rulership of the 1st.

Mercury is the most important planet for actions, as its twelfth-part in the 1st reinforces its advancing position in the 7th. Mercury has the strongest connections to to actions (and the personality) of the 3 planets of actions. Saturn’s twelfth-part is in the 10th, so overall we see a particularly Mercury-Saturn orientation for career and personality. She could possibly be an appraiser or tax assessor. Venus is relevant for actions but she has only triplicity at X, no rulership at I, and a twelfth-part in XII. Therefore, Venus is much less relevant than Mercury.


In short, the character and career indications for Houston are very different in the sidereal zodiac and much less compelling. Note that some of the predictive examples I gave in my other articles also don’t hold because of the different house and rulership arrangements.

Whitney Houston FB Sidereal Natal
Whitney Houston’s Sidereal Natal Chart with twelfth-parts (outside wheel)

Death and Directions

Directing through the bounds is a zodiac-dependent predictive technique. It is one of the oldest and most popular uses of primary directions. I have noted in past articles the importance of the Sun-Saturn opposition in the timing of Houston’s death at age 48. It was activated by planetary years, profections, and more. I have also looked at the death in terms of primary directions, including those through the bounds of the tropical zodiac.

Tropical Distributor: Ascendant -> Saturn

The distributor of the Ascendant, pertaining to personal circumstances, during the period of her death (on Feb. 11, 2012) was Saturn. It would have been followed by a Mars period. The two final malefic bounds was considered particularly challenging. Saturn as distributor is particularly relevant given the other predictive indications concerning Saturn at death.

Houston Distributors Tropical
Houston’s Tropical Ascendant Distributors – Death at Age 48
Sidereal Distributor: Ascendant -> Venus

By contrast, the distributor of the Ascendant in the sidereal zodiac is Venus. This fails to adequately capture the role of Saturn in the death.

Houston Ascendant Distributors Sidereal
Houston’s Sidereal Ascendant Distributors – Death at Age 48

Ex. 4: Karl Marx

I’ve previously addressed Karl Marx’s natal chart in terms of career, character, atheism, and some additional topics. Please see my article on him. The birth time of Karl Marx is from his official birth record (given a Rodden Rating of AA for accuracy). His rising sign is Aquarius in both tropical and sidereal astrology. Therefore, Saturn rules the 1st house either way. However, every planet except Venus occupies a different house of the chart sidereally than tropically. Therefore, the zodiac choice largely determines their topical associations.

Tropical – Focus on Money’s Dark Side

The Ascendant lord, Saturn, is in II, the house of money. This puts a personal focus on identifying with this out of sect Saturn in the house of money. Additionally, the bound of Mars rises and the twelfth-part of Mars is also in II, reinforcing the aforesaid indication. Mars itself is in the 6th of labor. Additionally, Jupiter rules the 2nd and naturally rules money (and spirituality), and Jupiter is in the 12, a dark place, ruled by Saturn. Therefore, we see a personal focus on money matters (2nd and Jupiter) with strongly malefic associations.

I noted this strong back and forth relationship between Jupiter and Saturn over money matters in my article on Marx. Another consequence of Jupiter in the 12th and malefics in a sign of Jupiter is the lack of spiritual faith. However, the identification with Saturn in both tropical and sidereal charts tends toward doubt anyway.

Karl Marx twelfth parts
Karl Marx’s Tropical Natal Chart with twelfth-parts (outside wheel)

Sidereal – Focus on Self and Career but Positive Money Associations

In the sidereal chart there is a still a strong identification with Saturn, as well as Mercury. Saturn is in the 1st house, as is the twelfth-part of the Ascendant. Therefore, there is a strong emphasis on the self, body, or identity, and difficulty associated with these things (out of sect Saturn).

As in the tropical chart, there is an association between friends and benefits (11th ruled by Jupiter). However, in the sidereal chart we find immense positive indication regarding Jupiter in terms of both natural significations and those concerning money. Jupiter is in its joy in the 11th, with the twelfth-part of the Sun, and dominating the 2nd house which it rules. Jupiter’s twelfth-part is in the 7th house, signifying fortune in partnership.

Identification is still primarily with Saturn and Mercury so we wouldn’t necessarily expect spiritual faith. However, Mars no longer dominates the 9th and Jupiter is overall more benefic, so it less pronounced.

Money Matters

We especially wouldn’t expect negative associations with money. The house of money is brimming with positive indications in Marx’s sidereal chart. Marx was notoriously critical of the wealthy and capitalism in his lifetime and notoriously bad with money. He actually lived in very impoverished circumstances through much of his later life despite a wealthy upbringing and frequent loans from wealthy friends. The sidereal chart doesn’t adequately capture these facets of his life.

Karl Marx FB Sidereal Natal
Karl Marx’s Sidereal Natal Chart with twelfth-parts (outside wheel)

Note on Twelfth-Parts

As we are more than halfway through the chart examples, I want to point out something about the efficacy of the twelfth-parts. I have noted previously the importance of the twelfth-parts. On the site, they have been used them in a variety of contexts to show that they are useful in all chart work. Interestingly, I’ve also pointed out that the twelfth-parts are almost as old as the zodiac itself, being used in Babylonian astrology prior to their use in Hellenistic astrology. A couple readers have questioned the use of the twelfth-parts with the tropical zodiac given that they were initially used with the Babylonian zodiac.

In the chart examples, I have consistently shown how the tropical zodiac and its twelfth-parts provide superior information when compared with the sidereal chart and its twelfth-parts. Hellenistic and medieval astrologers who used the tropical zodiac extolled the virtues of the twelfth-parts. On empirical grounds alone, they are a necessity for accurate chart work.

Divisions of Space-Time Not of Stars or Seasons

The twelfth-parts are a symbolic division much like the zodiac itself. The zodiac was not designed to exactly correspond to the constellations of stars nor to the seasons, but to roughly correlate both (see Part III). It corresponds to regular periods of space-time which have associations derived from the constellations and seasons roughly coinciding with them at its inception. The division of the ecliptic circle into 12 equal signs and the division of those signs into a micro zodiac of 12 equal signs are not dependent on either constellations or seasons as a basis. Constellations vary dramatically in size and seasons vary by locale. Conceptually, the twelfth-parts, as microcosmic divisions, fit equally well in either zodiac.


