The Two-Zodiac Problem

Toward an Empathic Understanding

By Glenn Perry

And God said, “Let there be lights in the expanse of the sky to separate the day from the night, and let them serve as signs to mark seasons and days and years…” And it was so.
~Genesis I:14-15


Author’s Note: The following is a verbatim transcript of a talk I gave at the IVC India Conference in Kolkata, India, on February 2,  2018. The lecture was a summation of ideas developed more fully in an article published in Constellation News, edited by Sri Gopal Bhattacharjee. For discussion of the controversy surrounding the lecture, click: Are We Free to Discuss Astrology’s Real Problems?

As you can see, I’ve chosen to start my talk with a cartoon depicting an elephant seeking therapy for his plight of not being acknowledged. The elephant in the room generally symbolizes a difficult topic we try to avoid, perhaps out of politeness, or simply because it’s a problem for which we have no solution. Clearly, the elephant in the room at this historic conference where east meets west is that anxiety ridden question: can two zodiacs co-exist without contradiction―or, is one zodiac correct and the other wrong?

As we all know, astrology originated with the zodiac, which like a cosmic womb is the source for everything that follows. But, we also know that our field is currently divided by two different zodiacs, tropical and sidereal, each of which claim parentage of the same child―astrology itself.

The situation is not unlike the story from the Hebrew Bible in which two women living in the same house both claim to be mother of a child. It fell upon King Solomon to make a judgment as to who was the true mother.

Our Solomonic problem, if I can call it that, derives from contradictory ways of defining the zodiac. The tropical zodiac is defined by the seasons and is disconnected from the stars as a frame of reference, whereas the sidereal zodiac is defined by the stars and is disconnected from the seasons as a frame of reference.


Zodiac with Constellations

Zodiac is a 16° Band Around the Sun


Both zodiacs use a 30-degree, 12-sign system in which the meanings given to signs are roughly similar yet fall on different dates. And both zodiacs reside along the ecliptic, which is the Sun’s equator extended into space. Because the planets orbit the Sun within eight degrees above or below the plane of the ecliptic, the zodiac is a 16° band circling the Sun. However, this is where the two zodiacs part company.

The sidereal zodiac is comprised of 12 equal, 30-degree constellations―groupings of stars―visible along the ecliptic. And while both zodiacs begin with Aries, the sidereal zodiac defines Aries in terms of fixed stars.

Vernal Point = Intersection of Celestial Equator and Ecliptic


Conversely, the tropical zodiac places Aries at the vernal equinox (first day of spring), which is where the earth’s celestial equator intersects the plane of the ecliptic due to the earth’s axis being tilted at an angle of 23° relative to its orbital plane.

Before exploring how the two-zodiac problem might be solved, let me dispense with one approach that’s unlikely to be helpful: The claim that both zodiacs are equally valid for their system. 

As whole systems, differences between western and Vedic astrology are relatively superficial, with more overlap than difference. Conversely, the difference between the two zodiacs is fundamental and irreconcilable. It will do us no good to hedge the issue.

Aristotle’s law of non-contradiction states that contradictory statements cannot both be true in the same sense at the same time. Put simply, a thing cannot be itself and not itself; March cannot be March and February. Two zodiacs that assign the same meanings to different dates and different meanings to the same dates are inherently contradictory.

Mutual tolerance for both zodiacs may be a feel-good, politically correct position, but it is also an intellectually lazy one.

I also don’t think personal, subjective experience can tell us which zodiac is correct because there are too many ways an astrological archetype can be represented in a chart.

In the end, all that matters is whether an explanation is persuasive; that is, whether it explains the facts of the matter in a clear, comprehensive and convincing fashion.

Most treatments of the debate focus on whether the ancients measured planetary position from the fixed stars, or from the equinoctial and solsticial points. A star-based measurement system would favor the sidereal zodiac; measuring from the cardinal points would favor the tropical. In fact, as we shall see, the original zodiac was actually a hybrid defined by fixed stars and cardinal points.

But really, this misses the point. The important question is why the zodiac came into being in the first place. For what purpose did it originate?

The entire two-zodiac controversy hinges on a single question: Could constellational meanings have originated independent of seasonal processes? That is, could the constellations have come into being without being anchored to the equinoctial and solstitial points?

In astrology, the mutable signs are associated with intellectual inquiry. Gemini facts lead the way, followed by Virgonian analysis. Sagittarian abstract reasoning looks at the evidence to see if it supports or refutes a hypothesis. Then, there’s Pisces, which is the least intellectual of the mutable signs, but perhaps the most critical to our task.

