The Origin of the Zodiac

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In a prior article, I discussed the history of the tropical zodiac. That article was centered on the research of historians of science. In this article, I look back to the origin of the twelve sign zodiac itself. In other words, I’ll be looking at the Babylonian zodiac. Like the article on the tropical zodiac, this one is intended to share some reliable historic information of interest with the general public. I hope you will find some interesting facts regarding the origin of the zodiac regardless of whether you believe in astrology.

Current State of Confusion

There is generally a lot of confusion as to the origin of the regular twelve sign zodiac, and why it split into sidereal and tropical zodiacs. I can recall my own past internet searches on the topic which had often ended in frustration due to a dearth of publicly available information. Even academic sources sometimes provide oversimplifications or ambiguities that lead to misunderstandings.

Tropical Zodiac Antiquity

As noted in the article on the tropical zodiac, the antiquity of the tropical zodiac tends to be misunderstood. For instance, it is widely thought that the tropical zodiac first came about in the 2nd century CE with Ptolemy’s Almagest. However, one of the most surprising aspects of zodiac history is that the tropical zodiac is nearly as old as the (Babylonian) regular zodiac itself. It was adopted by Greek astronomers in the late 5th century BCE, almost as soon as the zodiac became known in Greece. For more information about this see my article on the age of the tropical zodiac.

Number of Babylonian Zodiacal Constellations

Additionally, many believe there was a long historical use of a twelve constellation zodiac in Babylonian astrology prior to the advent of the regularized zodiac. As we’ll see the constellational zodiac of the Babylonians was one of 17-18 constellations (two were often condensed to one yielding 17). It was contracted into a twelve constellation zodiac after the zodiac was regularized. The regularization itself was due to calendrical influences. It is not the case that twelve constellations on the ecliptic particularly stood out for astrological use.

Calendar and Zodiac

What is most frequently overlooked in discussions of the zodiac is the important role the calendar played in influencing the decision to have 12 signs, 360 degrees, and Aries as the first sign. I have heard the tropical zodiac disparaged as just a fancy calendar. Such a statement belies ignorance about the important agricultural, cultural, and symbolic roles played by calendars in the ancient world. In fact, the advent of the twelve sign zodiac, especially the regular zodiac, is bound up with the calendar. An understanding of the close link between the zodiac and the calendar sheds light on some of the impetus and logic behind the zodiac.

The Myth

There’s a myth that is prevalent in the history of the zodiac. A convenient myth that makes for a nice simple explanation of the zodiac’s origins. The myth goes something like the italicized passage below.

The ancient Babylonians used the constellations that we still know today in their astrology. Twelve of their astrological constellations, those lying on the ecliptic, became the zodiac. Then as Babylonians became more concerned with mathematical astronomy, and less concerned with direct observation, they regularized the zodiac to 12 equal signs of thirty degrees. These signs roughly corresponded to the constellations they were named for. They were fixed relative to those constellations by a reference star and the zodiac was thus sidereal in both essence and calculation, without regard for the tropical relationship between the ecliptic and the equator. Much later, some Greek astronomers, most notably Ptolemy, opted to fix the signs relative to the equinox (intersection of ecliptic and equator), turning the zodiac into a sort of solar calendar. 

Missing Elements

Unfortunately for those who like simple and convenient theories, this myth betrays the very messy, complex, and fascinating true history of the zodiac. The myth does this through oversimplification and by ignoring the pivotal role of three extremely important elements.

First, it ignores the lack of sharp distinction between tropical and sidereal in the ancient world, where stars (sidereal) were regularly used as sign posts of the seasonal solar (tropical) year. Prior to knowledge of precession, the stars were the most readily apparent stellar sign posts of the tropical year. The Babylonians lacked knowledge of precession so they did not draw the sort of distinction between sidereal and tropical that we do today.

Secondly, it ignores the pivotal role played by the Babylonian idealized administrative calendar. That calendar was correlated with tropical features of the year as well as the phases and declinations of the fixed stars. It played a central role in Babylonian astrology and in shaping the zodiac.

Third, it ignores the fact that the zodiac was almost immediately imported into Greece where an explicitly tropical orientation was preferred from the start. Interestingly, that preference came prior to any knowledge of precession.

A Taste of Reality

Here is a taste of some of the facts betrayed by this myth.