It is similar with the bounds. In recent decades, it has become clear that the so-called Egyptian bounds are actually of Babylonian origin. The bounds are also symbolic divisions of the zodiac. They are not dependent upon or based upon star clusters, nor on subdivision of the seasonal calendar. As signs are houses, bounds are like rooms. Each of the five non-luminaries rules a bound in each sign with a malefic always ruling the final bound. Additionally, each planet rules the same number of degrees as its Greater Years. Despite the fact that the logic behind the exact assignment of bounds has been lost, there appear to be some other internal consistencies to the bound ordering. A rationale based on specific stars of the natures of the bound rulers, akin to Indian Nakshatras, has not been argued.

Ex. 5: Dalai Lama XIV

I’m going to switch gears and look at a couple religious charts. I’ve previously analyzed 12 charts in terms of religious belief, using Hellenistic principles, working toward a special technique. One of the most important things noted when it comes to skepticism is identification with Mercury and/or Saturn, as well as unpleasant associations with Jupiter. On the other hand, religious charts tend to have Jupiter prominent in some way, some identification with Jupiter, and some strong connections between self and 9th house matters.

While a Saturnine 9th house associates religion with weight, burden, obligation, and even exile. we have found that with religious leaders it is not that unusual if it also has strong ties to the self and Jupiter. I’ve previously analyzed the Dalai Lama’s chart in this regard.

Note on Questionable Birth Data

The Dalai Lama’s birth information had been given a Rodden Rating of A (from biographical account) at the time that the initial article on him was written. However, it has been revised to a C rating more recently due to some conflicting accounts. Therefore, caution should be taken with the chart and this example can be skipped by those who disregard C-rated data.

Tropical – Strong Jupiter Water Emphasis connected to Self and 9th House

The Dalai Lama has a tricky chart for belief because of the position of Saturn, planet of doubt, in the 9th house (both tropically and sidereally). Also, the Moon applies an opposition to Saturn. However, in the tropical chart we see Jupiter playing a major role.


Jupiter is exalted in the 1st house of self, showing an identification with Jupiter. It rules the 9th house so it has a strong influence over matters of belief. Additionally, Jupiter’s twelfth-part is with that of Mercury in the 10th house of authority and actions, connecting it to the profession, teaching/lecturing, and recognition. Jupiter is very prominent. It is advancing in the fortunate 5th house and stationing direct within days of birth. Therefore, Jupiter pervasively characterizes life circumstances.

Jupiter overcomes Saturn and the 9th house by trine, and is itself overcome by the Sun which applies a trine from the first house within a degree. In this it has an ameliorating influence upon the adversity of Saturn and is fortunately influenced by the Sun, indicating recognition and leadership.


The negative indications associated with belief and foreign powers are apparent in the chart. They pertain to exile and issues with his homeland. However, the identification with the Moon and Jupiter put a strong focus on the 9th and 3rd houses as well as the pervasive role of Jupiter.

Dalai Lama with twelfth-parts
Dalai Lama XIV’s Tropical Natal Chart with twelfth-parts (outside wheel)

Sidereal – Mercurial Air Emphasis

The sidereal chart shifts the emphasis to Mercury, Mars, the Sun, and air signs. We lose the identification with Jupiter and the connection of Jupiter to the 9th. Jupiter is still prominent in the 5th house. However, Jupiter is no longer associated with the self (1st house) nor the 9th house. Jupiter’s twelfth-part is in the dark 12th house while Saturn is in the 9th house of God and rules there. The primary identification is with intellectual Mercury.

Dalai Lama FB Sidereal Natal

Dalai Lama XIV’s Sidereal Natal Chart with twelfth-parts (outside wheel)

Rational and Critical Outlook on Spirituality

All of this implies immense focus on rationality and a much more critical view of religion and spirituality. The Ascendant is an idea-oriented air sign, ruled by Mercury, occupied by Mercury and its twelfth-part. Rationality overload! The Sun and twelfth-part Mars are also both there showing a tendency toward a choleric belligerence. Venus rules the rising bound and is in the 3rd with the Moon but so is the twelfth-part of Saturn. Again, the stress is on doubt and materiality.

The sidereal chart fails to capture the fact that this person’s identity is tied up with religion and spirituality.

Ex. 6: Pope Francis I

The birth information for Pope Francis I is AA-rated for accuracy. The Pope’s chart is very similar to that of the Dalai Lama (above). Both have the Venus bound of Cancer rising, Saturn in the 9th ruled by Jupiter, and a prominent Jupiter (in VII).

Pope Francis I twelfth-parts
Pope Francis I’s Tropical Natal Chart with twelfth-parts (outside wheel)

Note on Southern Hemisphere

I’ve been told by a critic that the tropical zodiac does not work for the southern hemisphere. The logic is that some of the sign associations derive from the seasonal cycle of the northern mid-latitudes where Hellenistic astrology originated. Therefore, one might conclude that the sign meanings are dependent upon the seasons of a given place. By that logic, the tropical zodiac should be flipped when working in the southern hemisphere, at least in terms of things like domicile and exaltation relationships that reflect the seasons.

However, the seasonal associations are symbolic metaphors, not dependencies. Astrologers from Australia, South America, and the rest of the southern hemisphere regularly use the tropical zodiac with great results.

Note on Dignity

One reader, Theo, argued that Pope Francis’ chart convincingly shows that the tropical zodiac is inferior. He argued this because Jupiter is in Capricorn, its fall. By contrast, in the sidereal chart, it is in Sagittarius, its domicile, and with the Sun, which promises honors.

However, I have long argued that astrologers over rely on sign dignity. Sign dignity is a common factor rather than a particularizing one. Everyone born within about a one year period will have Jupiter in the same sign. It does not serve to define them as such. For instance, it doesn’t make everyone born with Jupiter in Capricorn a cynic. The problems with over-reliance on dignity do not magically go away by switching to the sidereal zodiac.