Pisces is direct perception, or knowing by empathic connection with the thing known.

Unless we can place ourselves in the mind-set of early humans when the night sky first took on meaning, our treatment of the problem is apt to be short-sighted, a dry, objective analysis and interpretation of facts, but without any depth of understanding. To achieve depth, we must utilize the gifts of Pisces: imagination, and empathy.

We must imagine what it was like before astrology, and try to empathize with early humans gazing upwards as the stars slowly drifted across the vault of heaven…seeing the Moon grow larger night to night, finally full, then smaller, and eventually returning to full again, each month in a different sector of the night sky.

And with each lunar cycle there were corresponding changes on earth―alterations in duration of light and darkness, heat and cold, vegetative cycles and animal migrations―always following the same sequence, year after year, until gradually the sequence became predictable.


Early Human Stargazers


For early humans, life was harsh, brutal, and short. One could die in a dozen ways, none of them natural―starvation, bear attack, or simply the bitter cold. Adapting to the rhythms and cycles of nature was critical to survival. Observation of the night sky focused on one all-important question: as the stars move, what happens here, in my world? What happens to me?

Of special significance were the stars that rose just ahead of the Sun at dawn (heliacal rising). For every lunar cycle, the Sun inhabited a sector of sky that became associated with earthly phenomena that occurred during that 30-day period. Such sectors came to be known as constellations that heralded specific times of year.

As days grew longer or shorter, nature reflected changes in the duration of daylight in an ever-repeating yearly cycle. The rains came, rivers flooded, bears awoke from hibernation, flowers bloomed, trees lost their leaves, animals migrated, lakes froze, round and round, always the same sequence on earth, always the same constellations above.

Sky God

Superhuman Sky Gods


Understandably, the ancients concluded it was the constellation the Sun was currently occupying that determined such changes. In Babylonia, where the zodiac originated, it was assumed that the constellations were formed at the beginning of time by all-powerful sky-beings. The figures that populated the heavens were not simply passive symbols representing the seasons; they were superhuman, celestial gods with a direct, causative effect upon the world of humans.

Every constellation, every month, had its own meaning and signaled to the tribe the requisite activity to be performed― migrating salmon headed upstream, spear them; strawberries ripe, pick them; chestnuts fallen on ground, store them. The starry heavens comprised the ancient calendar and were a means for organizing time into discernible segments and qualities; but they were also messengers whose annual appearance told humans what to do now.

Early AgricultureBy the time agriculture began in approximately 10,000 BC, observation of the night sky turned serious. There was an exact right time for planting crops and you could easily get it wrong if there was an unseasonably warm period in mid-February. The ability to predict when the seasons were about to shift was critical to the survival of the tribe and was the prime motivation for observing the changing sky. Knowing the proper times for sowing, cultivating, and harvesting crops were universal human concerns and the basis for organization of communal life.

Toward this end, the Sun’s latitudinal movement along the horizon at dawn was of particular importance. For six months, the Sun rose in a progressively northern latitude as days grew longer, then turned (tropos) at the constellation Cancer and moved in a southern direction as days grew shorter.

Upon reaching sidereal Capricorn at its most southern latitude, it turned again. During its northward movement, it arched higher across the day sky; during its southern trek, it hung lower.

The annual back and forth movement of the Sun along the horizon had four discernable stages ― two equinoxes and two solstices ― marking seasonal changes in accordance with durations of daylight and night. At the vernal equinox, days and nights became equal but daylight was increasing; at the summer solstice, daylight was maximum but subsequently days got shorter; at the autumnal equinox, days and nights were again equal but darkness was increasing; and at the winter solstice, daylight was minimal, but again began to increase. These dates and their corresponding constellations marked the turn of the seasons.

Activities performed at various times of the year ―plowing, planting, harvesting ― became associated with the constellational deity that ruled that phase of the year. Monthly rituals, festivals, and appropriate sacrifices all occurred in synchrony with the annual appearance of the representative constellation at dawn. Myths evolved to explain how and why the gods controlled their corresponding seasonal processes. In this way, natural events were symbolically encoded in allegorical representations. This made the constellations memorable, which was critically important at a time in history when writing did not yet exist.