Just prior to the regularization of the zodiac, the Babylonians were using a zodiac of at least 17 constellations, not 12. This was the constellational zodiac in use until roughly the time that the regularized 12 signs came into being. Its use was discontinued not long after the regularized zodiac arose.

The Babylonians had an administrative calendar of 12 months of 30 days each that was used since at least the end of the 4th millennium BCE. It is actually the oldest calendar attested in writing, being found in preliterate logographic cuneiform accounting texts. By the end of the 2nd millennium BCE, this calendar had become linked with the tropical/seasonal cycle through the phases of the fixed stars and variations in the length of day. By the time of the composition of the MUL.APIN (prior to 7th century BCE) it had become the central calendar for Babylonian astrology and astronomy. In the MUL.APIN, the most heavily copied text of Babylonian astrology, it is centrally featured throughout.

We’ll be examining these facts, and many more, in detail, with support from Babylonian texts and scholarly work in the history of science.


The origins of the Babylonian zodiac (and much of early astrology) are intimately linked with the agricultural year. Phases of the fixed stars relative to the Sun were used as significant markers of the agricultural year by ancient agricultural societies from Mesopotamia to Greece and beyond. The history of using the fixed stars as the yardstick for essentially tropical agricultural cycles long predates knowledge of precession or even the ability to accurately pinpoint the equinox.

The origin of the first 12 sign zodiac, with signs of 30 degrees, involved motivating factors that can be characterized as both sidereal and tropical. Its shape, regularity, and ratios are a direct result of the calendar rather than the stars. The Babylonian ideal calendar upon which it was based had a long standing tradition of correlation with the tropical year.

The use of sidereal periods and markers rather than tropical ones follows logically from their overtness and the Babylonian lack of knowledge of precession. With the stars as the long-standing yardstick for the tropical year and a lack of knowledge regarding their shift relative to the equinox, it is little wonder that longitudes should’ve been calculated by sidereal rather than tropical reference. Hence, we find the confusion wrought by a regular zodiac shaped by the calendar, correlated to the tropical year, named for the constellations, and measured by the stars, inevitably fracturing into tropical and sidereal counterparts.

What’s a Zodiac?

Before journeying to Babylon, let’s consider just what a zodiac is. Loosely defined, a zodiac consists of segments of the sky that the Sun, Moon, and visible planets appear to pass through. It is the segmentation of the “road” traveled by the Sun, Moon, and classical planets.

There are three major types of zodiac. These are constellational zodiacs consisting of groupings of stars, and two major types of regularized zodiac coordinate systems. Those two types are one fixed with respect to a reference star (sidereal) and one fixed with respect to the celestial equator (tropical). Additionally, the solar calendar can also act as a sort of proto-zodiac due to the correlation of solar declination and time of year with segments of sky by association with the phases of the fixed stars.

The Moon Among the Stars

Many cultures used and continue to use a zodiac of constellations. These are the constellations through which the Moon and planets travel. A couple examples include the twelve zodiacal constellations, as well as the 17-18 constellations in the Path of the Moon of the Babylonians. The number of constellations can vary, and constellations themselves vary in size and orientation. Traditional constellations also lack well-defined boundaries between them. Constellational references may include language about positions before, in, or after specific constellations, while sign reference refer only to positions within signs.

As stars become apparent at night, it is chiefly the passage of the Moon through the constellations which make the constellational shapes most significant. The precise ecliptic as defined by the passage of the Sun is not as significant. The Sun’s passage through whole constellations is not visible, though constellations which rise before sunrise were notable (see next section). We see this stress on the Moon’s position in a constellational zodiac in the ancient uses of the Indian nakshatras and the Babylonian constellations in the Path of the Moon.

The Sun and the Phases of the Stars

Ancient civilizations were agricultural. While the Sun’s passage through the constellations was not directly apparent, the phases of the stars with respect to the Sun were of the utmost importance.


Take for instance the first appearance of the bright star Sirius rising just before sunrise (after having been obscured by the Sun’s rays for about a month). This event initially heralded the flooding of the Nile for the Egyptians. The flooding of the Nile was crucial for Egyptian agriculture, so this event was closely monitored. It was used as the start of the Egyptian year. Interestingly, Sirius is displaced from the ecliptic such that precession has a small effect on the length of the year relative to Sirius, which was almost exactly 365.25 days. The fact that Egyptians compared their 365 day calendar year to the exact heliacal rising of Sirius may be one reason that Egyptians initially proposed the concept of the leap year (acted upon by Julius Caesar).