Sun-Jupiter Antiscia

Jupiter is actually very strongly connected to the Sun in the tropical chart. Jupiter and the Sun are antiscia each other within a degree, which has the force of a conjunction. Additionally, Jupiter rules the Sun. These indications connect Jupiter with the recognition and leadership significations of the Sun. Antiscia by degree is a symmetry relationship about defining points of the tropical zodiac (solstices for antiscia and equinoxes for contra-antiscia). As such it is not a relationship that is typically apparent to siderealists.

Pope Francis I Antiscia
Pope Francis I’s Tropical Natal Chart with Antiscia Positions (outside wheel)

Tropical – Mercury-Jupiter 9th and 7th House Emphasis for Actions

Let’s turn back to the tropical chart with twelfth-parts. We find Mercury, Mars, and Jupiter as pertinent to actions or occupation. Mercury is particularly relevant because it is strongly advancing (conjunct the Dsc), in phasis, and in an eligible place. Jupiter and Mercury are angular and together, as well as in each other’s bounds, connecting them strongly with the profession and with each other. This pertains to religious teaching, religious thought, and the like.

Mercury and Jupiter are both ruled by Saturn which is in the 9th house, Pisces, ruled by Jupiter. Therefore, there is a strong relationship indicated between the roles of Mercury, Jupiter, Saturn, and the 9th house in the profession.

Mars is in the 4th, an angle or stake, and is in sect. It rules the 10th and has its twelfth-part in the 11th house, closely with Mercury. I have noted that Mars is rather common as one professional indicator in charts of popes. Mars shows a competitiveness and its connection with Mercury connects it with thought, writing, and analysis.

Pope Francis I twelfth-parts
Pope Francis I’s Tropical Natal Chart with twelfth-parts (outside wheel)

Sidereal – Mercury-Jupiter 7th House Emphasis for Actions

For the tropical chart, I noted how there is a strong relationship between Jupiter in the 7th and Saturn in the 9th, as they rule each other. This linked the career to the 9th house of God more specifically. In the sidereal chart the link to the 9th house is tenuous.

Pope Francis I FB Sidereal
Pope Francis I’s Sidereal Natal Chart with twelfth-parts (outside wheel)

Mercury is far and away the most relevant planet of actions, with even stronger indications than in the tropical chart. Mercury is also very strongly linked with Jupiter and the Sun due to being with them and their twelfth-parts while ruled by Jupiter. However, the 9th house and Saturn are not strongly associated with those indications. Additionally, the twelfth-part of Mars is in the 9th house.

Hater of Religion?

As Saturn is in the 9th with the twelfth-part of Mars, and Saturn rules the 9th, there is little suggestion of anything other than dislike (negative associations) for spiritual aspects of the 9th house. The 9th is characterized by Saturn and Mars (oppression and aggression). By contrast, Jupiter’s benefits are focused especially on the 7th house (partners, sexuality), and also the 10th house (career), and 2nd house (money). Jupiter suggests marriage and career related benefits. The association with Mercury without a strong connection to a search for truth (9th) makes commerce particularly relevant.

The 9th House and Jupiter-Saturn

Does Saturn in the 9th reflect this Pope’s belief system? The strong interplay between Jupiter-Saturn, the 7th and the 9th, is not just appropriate to the Pope’s circumstances, it is spot-on. Not only do these things connect the 9th with the more spiritual indications of Jupiter, they also pertain to poverty, asceticism, and challenges that arise in relation to marriage and sexuality.

Pope of the Poor

This Pope has been active in fighting poverty and economic inequality as key issues to the point that many have accused him of being Marxist (see Marx’s own Saturn in Pisces in the 2nd above). He has stated that the Christian flag is that of the poor and that poverty is central to the gospel. Francis has embraced asceticism and like all popes has renounced marriage. Pope Francis is also sympathetic to atheists and those that believe in other faiths. He has stated that good deeds, particularly those that help the less fortunate, redeem one through Jesus, even if one is a nonbeliever or of another faith.

Challenges Pertaining to Sex and Marriage

Additionally, a Saturn ruled 7th in the 9th suggests religious difficulty (9th Saturn) associated with sexuality and marriage (7th). Sexual scandals involving pedophilia continue to plague the Catholic church under the Pope’s watch. Criticism of priestly vows of celibacy has also come to the fore. The Pope’s greatest challenges are likely to pertain to his handling of issues of sex and marriage. These associations are lost in the sidereal chart which does not strongly link Jupiter and Saturn together for 9th house matters.

Pope Francis I twelfth-parts
Pope Francis I’s Tropical Natal Chart with twelfth-parts (outside wheel)

Self-Identification, Water, the Moon, and Jupiter

The Pope also has some identification with Jupiter in the tropical chart as Jupiter is exalted at the Ascendant. By contrast, in the sidereal chart the main identification is with Mercury, planet of rationality. The Moon and water signs are also pivotal for temperament and character in the tropical chart. She rules the 1st house and has her twelfth-part there. The Moon is the Sect Light and is itself conjunct the twelfth-part of Jupiter, further linking it to Jupiter’s indications. The watery, lunar, jovial temperament is humane, sensitive, cheerful, and popular. By contrast, the sidereal temperament indications are for one who is airy and mercurial; a consummate aloof intellectual.

Pope Francis I FB Sidereal
Pope Francis I’s Sidereal Natal Chart with twelfth-parts (outside wheel)


With the chart of Pope Francis I, we see that even in the southern hemisphere the tropical zodiac is the most effective. The tropical zodiac not only shows us the role of a Mercury-Jupiter combination in the career, as the sidereal zodiac does, but it also connects that career with the self and the search for truth (9th house). Importantly, it also helps to describe the nature of belief in a more nuanced manner and its relation to other areas of life.

Ex. 7: Kurt Cobain

My final example is that of Kurt Cobain. His birth data is AA-rated for accuracy. I’ll be comparing career and character indications again. He has Virgo rising in the tropical zodiac, with 4 planets in Pisces in VII. In the sidereal zodiac he has Leo rising with only Mercury and the Sun in Aquarius in VII.