Because each month had its own quality, zodiacal constellations were metaphors of seasonal processes occurring in nature. Aries is spring-like as nature is heating up and new life is sprouting, bold and fresh. Libra is balanced, just as the duration of light and darkness is perfectly balanced at the start of autumn. Scorpio is transformational as leaves are turning colors, falling to the ground, and nature is dying. Capricorn is winter-like, signifying when nature is maximally contracted, days are short, and austerity is required. 

Over time, zodiacal signs came to have additional meanings that went beyond their correlation to seasonal processes; yet (and this is a critical point), all such meanings were self-consistent with their original, root meaning in nature.


Stonehenge Solstice

Summer Solstice Sunrise at Stonehenge


It is difficult to summarize in a few sentences the immensity of data detailing how early humans organized virtually every facet of tribal life in conformity with the equinox and solstice points. Obsession with celestial correlates to equinox and solstice dates was so prevalent in the ancient world that it constituted a kind of human unanimity, being the central defining feature of ancient ceremonial monuments everywhere on earth, from the Inca’s Torreon in Machu Picchu, to the Mayan pyramid of Chichen Itza, the Bighorn Medicine Wheel and Sundance Lodge of the Plains Indians, Stonehenge in England, Newgrange passage tomb in Ireland, and the Great Pyramid of Egypt whose sides famously align with the four cardinal directions. At each site there is invariably a face, an aperture, a shaft, or some other means upon or through which the rays of the Sun exactly pass on the day of an equinox or solstice, thus heralding the changing of the seasons.

While the origins of zodiacal constellations predate recorded history, the bulk of Mesopotamian constellations were created within a relatively short interval around 1300 to 1000 BC. By 500 BC, the Babylonians had converted approximately 18 fuzzy, unequal constellations into 12 equal, sharply defined 30-degree sectors called zodiacal signs. At this time, signs and constellations were still conflated; constellation was sign, and sign was constellation.

The Babylonian zodiac was sidereal in the sense that planetary positions were determined in relation to the fixed stars of the constellations, BUT (and this is a big ‘but’) it was tropical in that the midpoints of the cardinal signs―Aries, Cancer, Libra, and Capricorn―were placed precisely at the equinoctial and solstitial points, as if anchored to them. The vernal equinox was at 15° Aries, the summer solstice at 15° Cancer, the autumnal equinox at 15° Libra, and the winter solstice at 15° Capricorn. From this, one might surmise an intention to associate specific constellations with specific seasons.


Cardinal Points

Due to Precession of the Equinoxes, the Cardinal Points Have Drifted into Previous Constellations


In fact, by the first millennium BC, there was virtually no difference between the Babylonian Calendar and the Babylonian Zodiac. Twelve months of 30 days became 12 signs of 30 degrees. That the sidereal zodiac was tied to the seasons is plainly evident in the fact that the first new moon closest to the vernal equinox in the constellation Aries started their calendar.

Bottom line, the equinoctial and solsticial points were all-important markers of temporal order. First the Babylonians determined their location in the sky, then built the zodiac around them. Just as ancient cultures built monuments around the cardinal points to commemorate the dates they occurred, so the cardinal points became the mighty frame for the entire zodiac structure.

Vernal Point is Now in Sidereal Pisces


Precession of the equinoxes is critical to our understanding of why the original zodiac bifurcated into two separate zodiacs. Precession is caused by the Earth’s wobble on its axis, which is induced by the gravitational tug of Sun and Moon. As a result, the Earth’s polar axis traces out a cone of approximately 26,000 years, which is how long it takes the vernal point to make a complete circle against the backdrop of the stars and return to a previous position. This means that the vernal equinox slowly drifts backwards through each constellation at the rate of 1° every 72 years.

The ancients displayed no technical or written understanding of precession until the 2nd century BC, and even then, it was not widely known or properly understood. For early stargazers, the constellations and earthly phenomena seemed to be in a fixed relationship to one another, as if attached by cosmic cables.

This cosmological feature was called durmahu by the Babylonians, which refers to a strong rope made of reeds that tied terrestrial seasons to celestial movements. As the Sun moved into a new constellation every month, so the seasons were pulled along like an ox pulls a cart―or, so it seemed.


Season Virgo

    Heliacal Rising of Sidereal Virgo Signals, “Harvest Wheat!”

With no awareness of precession or the actual cause of seasonal variations, early stargazers conflated constellations with their corresponding seasonal periods. If the constellation Virgo rose ahead of the Sun every year when wheat was ready to be harvested, so the ancients naturally equated that constellation with the harvesting of wheat.