Off the Ecliptic

The phases of the fixed stars are neither dependent upon the form of the constellations themselves nor that the Sun pass through constellations (i.e. the stars don’t need to be on the ecliptic). However, they were used to divide the annual year of the Sun’s path and sometimes also the sky. As we’ll see, the Babylonians divided up the stars into 3 paths based on declination. Declination relates to the phases of the stars and the solar cycle (shape of the ecliptic). The phases of the fixed stars do not represent a type of zodiac, but their relationship with the solar year and thus the shape of the ecliptic, cause them to associate readily with the tropical year and its calendar.

Coordinates of Space

The two other types of zodiacs consist of signs rather than constellations. Signs are divisions of the belt of the ecliptic (the road of the Sun, Moon and planets) into regular segments (typically 12). These sign-based zodiacs double as coordinate systems with which one can specify the precise position of a planet with respect to the 360-degree ecliptic. For instance, a planet may be positioned in a specific one of twelve 30 degree segments or signs.

Sidereal and Tropical

There are two main different types of zodiacal coordinate systems, sidereal and tropical. A sidereal zodiac is defined with respect to a reference star. For instance, one could measure the distance between the Moon and the bright star Spica. A tropical zodiac is defined with respect to the celestial equator, and thus the solar year on Earth. The intersection of the ecliptic (solar path) with the equator (earth path) at the equinoctial points is the reference. For instance, we can measure the distance between the Moon and the point of the equinox where the ecliptic crosses the equator into the northern hemisphere (northern hemisphere’s Vernal Equinox).

It is important to note that there are many sidereal zodiacs, as different reference stars can be used. Still, all sidereal zodiacs are fixed relative to a reference star. Similarly, a tropical zodiac is not dependent on the exact starting point but that the starting point is fixed with respect to the celestial equator (i.e. point of equinox). For instance, as I noted in the article on the tropical zodiac, Geminos (1st century BCE) believed (wrongly) that the Babylonian zodiac was tropical, differing from the Greek zodiac only in that it started 8 degrees prior to the Vernal Equinox rather than at the Vernal Equinox.

Lunar and Solar Zodiacs

Interestingly, the sidereal zodiac is intimately related to the old observations of the Moon relative to the images of the constellations (observational omens). By contrast, the tropical zodiac is intimately related to the old observations of the phases of the fixed stars relative to the Sun and the calendar omen tradition (sign posts of the solar calendar).

As noted, the sidereal zodiac uses the stars as a reference. Stars were used as a reference system for tracking the Moon’s motion in the heavens, as she and the stars are most apparent by night.

The tropical zodiac is defined by the Sun, as the Sun’s apparent motion throughout the year defines the shape of the ecliptic. The cardinal points of the Sun cycle define the tropical zodiac and the agricultural/seasonal calendar year with its variation in the length of day and night.

In this way, there are real historical and natural links of the Moon to the sidereal zodiac and the Sun to the tropical one.


The concept of a zodiac with twelve equal signs emerged in the 5th century BCE before people knew that the sidereal and tropical points of reference could shift relative to each other. The Babylonian zodiac was a synthesis of an idealized calendar of 360 days with the (condensed) constellations. People were not aware that there could be a difference between a tropical and sidereal point of reference until a few centuries later, and even then only a small group of Greek astronomers were aware of the difference.

In the 2nd century BCE, the Greek astronomer Hipparchus discovered that the stars and the equinoctial points slowly shift with respect to each other, called precession. Unfortunately, his work on precession was not widely known until some time after Ptolemy popularized it in the 2nd century CE. For this reason, early astrological texts are often confusing when it comes to the tropical vs. sidereal issue.

Early Zodiac Riddles

Early astrologers, unaware of a difference between the two types of zodiac, often made statements implying use of one or the other at different points in the same texts. We see this in Babylonian astrology as well as in early horoscopic astrology (Hellenistic astrology).

For instance, Marcus Manilius (1st century CE) and Vettius Valens (2nd century CE) both used rising time schemes that entail zodiacal symmetry about the equinox. Such symmetry implies a tropical zodiac starting at the equinox. However, the zodiacal planetary longitudes in Valens’s text were clearly based on sidereal periods. In a prior article, I’ve shown that some of the signs Valens gave for planets in his own chart are actually different in the tropical zodiac.