Character – Tropical: Earthy Temperament with Watery Mercury-Venus Complexity

In the tropical zodiac, Kurt’s Ascendant is in the Jupiter bound of Virgo, a relatively down-to-earth (earth sign) but playful (Mercury-Jupiter) position. Mercury, the Ascendant lord, is in Pisces, most closely with Venus, but also with Saturn and the Sun (and the Sun’s twelfth-part). This connects the identity as a mouthpiece (Mercury) but subjective and emotive (water) with the arts strongly tied to the identity (Venus co-present and the exalted ruler), and with close associations with hardship and depression (Saturn) as well as fame, recognition, and the “lyre” (the Sun).

Kurt Cobain twelfth parts
Kurt Cobain’s Tropical Natal Chart twelfth parts (outside wheel)

Character – Sidereal: Fiery-Airy Mercurial Temperament

In the sidereal zodiac, the Mars bound of Leo rises. Mars and the Sun bring a choleric or pushy temperament. However, the Sun is in Aquarius and with a very strong Mercury so the overall tendency is toward more intellectualism. There is no doubt that Kurt was very Mercurial, and this shows in both charts. Though the sidereal shows much more focus, direction, and clarity than the tropical, suggesting a more intellectual orientation. Fixed signs tend to linearly focused, and Aquarius, ruled by Saturn, is rather detached, while Leo is showy.

Kurt Cobain FB sidereal
Kurt Cobain’s Sidereal Natal Chart with rwelfth-parts (outside wheel)

Venus is no longer tied strongly to the identity, nor is water. So we don’t get the same sense of confusion and synthesis (mutability), the arts (Venus), and the personal or emotional (water).

Profession – Tropical: Mercury with Venus-Saturn-Sun

In the tropical chart, Mercury is the most relevant of the planets of actions. It is in the eligible 7th place, it rules the 1st and 10th, and it is conjunct the Descendant (strongly advancing). Mercury is also with the Sun and receiving the application of the Moon. However, Venus is with Mercury and she also very relevant for actions as she strongly advances in the eligible 7th and has her twelfth-part in the 5th. Mars and its twelfth-part are in the 3rd so they are not so relevant.

Kurt Cobain twelfth parts
Kurt Cobain’s Tropical Natal Chart twelfth parts (outside wheel)

The Mercury-Venus combination was discussed already with Jimi Hendrix (above). It combines vocals and composition (Mercury) with art (Venus). With the Sun present it can pertain also to guitar and to recognition or fame. In the tropical zodiac we see a close link with Venus (arts, love) and Saturn (struggle, depression). These themes and the Piscean mutability, water, and link with fame (ruled by Jupiter in XI, Sun present) all strongly express career circumstances.

Profession – Sidereal: Mercury with Sun

Mercury is the planet of actions in the sidereal chart as well. Venus still has relevance to actions as she is in the 8th and she rules the 10th. The strong link between Mercury and Venus is lacking though so their significations don’t readily combine. The solar link with Mercury is more pronounced as the Sun rules the Ascendant signifying identification with the heroic Sun. Mercury with the Sun represents a strong skill linked with that solar mission. A visionary solar-Mercurial quality to the profession is possible, though things appear more intellectual or political (Mercury-Sun, airy and fiery) than pertaining to emotional expressive arts.

Kurt Cobain FB sidereal
Kurt Cobain’s Sidereal Natal Chart with rwelfth-parts (outside wheel)

The tropical chart reveals more of the emotional and artistic quality as well as many of the contradictions. From the vacillating mutability to the contrast between a self-deprecating earth-water temperament and an immense drive for fame (Sun with personal and career factors). Saturn (hardship, depression) is connected to Venus in both charts but Saturn’s connection to the personality and main planet of actions (Mercury) is more direct in the tropical chart.

Part II: Logic

The Geocentric Logic of the Tropical Zodiac

Upon meditating on this matter for some time, I’ve come to understand the greater logic of the tropical zodiac. Astrological symbolism is geocentric. The indications of the chart are always relative to a specific time and place on Earth.

The ecliptic is the road or path of the wandering stars. A twelve sign zodiac is a regular meaningful way of dividing this road symbolically in accordance with numerical symbolism and the twelve month calendar. We can slice such that a certain star or stars coincide with a key spot in this division and that will produce the sidereal zodiac. However, a more geocentric strategy is to divide the road of the planets according to its intersection with the road of the Earth, the equator.

Equator as the Road of the Earth

From a common perspective we think of the Earth as a top, spinning with the south side down. However, there is no intrinsic up or down. The assigning of up to north is relatively arbitrary. The Earth is just as much rolling like a ball as spinning like a top, depending on perspective.

It is rolls on a path marked out by the plane of the celestial equator. The equator is the path or road of the Earth, much like the ecliptic is that of the wandering stars. The intersection of these roads marks the equinoctial points. Their maximum divergence marks the solstitial points. If we are to divide the space-time of the planetary road, then from a geocentric perspective there is no more perfect set of reference points than its intersection with the the equatorial road of the Earth.

Intersection of the Equator and Ecliptic (public domain)

The Sidereal Zodiac Disregards the Earth-Ecliptic Relationship

By contrast, the sidereal zodiac much more arbitrarily divides the road of the planets into regular sections to overlay irregular groupings of stars. The division is divorced from the path of the Earth (equator). Understandably, there is controversy regarding where the slices should be made in the sidereal zodiac as different stars can be used as the key reference star. Additionally, the sidereal zodiac is superfluous when it comes to studying the direct interaction of planets with stars and constellations. We can study the motion of the planets against the stars independently from the zodiac.

Origins and Feature-Bundles

The zodiacal signs are associated with the characteristics of the constellations and seasonal periods which coincided with them around the time and locale of its birth. In my article on the signs, I’ve referred to these characteristics as the “feature bundles” of the signs. I’ve also pointed out that the more critical of those features are derived from the seasonal or tropical cycle than the constellations themselves.

However, the zodiac doesn’t depend on the constellations or seasons for its meaning. It derived associations from constellations and seasons from the time and place of the assigning of those associations. The origin of the zodiac’s associations lies in the northern hemisphere at a time when both tropical and sidereal zodiacs roughly coincided. These original symbolic roots are still embedded in its meanings. This parallels how our own origins (birth chart) are embedded in the associations which pertain to the circumstances of our lives.