Season Aquarius

Sidereal Aquarius and the Urn of Rain


If the rains in Babylonia fell in their greatest abundance in late winter and early spring, it was the god Aquarius in the heavens that controlled the rains. Aquarius’ overflowing vases were not regarded as simply a seasonal allegory of the rains, but the actual physical source of the waters that fell to earth.

However, in approximately 134 BC, the Greek astronomer Hipparchus checked the measurements of star positions by his predecessors. He noted that a certain star’s appearance in the dawn sky was drifting slightly forward century to century relative to the autumnal equinox. In fact, it was not the star that was moving, but the equinox that was drifting backwards.

Recall that at the beginning of the 1st millennium BC when the 12-sign zodiac was first constructed, the equinox and solstice points were set in the middle of their corresponding constellations―Aries, Cancer, Libra, and Capricorn. However, by mid-millennium, the vernal equinox had drifted to 10 degrees Aries. And when Hipparchus discovered precession in 134 BC, it had shifted to 5 degrees Aries.

The implication was staggering because it directly implied that the stars were not stable markers of the seasons and thus could not be relied upon for construction of accurate calendars over time. Seasonal predictability was the whole impetus behind calendar keeping, and calendar-keeping is the foundation upon which astrology rests.

Division of the year into 4 seasons with 3 substages was clearly wedded to the solstice and equinox points, the locations of which were thought to be anchored to specific stars in specific constellations. Yet, the cardinal points and cardinal constellations were slowly drifting apart.

Given the rate of precession, the cardinal points would eventually fall in constellations completely out of synch with earthly seasons and their requisite activities. If there was continuous slippage between the cardinal points and their corresponding constellations, the eventual mistiming of seasonal based activities, especially agriculture, was inevitable.

This led to Hipparchus’s decision to begin the zodiac with the vernal equinox, though there were precedents for this even before him. Subsequently, others followed. It had become obvious that the only way to keep the zodiac in synch with the seasons was to link it permanently to the cardinal points and abandon any reference to fixed stars. By separating the vernal point from the constellations and making it the official beginning of the zodiac, Hipparchus’s tropical zodiac did a better job of measuring time. Hence, it slowly gained prominence and superseded the older, less reliable constellational model.


Ptolemy (100 – 170 AD)

In Ptolemy’s monumental work, Tetrabiblos from the 2nd century AD, which summarizes the astrological tradition as it was handed down by his predecessors, he emphatically reports the consensus view that “the powers of the signs take their cause from the solstitial and equinoctial starting-places, and from no other source.”


By the 3rd century AD, it had become clear that zodiacal constellations never had the power to determine earthly phenomena that early humans projected upon them. The notion that constellations had power and meaning in themselves had merely been an illusion rooted in a misperception of the actual cause of seasonal processes.

From at least 2000 BC, as more sophisticated mathematical schemes evolved, constellations had been chopped, expanded, added, or eliminated, which only underscores that they never had any inherent meaning in themselves―that is, they were not gods with divine powers to determine events on earth as the ancients supposed. They were merely artificial constructs, expedient groupings of stars that served as a backdrop for measuring planetary movements and shifting phases of time, the causes of which were still not understood.


Angle Denotes Meaning

Angle Denotes Meaning


Note that signs in the tropical system are essentially angles carved out by the earth’s annual orbit about the Sun. Every 30 degrees from the vernal equinox constitutes a new sign. This same sequence of angles repeats itself with houses and aspects. They, too, are comprised of the same angles―0, 30, 60, 90, 120, and 180―and their meanings share a kinship with the signs to which they correspond. Again, signs, houses, and aspects are all based on multiples of 30 degrees.


Al Meaning Is An Angle

All Meaning Is An Angle


This is what gives us our system of rulerships. In astrology, all meaning is an angle; a phase within a more encompassing 360° cycle. Think about it: houses and aspects are completely unrelated to constellations; yet, they share a kinship of meaning with their corresponding signs. Libra, the 7th house, and the opposition are variations on a theme. Why? Because they’re comprised of the same 180° angle.

By all accounts, Hellenistic astrology was transmitted to India in the 1st and 2nd century AD and quite possibly earlier. It seems that all academic scholars who have specialized in the origins of astrology―Otto Neugebauer, Bartel van der Waerden, and David Pingree among them―agree on this point: India inherited most of its astrology from the Greeks. I am aware this is a controversial statement, especially here, and I cannot personally attest to its truth. I am simply unaware of any evidence to the contrary.