Valens also evidently believed the equinox was at 8 degrees Aries of his zodiac. However, this was at a time when the common sidereal and tropical zodiacs almost exactly coincided. The zodiacal longitudes he used imply that the equinox would have been at about 1-2 Aries of his zodiac, many degrees off from the 8 degrees Aries position where he believed it was fixed.

Convenience and Ignorance

Examples like those in Valens clearly demonstrate a lack of knowledge of precession even in the 2nd century CE. In the absence of knowledge of precession, early astrologers believed the zodiac to be both tropically and sidereally fixed. This is true whether they placed the equinox at 0 Aries like the Greek astronomers or 8 Aries like the Babylonian ones. They relied on the tables available to them, which were by and large of the Babylonian tradition and sidereally based.

For these reasons, it is easy to see why such astrologers could use some figures, such as rising times, that imply a tropical zodiac. Also, they can make statements implying that the equinox is fixed somewhere in the zodiac that it hadn’t been for hundreds of years. Without knowledge of precession, there is no reason that they should’ve expected these statements to be puzzling to future readers. They were simply repeating inherited knowledge and using the available tables of the astronomers.

Conscious Choices?

Early zodiacal longitudes were clearly based on sidereal periods of the planets. Additionally, the oldest zodiacs are constellational ones, consisting of groupings of stars, such as the constellations in the Path of the Moon of the Babylonians. These facts bolster the view that the constellational sidereal zodiac is “the original zodiac”. However, a constellational zodiac differs in significant ways from a regularized sidereal zodiac. In a constellational zodiac, it is the specific stars and constellations that confer meaning, not segments and degrees.

The original use of constellations as an imagistic observational zodiac, and the use of specific stars as longitudinal reference points, is well-founded. However, the view that the stars were the motivating force behind the regular 12 sign zodiac is faulty. Additionally, the distinction between the positions of stars and the positions of days in the tropical year was a blurry one in the Babylonian tradition.

Calendrical Regularization

As we’ll see the 12 sign zodiac was largely motivated by an idealized 12 month calendar correlated with the tropical solar year. The 12 month calendar was a proto-zodiac for the Babylonians. It was associated with the seasonal year, declination of the Sun, and variation in day length (tropical elements).

The Babylonian zodiac was a fusion of the constellational zodiac of unequal constellations with the idealized regular 12 month solar calendar of equal months by a culture ignorant of precession. The advent of the regularized zodiac occurred in the context of a move away from observational astral sciences toward mathematical ones.

Awareness of Precession

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

The tropical zodiac is also the first zodiac to be consciously distinguished as tropical or sidereal by astrologers, beginning at least by the time of Ptolemy (2nd century CE). We currently lack evidence that prior to Hipparchus and Ptolemy there were any astronomers or astrologers aware of precession and choosing a sidereal orientation for a regularized zodiac. Therefore, the unconscious sidereal fixity of the Babylonian zodiac which started in the 5th century BCE should be contrasted with the conscious tropical fixity of the zodiac of the Greek astronomers later in that same century.

Part I: Fertile Lands, Fertile Skies

Much has been written about the close relationship between agriculture and the rise of cities. Most notable is Jared Diamond’s “Guns, Germs, and Steel” (originally published in 1997). Diamond showed how the ready availability of high-quality domesticable plants and animals and an east-west orientation (facilitating their transfer across similar latitudes), gave Eurasia (inclusive of northern Africa) a distinct head start in terms of technological development and lethal germ intimacy. That head start in turn led to their societies becoming dominant forces in much of the rest of the world.

As we’ll see the importance of calendrics for astrological societies encouraged close observation of the phases of the fixed stars. Therefore, the rise of mathematical astronomy in the land with the best potentially domesticable plants and animals (Mesopotamia) is no coincidence. By way of the phases of the fixed stars, the tropical year and the stars became intimately bound up together in the origin of mathematical astronomy.

The Agricultural Revolution

The agricultural revolution drastically transformed the human way of life. However, it was not a worldwide revolution that happened all at once. It occurred in different places at different times. Much of the world was without intensive agriculture until modern times and some areas still lack it. It also didn’t occur until roughly 7 million years after the appearance of the first hominids. Therefore, it is a rather recent development in human history. Humans are by no means farming animals by instinct.