Part III: History

Hellenistic astrology arose at a time when both zodiacs nearly approximated each other. The zodiacs coincided exactly in the early 3rd century CE (about 220 CE per the Fagan-Bradley ayanamsha). The bulk of Hellenistic material on the qualities of the signs is from the first few centuries CE. There is evidence that in some locales a shift to a tropical standard was already underway by the 5th century BCE. Additionally, Geminos advocated for the tropical zodiac in the 1st century BCE for reasons independent of precession. He made no mention of precession in his arguments.

Despite awareness of the sidereal zodiac and the shifting of the constellations, Ptolemy advocated for a switch to a tropical standard in the 2nd century CE. This was very early on in the western tradition. His arguments were successful. The tropical zodiac became the de facto standard for most traditional western astrology thereafter.

Babylonian Zodiac Origins

The twelve sign zodiac is a Babylonian innovation, though much of its associative meanings (feature-bundles) came about during the Hellenistic period. In approximately the 5th century BCE we see our first evidence of a standard zodiac with twelve signs of 30 degrees.

The Babylonian regular zodiac was undoubtedly intended to be sidereal. Two competing Babylonian standards for fixing the zodiac arose around that time. From System A, one standard put the vernal equinox at 10° Aries. From System B, the other standard put the vernal equinox at 8° Aries. These standards arose at about the same time (System B shortly after System A) and were both used throughout the whole of the use of the regular zodiac in Babylonian astrology. However, the Babylonian zodiac was sidereally fixed such that updated tables of computed planetary positions tended to account for precession, despite lack of knowledge of precession.

Development of the Babylonian Zodiac

The development of the zodiac was preceded by the long-standing use of zodiacal constellations and their boundaries. This was the original zodiac of the constellations. There was also a long-standing use of stars in the belt of the ecliptic as points of reference (Normal Stars).

However, the the Babylonian constellations of the ecliptic numbered 18 (occasionally two are combined to make 17) and were irregular in size. The regularizing of the zodiac into 12 equal segmets was preceded by the development of an “ideal” 12 month calendar of 30 days per month. This calendar was correlated with the twelve sets of (the more than twelve) constellations which the Sun traveled through during various months. As the vernal equinox was significant for the beginning of the Babylonian year, the first month was assigned to when the Sun was in the constellation now known as Aries (then known as the hired man).

Therefore, there was from the beginning a consideration for correlating the ideal seasonal calendar with twelve groupings of constellations. Also, note that the zodiacal constellations of the Babylonians included many familiar ones but also some that were different. The Greek astronomers, particularly Eudoxus in the 4th century BCE, gave them their familiar twelve forms.

Calendar to Zodiac

One can posit the following steps in the development of the zodiac, although it must be said that our knowledge of how the zodiac was first devised is provisional. The division of the schematic calendar into 12 months of 30 days each […] could be correlated with twelve constellations through which the sun was found to travel in a one ideal “year” of twelve 30-day months. Because the spring equinox, which was always close to the beginning of the Babylonian year, was to occur in Nisannu (I.15 according to the tradition of MUL.APIN), then Nisannu, or month I, was when the sun was in the constellation Aries […] (Rochberg, 2004, p. 129)

Note the much older association between the spring equinox and the 15th day of the first month. This association predates the actual creation of the regular 12 sign zodiac. However, this association may be the source for the Alexandrian scheme that I mentioned in my article on sign symmetry. This is an older Babylonian association of the equinox with the mid-point of the first month, at a time when the Sun would be in the constellation Aries.

Importance of the Equinox

As noted, even before the advent of the regular zodiac, the equinox was significant in the Babylonian calendar (marking the 15th day of the 1st month). The position of the equinoxes and solstices continued to be a matter of central importance in late Babylonian horoscopy as well.

Solar phenomena incorporated within horoscopes are the longitude of the sun at the time of birth, the date of either solstice or equinox within a month or two of the birth date, and the occurrence of a solar eclipse within the year of birth. (Rochberg, 2004, p. 133)

Earliest Appearance of the Zodiac

The earliest direct evidence for the existence of the zodiac comes from fifth-century astronomical texts […] in which positions of the planets are cited with terminology used with respect to zodiacal signs as opposed to zodiacal constellations. (Rochberg, 2004, p. 130)

Rochberg noted that there is also some indirect evidence of the use of zodiacal signs in the early 5th century BCE.

The phenomena computed in these texts can be dated with relative certainty to 475 B.C., although the writing of the tablets was certainly much later. (Rochberg, 2004, p. 130)

Names Not Constellations

The segments of longitude were given the names of the constellations but the real purpose of this sidereal zodiac was to compute exact positions. The signs were not simply the constellations. Constellations greatly vary in terms of size on the ecliptic with some encroaching on signs named for different constellations.

Although the names of the zodiacal signs derived from an original relation to the zodiacal constellations, once the signs were defined by longitude rather than the constellation they ceased to have any real relation to the constellations and became a mathematical reference system, representing the 360 of the ecliptic, counted from some defined starting point. (Rochberg, 2004, p. 128)

Lack of Recognition of Precession

Furthermore, there were two standards for the whole of Babylonian use of the zodiac over multiple centuries; the 8 and 10 degree Aries standards. This shows that the Babylonians didn’t recognize precession.

In mathematical astronomical texts, the equinoxes and solstices were also normed sidereally at 10 Aries in System A and 8 Aries in System B. That the cardinal points of the year do not correspond to the zero points of the appropriate signs in the Babylonian zodiac is a result of the sidereal (rather than the tropical) construction of the zodiac. The two systems of Babylonian mathematical astronomy maintained the two norming points throughout the period of their use. As Neugebauer pointed out, neither the chronological relation between Systems A and B norms nor the reason for their difference is understood. That both vernal-point longitudes remained sidereally fixed, however, proves precession was not recognized. (Rochberg, 2004, p. 132)

Where to Start

Many have sought to identify the key original reference stars for the Babylonian zodiac. However, most attempts to do so are based on evidence that precedes the actual creation of the twelve sign regular zodiac. There were certainly reference stars used in other contexts for observational data that preceded the signs by many centuries. Computing relationships between those reference stars and other observed phenomena such as an equinox, one can construct a pseudo twelve sign zodiac as it might have hypothetically appeared if the zodiac had existed then.