India did have an ancient system of 28 lunar Nakshatras analogous to constellations, which went back to at least the 3rd millennium BC. But prior to the 2nd century AD there was no zodiac in India of 12 equal, 30-degree divisions with four cardinal points. In fact, there was no zodiac at all. Once imported, however, the sidereal zodiac of India began with the constellation Aries, just as it did with the Hellenistic Greeks.

And up until the 5th century AD, Aries began with a fixed star that coincided with the vernal point at that time. Vedic scholar Dieter Koch asserts that the Puranas and other Vedic texts from 200 to 600 AD all state “the solstices are at the beginning of Capricorn and Cancer and the equinoxes at the beginning of Aries and Libra.”

Likewise, from approximately 2500 BC, the Nakshatras began with Krittika, which at the time coincided with the vernal equinox. Like the Babylonian constellations, the Nakshatra system appears to have originally been tied to the seasons, but over millennia have drifted out of synch with them. All of this suggests that early Indian astrology was consistent with both Babylonian and later Hellenistic formulations that recognized the central importance of the equinoctial and solstitial points as seasonal markers.

The problem was they had no knowledge of precession. This is evident in the fact that there’s no mention of precession in any Hindu astrological or astronomical text prior to the 10th century. 

What can we conclude from this?

It appears that Indian astrologers were simply following the sidereal tradition prior to Hipparchus and Ptolemy. Unlike their western and Arabic counterparts, they never grasped that the constellations had no intrinsic meaning or influence in themselves. And so Hindu astrologers continued to confuse the visible backdrop—the constellations—for the real thing.

So, to return to my original question: Is there a persuasive argument for claiming that constellational meanings originated independent of seasonal processes?

We know the original zodiac was a hybrid constructed of two factors: 1) invisible equinoctial and solstitial points that established the four seasons; and 2) constellations that provided visible markers for timing the 12 phases of year: four seasons of three months each. The original zodiac was a giant calendar-clock in the sky.

With Hipparchus’s discovery of precession, however, it became clear that the constellations had no causal relationship to events on earth. This was a momentous breakthrough, the importance of which cannot be overstated. For millennia, constellations had been the shiny object that distracted from the true importance of the equinoctial and solstitial points. But it was the latter, not the constellations themselves, which established the structure of the yearly cycle and the qualities of monthly durations.

And if constellations were not responsible for the seasons, it’s unlikely they were responsible for anything else either. All sign meanings are self-consistent and derivative of their foundational meaning rooted in nature. Once the foundational meaning of constellations was refuted, the whole system collapsed like a house of cards.

So, the umbilical cord was severed; the cardinal points were finally liberated from their entrapment in arbitrary, superfluous, made-up constellations. The old sidereal division of twelve fixed-star signs slowly fell into disuse both observationally and computationally―at least in the West.


Ghost of Sidereal Zodiac

Ghost of the Sidereal Zodiac


Yet, the sidereal zodiac hangs on, a vestigial organ once relevant to our Babylonian ancestors but no longer in accord with our current understanding of the cosmos. The sidereal zodiac was effectively terminated by the tropical zodiac, but like a ghost haunting its executioner, casts a troubling shadow over our profession.

In conclusion, let me simply say we should make room for diversity of opinion in astrology. But tolerance of opposing viewpoints is not mutually exclusive with critical thinking. A field grows by a willingness to question itself and go where the evidence leads. This is not always comfortable, but we astrologers are nothing if not resilient. I’ve every confidence we can survive and even grow stronger through rigorous self-examination.

Thank you very much.


  1. Kyösti Tarvainen, PhD

    Using the Gauquelin data, I have made a study on the house placement of the chart Ruler (the Ruler of the Ascendant) and a study on extroversion/introversion. Both studies gave statistically significant results. In both cases, it came into my mind to check whether the sidereal zodiac would work. It didn’t work. These studies will be published in Correlation.

    • Robert S Kimball

      Hello Dr. Tarvainen: I read with great interest your article in the newest edition of Correlation. I have to wonder how Vedic or Indian astrologers are reacting to your detailed research. Any defensive comments or criticism yet?

  2. charlene

    Love this ….. makes sense to me, I will read again …. great read.
    So! I think you set some new food out on the old banquet table, or is it the other way around…..hahahha anyway I was inspired to hit the books…..I have always enjoy your rhetoric….yes I still love you …….


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