“For most of the time since the ancestors of modern humans diverged from the ancestors of the living great apes, around 7 million years ago, all humans on Earth fed themselves exclusively by hunting wild animals and gathering wild plants, as the Blackfeet still did in the 19th century. It was only within the last 11,000 years that some peoples turned to what is termed food production: that is, domesticating wild animals and plants and eating the resulting livestock and crops.” (Diamond, 1997, p. 86)

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Agriculture and Specialization

Agriculturaly-based societies have a strong need for cooperation, specialization, hierarchy, accounting, and calendrics. In terms of social organization, hierarchy, based on a parent-child dynamic, and specialization, ensure that tasks get accomplished in a cooperative fashion by those who know best how to perform them. Accounting is important for making sure that workers are compensated and that goods are effectively distributed. Calendrics become important for coordinating the timing of annual activities and for logging work days and annual requirements of the state.

The surpluses of agriculture enabled the peoples of Mesopotamia, Egypt, and China to put division of labor to work for them. The surpluses of these early agricultural societies enabled the growth of specialization. Some of the forms of specialization most frequently highlighted by scholars include the scribe/record-keeper and the king/bureaucrat. It is hard to imagine how a society with a large population could possibly function without some means of record-keeping (writing) and political rule. A more easily overlooked specialization is that of the stargazing astrologer-astronomers. After all, today, we can quite readily accept that the functioning of society is not in any way dependent upon astrologers.

Fields of Stars

It is intriguing that most of the handful of early literate agricultural societies from Mesopotamia to the Mesoamerica, developed their own forms of astrological theory. While plant and animal domestication began in Mesopotamia about 11,000 years ago, it didn’t begin in Mesoamerica until at least 5,000 years later at the earliest (see Diamond, 1997, Ch. 8). Writing came later in both areas, and astrology even later.

It is telling that they both independently developed complex forms of astrology. They did so despite quite different cultures, starting points, and sets of domesticable plants and animals. Similar situations hold for the other early agricultural civilizations of Eurasia, such as Egypt and China. Why is it that early agriculturally-based societies with a means of record-keeping should turn their attention to closely tracking and recording the movements of the stars?

The Fertile Crescent

The earliest and most thoroughly studied of the ancient agricultural societies is Mesopotamia. Mesopotamia means the land between rivers, as it lies between the Tigris and Euphrates. It is appropriately nicknamed the Fertile Crescent. This area was not only the site of the first intensive agriculture and elaborate city complexes, but also the first writing and written astrology.

Multiple competing agricultural societies arose in the area. The most notable two groups were the Sumerians and the Akkadians of the southern half of the region. They were groups of people with distinct histories speaking distinct languages.

Why Mesopotamia?

Why was Mesopotamia the initial crux of the agricultural revolution? It is not that the area was simply more suitable for farming than other areas. California is very suitable for farming and has been occupied for 13,000 to 15,000 years. However, extensive agriculture did not arise in California until modern times. The answer pertains to the quantity of high quality domesticable plants and animals which are native to a region, particularly high-yield cereal grasses.

“Indeed, [the] worldwide survey of locally available large-seeded wild grasses […], and the worldwide survey of locally available big mammals […], agree in showing that all those areas of nonexistent or limited indigenous food production were deficient in wild ancestors of domesticable livestock and cereals.” (Diamond, 1997, p. 153)


For a detailed discussion of this topic, please see Diamond’s book, especially the chapter “Apples or Indians”. Diamond explains how the agricultural lifestyle is in competition with the hunter-gatherer lifestyle. Without significant incentive from very productive wild ancestors of domesticable crops and animals, experiments in domestication by hunter-gatherers occur very slowly or not at all. He details the immense domesticable plant and animal resources the people of Mesopotamia had at their disposal.