Indirect evidence has also been used, but not often very credibly. For instance, correspondences between calendrics and the stars can be used, or calendrics and the equinox. For instance, the equinox on the 15th day of the first month in a given age may be taken as similar to putting the equinox at the mid-point of the first sign in that age. However, such inferences can be only hypothetical when there is no evidence for the use of regular sign-based zodiac in that age.

No Clear Ayanamsha

Unfortunately, when it comes to the regular twelve sign zodiac and the two Babylonian standards, scholars have been clear that no norming star has yet been found. Claims have been made but refuted by leading scholars.

More precisely, however, we still cannot establish the star that originally served as norming point for the ecliptic. Even were we to assume the vernal point was determined correctly when it was assigned to 10° then 8° Aries, the corresponding dates of these zodiacal norming points cannot be pinpointed, as we do not sufficiently understand the ancient methods to obtain those values. Comparison against modern values for the longitudes of equinoxes is therefore uninformative for this purpose. (Rochberg, 2004, p. 133)

Hellenistic Use of System B

System B was influential upon early Hellenistic astrologers. Some early Hellenistic astrologers, like Thrasyllus (late 1st century BCE to early 1st century CE) used Babylonian System B. These astrologers explicitly advocated for placing the equinox at 8° Aries. For instance, see the doctrines attributed to Thrasyllus in Vol. X of the Hellenistic Track by Project Hindsight p. 57-58. It is said that Thrasyllus advocated placing the equinox at 8° Aries rather than 0° Aries. This suggests there were astrologers in his time that used the tropical zodiac.

Furthermore, it is unclear whether some of the astrologers like Thrasyllus who set the equinox at 8° Aries were truly using a sidereal or tropical reference point. The Babylonian norming point is lost to history, and the strong reference to the equinox at 8° Aries suggests that the equinox was taken up as a norming point by some astrologers (a type of tropical zodiac). Updated Babylonian tables might have reflected positions with greater sidereal accuracy if available to the astrologer. However, computations from the equinox common among Greek astronomers, would result in a tropical zodiac, defined with respect to the equinox, albeit with the equinox set at 8° Aries.

The tropical zodiac was within only a few degrees of the sidereal zodiac during this time period. By contrast, an offset tropical zodiac in which the System B value for the equinox (8 Aries) was used to compute positions would be 5-8 degrees from the sidereal zodiac of the 5th century BCE Babylonians, as well as most major sidereal zodiacs advocated today (including Fagan-Bradley).


It is well known that Vettius Valens was one of the Hellenistic astrologers who adopted an 8° Aries vernal equinox from System B (and rising times from System A). However, Valens appears to have had access to updated Babylonian tables as his values are typically only a few degrees error (few degrees greater) than modern computed tropical values. Valens operated in the late 2nd century CE when the tropical and sidereal zodiacs almost exactly coincided. At that time a siderealist would’ve been better off starting the zodiac with the vernal equinox, as the two matched up within a degree in his time. However, astrologers were not aware of precession and simply used whatever tables were available for finding planetary positions, while assuming the equinox was at 8° Aries. By consequence, many of his positions are in the wrong sign by today’s tropical and sidereal standards.


A sidereal zodiac must be referenced by a star rather than the equinox, or it will accumulate error due to precession. Hipparchus is known to have discovered precession in the 2nd century BCE, after the advent of the zodiac. Hipparchus estimated precession to be at least 1 degree every 100 years (now known to be a degree very 72 years). Therefore, if System B put the vernal equinox at sidereal 8° Aries in say 432 BCE, it would correspond to 2 Aries in 0 CE. This is because 360 years is equivalent to 72 times 6, representing a 6 degree shift relative to the equinox. Therefore, Hellenistic astrologers of the 1st through 4th centuries using a standard from System B but withthe equinox as norming point would be using a zodiac with a huge error of 5-10 degrees.

A Matter of Convenience

The finding that some Hellenistic astrologers thought they were using a sidereal zodiac does not strongly support the position that we should use a sidereal zodiac for Hellenistic astrology. Those astrologers likely thought they were using a zodiac that was both sidereal and tropical. They used an outdated Babylonian standard without knowledge of precession. Some astrologers with access to them used updated Babylonian tables which would over time account for some of the effect of precession.

It is also likely that some astrologers simply used the equinox at 8° Aries as a norming point resulting in a type of tropical zodiac, though one offset 8 degrees from the familiar one. That appears to be the implication in the Thrasyllus fragments and the account of Geminos (see below). In conclusion, for Hellenistic astrologers unaware of precession the zodiac was fixed both tropically and sidereally. The matter of computing zodiacal position was one of convenience owing to the mathematical sophistication involved and the availability of tables.

Tropical Zodiac Origins

It is often believed that Ptolemy came up with the tropical zodiac in the 2nd century CE. The tropical zodiac has actually been around since the 5th century BCE. Furthermore, Geminos of the 1st century BCE, whose work contained some limited astrological doctrines, explicitly and vehemently advocated for the use of a tropical zodiac and against the 8° Aries standard in no uncertain terms.


The two solstices and the two equinoxes occur, in the way of thinking of the Greek astronomers, in the first degrees of these signs; but in the way of thinking of the Chaldeans, they occur in the eighth degrees of these signs. The days on which the two solstices and the two equinoxes occur are the same days in all places, because the equinox occurs in all places at one time, and similarly the solstice. An again, the points on the circle of the signs at which the two solstices and the two equinoxes occur are exactly the same points for all astronomers. There is no difference between the Greeks and the Chaldeans except in the division of the signs, since the first points of the signs are not subject to the same convention for them; among the Chaldeans, they precede by 8 degrees. Thus, the summer solstitial point, according to the practice of the Greeks, is in the first part of Cancer; but according to the practice of the Chaldeans, in the eighth degree. the case goes similarly for the remaining points. (Geminos, Ch. I, #9, Evans & Berggren trans., 2006, p. 115)

Almost as Old as the Sidereal Zodiac

It has been attested that the Babylonian regular zodiac of twelve signs entered into Greece very soon after it appeared in Babylon in the 5th century BCE. There is in fact evidence for the use of the tropical zodiac among the Greeks as early as the late 5th century according to renowned historian of science, Otto Neugebauer. Please note that the early 5th century provides the first evidence for the Babylonian regular sidereal zodiac, less than a century earlier.

We know from Hipparchus that the majority of the “old” mathematicians divided the ecliptic in this form. This statement agrees with sources still available to us; Euctemon (about -430) placed all four cardinal points on the “first day” of the respective signs. The same norm holds for Callippus (about -330) and is underlying the era of Dionysius (beginning -284/3). As far as we know this norm is attested nowhere in Babylonian astronomy. (Neugebauer, 2012, p. 600)


The tropical zodiac became the de facto standard for western traditional astrology as a result of Ptolemy’s Almagest (2nd century CE). Ptolemy’s work was the state-of-the-art for astronomy of the day, and he was also an astrologer. Building upon Babylonian records, work done by Hipparchus (2nd century BCE) on precession, and a thorough understanding of the relevant math, Ptolemy constructed the most advance geocentric model of the heavens of the ancient world. Most later Hellenistic astrologers familiar with his work were confronted by the realities of precession and found his arguments for the adoption of the tropical zodiac to be compelling. However, in the Perso-Arabic period, noted for both Hellenistic, Indian, and Persian influences, there continued to be some back-and-forth between astrologers using tropical and sidereal calculations.

Further Reading

For further reading on the historical matters of the zodiac in early Hellenistic astrology, please see Rob Hand’s excellent article, “On the Invariance of the Tropical Zodiac“. I also recommend Francesca Rochberg’s book, The Heavenly Writing. for details regarding Mesopotamian astrology. For a really deep dive into the history of astrology and astronomy, see the History of Ancient Mathematical Astronomy by Otto Neugebauer. Also see the Almagest by Ptolemy for a look at his arguments regarding precession and the tropical zodiac.

Part IV: Epilogue

Skepticism and Experimentation

Arguably, if it weren’t for the tropical zodiac, I would’ve never studied astrology. I’m a skeptical individual. When I was about 15 years old, I had a running joke of asking new people I’d meet their Sun sign. It was a joke because I didn’t believe in astrology at all. I thought people who believed in astrology were ridiculously naive. However, I was a bit of an oddball with a dark sense of humor. Somehow I found it perversely amusing to collect this strange information from people and observe their reactions to the question.

Women Under Watery Suns

Fast forward one year and things started to get weird, particularly as concerns women who had their Sun in a water sign. Maybe it has to do with my own Moon-Venus conjunction in water, but I started to notice a common “vibe” among women with a water sign Sun. I could also often pick up on the subtle ways the water signs differed. When I correctly guessed the Sun signs of two Scorpios and one Cancer on first encounter with them the damage was done. I knew there was something there that I was picking up on and that there was some validity to astrology. My world has not been the same since.

Astro-Junky #7

Being a thinking person, I constructed my own elaborate theories on the meanings of Sun signs and how astrology worked. I also read everything I could on it. Books on Sun-Moon combinations were consumed, then ones on the rising sign, then those on the whole chart. I even took a cassette audio course on natal astrology. With every volume of Noel Tyl’s “The Principles and Practice of Astrology”, I made flash cards for every configuration.

Unfortunately, like many who come to modern astrology, I began uncritically adopting all of the common metaphysical assumptions. The chart was a map of the soul. Transits and progressions represented actual movements and events in the soul, whether or not we were aware of them or they actually manifested. Jungian psychology provided the key to understanding the chart. Meditation, psychedelics, and the law of attraction provided the keys to cleaning up the opaque psychic machinery so it could become a sparkling jewel of bliss.

Energies vs. Personalities

So, what’s the point of this long discussion of my juvenile obsession with psychological astrology? Yes, I was naive, and my path was cliched, but that’s not the point. The point is that I’m not alone. Many come to astrology due to some subtle direct encounter with the “vibe” or “energy” of the tropical signs of the zodiac. Those who pay attention can pick up on these “vibes” particularly as they concern the tropical sign rising and that of the sect light (Sun by day; Moon by night). Intuitive encounters with the “energies” of these signs has helped immensely with the popularity of modern western astrology. This is especially so when it comes to the popularity of Sun, Moon, and Ascendant sign astrology.

Where Modern Astrology Gets It Wrong

Hold up. I’m not saying that modern western astrology has things right. I strongly believe that the chart is not a map of the psyche with planets as its functions. In hindsight, all these water sign women had day charts with a water sign Sun as Sect Light. They also had very different personalities even when they shared the same Sun sign and its vibe. Things like introversion vs. extroversion, level of aggression, intellectualism, professional inclinations, preferences, and moral compasses were often vastly different. An amorphous “vibe” and a core personality are not the same thing.

Narrative Elements vs. Mapped Landmarks

I actually believe it is reckless to confuse the Sun in a chart for the ego, or even a personality “center”. This is not to say that the Sun doesn’t pertain to egotism nor that the Sun can’t be a powerful factor for symbolizing a person’s personality. It can symbolize such things in a systematic manner and ancient astrology tells us when and how. However, a “vibe” that is occasionally apparent with some people does not entail a thing that is always there but deeply repressed when that “vibe” is not apparent. I could go on but this is a topic for another time and another article.


The primary reason to use the tropical zodiac is that it produces better results. When applying Hellenistic and early medieval techniques, we get more information out of the tropical signs and their divisions, including the bounds and twelfth-parts. This holds whether we are finding significators of special topics, such as character or profession, as well as when looking at associated themes. Furthermore, its is effective in the southern hemisphere, so indications are not dependent on the specific nature of the seasons as some have claimed.