“Thanks to this availability of suitable wild mammals and plants, early peoples of the Fertile Crescent could quickly assemble a potent and balanced biological package for intensive food production. That package comprised three cereals, as the main carbohydrate sources; four pulses, with 20-25 percent protein, and four domestic animals, as the main protein sources, supplemented by the generous protein content of wheat; and flax as a source of fiber and oil […]. Eventually, thousands of years after the beginnings of animal domestication and food production, the animals also began to be used for milk, wool, plowing, and transport. Thus, the crops and animals of the Fertile Crescent’s first farmers came to meet humanity’s basic economic needs: carbohydrate, protein, fat, clothing, traction, and transport.” (Diamond, 1997, p. 142)

The Birth of Writing

Writing was originally an invention of the Sumerians in the late 4th millennium BCE. The Sumerians (in what is now southern Iraq) spoke a language which has no known relatives (it is an isolate). Their written language was initially logographic (one symbol per word) created by impressing a triangular or wedge-shaped (cuneiform) stylus into clay. The pictograms of this written system were used mainly for accounting purposes.

In the 3rd millennium BCE, this logographic script developed into a syllabic one (largely by means of the rebus principle). At that point the written language became much more robust, literacy became widespread in the region, and texts became richer. The Sumerian script was adopted by neighboring societies of Mesopotamia to write their languages as well, most notably Akkadian.

The rebus principle in action. Icons for concrete items like eyes and bees can be used to signify component sounds in the names of abstract concepts, such as the brand IBM.

Akkad to Babylon

Just north of Sumer was Akkad, home to the Akkadians, speakers of a Semitic language. Some of the more famous Semitic languages are Arabic, Hebrew, and Ancient Phoenician. Semitic is a subfamily of Afro-Asiatic which includes Ancient Egyptian and many languages of northern Africa and the Middle East. Akkadian would in time become a lingua-franca for the entire Near East.

In the 3rd millennium BCE, the Akkadians and Sumerians underwent extensive cultural contact to the point of widespread bilingualism. Akkadian eventually overtook Sumerian as the dominant language of the region by the 2nd millenium BCE. However, Akkadian retained much borrowed Sumerian in the language. The Akkadian ruler Sargon also briefly united Mesopotamia under one empire in 2334 (fell in 2154 BCE). Not long after its fall, there arose another brief empire of Sumerian speakers (Ur III; 2112-2004 BCE). That empire (Ur III) is particularly well-documented due to the survival of thousands of clay tablets with accounting records from the period.

Eventually two major Akkadian-speaking nations arose in Mesopotamia, Assyria in the north and Babylonia in the south. Some notable cities of Babylonia are its old Sumerian centers of Ur and Uruk. A small provincial town called Babylon was expanded under Hammurabi (18th century BCE) to eventually become the largest city in the world. It was around this same period (2nd millennium BCE) that we find our first evidence of an integrated theory of celestial divination, astrology.

Ancient Egypt and Mesopotamia c.1450 BCE

What is Babylonian Astrology?

Later we will look at the nature of Babylonian astrology, but for now let’s consider what is meant when we speak of this tradition in regional and political terms. What is typically referred to as Babylonian astrology is the tradition that began most clearly in the 2nd millennium BCE in Babylonia. It continued in the region (mainly Babylonia and Assyria) up until about the 1st century CE.

A Few Notable Changes of the Guard

It is important to note though that this regional astrological tradition was not always practiced under Babylonian political rule. The astrology was one of Mesopotamia, but primarily in Babylonia and neighboring Assyria. The most important surviving tablets are from about the 8th century BCE onward. Those tablets are believed to reflect a tradition going back at least to the mid 2nd millennium BCE.

From 911-619 BCE, Babylonia actually came under Assyrian rule (Neo-Assyrian Empire). Next it came back under Babylonian rule (Neo-Babylonian Empire; 626-539 BCE). Following that it was under the ruler of speakers of an Indo-European language, the Persians (Achaemenid Empire; ~539-333 BCE). The collapse of the Achaemenid Emire occurred as a result of Alexander the Great’s conquest in 333 BCE. It was then part of the Greek Seleucid Empire (~333-150 BCE). After that, it belonged to the Parthian Empire, also known as the Arsacid Empire (~150 BCE to 226 CE).

Indo-European Languages in the Region

Interestingly, the Persians, Greeks, and Parthians were all speakers of Indo-European languages. Persian and Parthian are much more closely related though as members of the same Iranian subgroup (written with Pahlavi).

Despite varying rule during the last half of the first millennium and beyond, the region remained a predominantly Persian area from the Persian conquest up until the Arab Muslim conquest of the 7th century CE. Also, despite being ruled by speakers of Indo-European languages in the latter period, important texts of the region continued to be written in cuneiform (in Sumerian-laden Akkadian) until about the 1st century CE.