The tropical zodiac is also the more logical choice for dividing up the space-time of planetary travel. It captures the geocentric nature of astrology and the central importance of the equinoxes and solstices. History also supports the use of the tropical zodiac. The tropical zodiac no longer corresponds to the constellations but it did in the Hellenistic period when its key associations came about. It derived those associations from the stellar and seasonal characteristics of that time and place. The persistent symbolism of a foundational time and place is something with which all astrologers should be able to relate.


Geminos (2006). Introduction to the Phenomena. (J. Evans & J. L. Berggren, Trans.). Princeton, NJ. Princeton University Press.

Neugebauer, O. (2012). A History of Ancient Mathematical Astronomy. Springer Berlin Heidelberg. Retrieved from https://books.google.com/books?id=6tkqBAAAQBAJ

Rochberg, F. (2004). The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture. Cambridge University Press. Retrieved from https://books.google.com/books?id=TjiVXdSMRu4C

Featured Image (cropped) is in the public domain. It is from Andreas Cellarius Harmonia Macrocosmica, 1660/61. Chart showing signs of the zodiac and the solar system with world at centre.

Update 01/12/2019

This article was updated as the prior sections on Valens concerning the degree of error in his calculations were incorrect. I discovered this upon reading Greek Horoscopes by Neugebuaer and Van Hoesen (p. 171-172) where they discuss how the shifting error in his work is typically of 2-3 degrees and is consistent with calculations that are sidereally-based.



Student of astrology since the mid-nineties. Business owner, husband, and father of three. I enjoy hiking, reading, making music, and learning languages.

8 thoughts on “Why Use the Tropical Zodiac?

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  • January 21, 2019 at 5:39 pm

    Excellent article! I do have a question though. I recall you mentioning in a different post that you recommend precession-corrected solar returns. I agree that they seem to work better than solar returns that are not precession-corrected, but I’m wondering what explanation can be given for using a sidereal reference point for solar returns. Any thoughts about that?

    • January 21, 2019 at 6:27 pm

      I do love precessed resturns. I use both precessed and zodiacal (non-precessed) returns but I have often found that the precessed make more sense in terms of the later medieval approach to returns where the Ascendant of the return is very important.

      Sidereal cycles are important, as are the stars themselves, and the constellations. A sidereal return is the return of a body to its same position relative to the stars. When I do sidereal returns I use the tropical zodiac. These are two different matters. From a geocentric perspective, there is our fixed reference of the celestial equator (path of the earth) and the regular division of the ecliptic gets defined relative to that more fixed sphere (from the geocentric perspective). The sphere of the “fixed stars” moves forward against that at the rate of about one degree every 72 years. It is a very slow movement but it is in the same direction as the spheres of the planets. Just as synodic cycles, such as the Jupiter-Saturn conjunctions, are very significant, so are the sidereal periods of the planets. The precessed return is simply a return to the Sun’s position relative to the stars, and in my opinion is not dependent on the zodiac at all. Sidereal periods of the planets were used by the Babylonians prior to the advent of a regular zodiac. The solar returns of the early Hellenistic astrologers (and many of the later Perso-Arabic ones) were based on sidereal periods as well because the tables they used were computed based on sidereal and synodic periods.

      The impetus for having a 12-sign rather than 17 or 18 sign zodiac is significant. The Babylonians thought their zodiac was both tropical and sidereal, as scholars have pointed out there is no evidence for knowledge of precession. The Babylonians used 18 constellations prior to, and even in the early period of, the regular 12 sign zodiac. The 12 signs were named after members of the original 18 constellations in the path of the Moon, but there was no long-running prior use of a (only) twelve constellation zodiac, in which twelve constellations spanned the length of the ecliptic. It is pretty well documented that it was the ideal 12 month (12 Moon) calendar with 30 day months which prompted the desire to have a zodiac that was regular containing 12 signs each of 30 degrees. I’ve heard the tropical zodiac called “just a glorified calendar” by critics, but actually there would be no 12 sign 30 degree zodiac at all if it weren’t for the influence of the annual calendar. The zodiac that wasn’t so tied to the 12 month calendar was the 18 constellations in the path of the Moon.

      The Babylonians had synodic and sidereal periods for the planets which they used to generate their ephemerides, so in practice their zodiac was sidereal, complicating matters. But some key facts are often left out of the zodiac debate: 1. that precession was not known to the Babylonians; 2. the calendar (not constellations) were the basis for division into 12 signs of 30 degrees as the Babylonians used 18 constellations, not 12 in their earlier astrological work; 3. an explicitly tropical zodiacs were used by many Greek astronomers pretty much as soon as the zodiac entered Greece (less than 100 years after its created by the Babylonians); 4. the character of what came to be the 12 constellation zodiac is essentially from Greek astronomers of the 4th century BCE, despite the fact that many of the constellations were borrowed from the Babylonians – many constellations were combined, altered, renamed, and just generally changed, which is why we have no “hired man” but do have Aries, no “great one” but do have Aquarius, and Pleiades and Bull are one in Taurus, Swallows and Fish Tails are one in Pisces and so on; 5. essentially tropical characteristics were assigned to the regular signs in Hellenistic astrology which continue to be the most drawn-upon sign features in astrology (east and west).

      I’m getting very long-winded but my point is that the stars and sidereal periods (including of one’s natal Sun) are very important astrologically but I feel that when it comes to dividing the zodiac it makes the most sense to do so tropically. Also, when it comes to both matters, comparing results is extremely important.

      Best wishes,


      • January 22, 2019 at 7:55 pm

        Thanks for the detailed answer to my question. I’ve been thinking along the same lines as what you said, that the tropical zodiac is separate from measuring periods of time in a sidereal fashion.

        Keep up the good work! Your posts are great and the clearest explanation of hellenistic astrology I’ve seen online.


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  • December 21, 2018 at 5:12 pm

    Wonderful as usual, Anthony! Many thanks.

    Recently I’ve read trad astrologer Patrick Watson suggesting a reason for the astrological pertinency of north hemisphere’s seasonal symbolism: Earth travels northward in the galaxy. So we could think of the northern hemisphere as a “front seat” of our vehicle.


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