Regional Trade

Trade across the Middle East and the Mediterranean thrived at varying points in Mesopotamian history. Societies were by no means isolated. At different points in time goods and ideas freely flowed between Mesopotamia, Egypt, Greece, and beyond.

I note that because this article will focus on Babylonian developments, but we cannot be sure all such developments occurred in a vacuum. The Babylonian zodiac was clearly exported to Greece within the century it first appears in cuneiform texts. The first horoscopic astrology (i.e. Hellenistic astrology) itself arose out of a synthetic mix of natively Babylonian, Egyptian, and Greek elements.

Significant Developments

The other important thing to note is that the astrology of the region underwent significant changes, particularly during the period of Persian rule (6th to 4th century BCE). The advent of the zodiac and the birth of a new more sophisticated mathematical astronomy in the region arose during those centuries when it was part of the Persian Achaemenid Empire. Additionally, the region was part of the Hellenistic world soon after these developments, during the time when it was in the Greek Seleucid Empire (~330-150 BCE) .

Unfortunately, even scholars sometimes too loosely lump together Babylonian astrology of say the 8th century BCE with that of the 3rd century BCE. The old cuneiform tradition did survive right on through to the 1st century CE. However, as noted, it underwent extensive change and development in the middle of the 1st millennium, especially in the 5th and 4th centuries BCE.

The developments included the introduction of the 12 sign zodiac, the ability to calculate planetary longitudes (ephemerides), a more abstract mathematical orientation, and the advent of personal horoscopy (individual birth charts). For this reason, it is important to distinguish early Babylonian astrology from late Babylonian astrology. We want to avoid projecting late developments backward in time as features that existed since the beginning of the tradition – an all too common mistake.

Early and Late Babylonian Astrology

Early Babylonian astrology can roughly be equated with the astrology of the regions of Babylonia and Assyria prior to the Persian conquest in the mid-6th century BCE. Late Babylonian astrology can be roughly equated with the astrology of the same regions from soon after the Persian conquest until about the 1st century CE. However, note that scholars often distinguish Late Babylonian astrology as starting about a century earlier (about 750 BCE), around the time of the MUL.APIN.

Early Babylonian astrology was not static. The most important work of Early Babylonian astrology, the MUL.APIN may represent a stepping stone from Early to Late Babylonian astrology. It continues the tradition of the late 2nd millennium BCE but with a couple changes and with a strong influence upon the later more mathematical tradition. Also, the reign of Nabonassar (747-734 BCE) saw an emphasis on keeping systematic astronomical diaries, which in turn enabled the discovery of sidereal periods for planetary phenomena. Later, we will be examining how an innovation of Late Babylonian Astrology, the 12 sign zodiac, was shaped by a notable feature of Early Babylonian Astrology, the 360 day calendar.

Nisaba: Goddess of Grain and the Scribal Arts

“… if any deity in the third millennium deserves credit for being interested in the stars it would be Nisaba.” (Koch-Westenholz, 1995, p.32)

Celestial omens started appearing in Mesopotamia near the end of the 3rd millennium BCE. I have noted how agriculture made cities, writing, and astrological record-keeping possible in the region. The Sumerian goddess Nisaba is of interest as her associations included agriculture, writing, the stars, and the calendar.

“The overall impression given by the Sumerian sources is that Nisaba was mainly concerned with the management of agriculture and the timing of activities that were dependent on the yearly seasons. The knowledge of astronomy (not astrology!) attributed to her was used to correct the vagaries of the lunar calendar.” (Koch-Westenholz, 1995, p. 33)

The Sumerian goddess Nisaba (goddess of writing) is depicted on this fragment of a chlorite vase. The name of Entemena, ruler of Lagash, is mentioned in the cuneiform text. c. 2430 BC. From Southern Mesopotamia, Iraq. The Pergamon Museum, Berlin, Germany.

Nisaba’s Tablet

How did Nisaba correct the vagaries of the lunar calendar?  It appears that she did so with the use of her tablet that had the stars of the heavens.

“She is said to measure heaven and earth, to know the secrets of calculation and, together with Suen, to “count the days”. She was associated in some way with the stars already in the Fara period. Her temple in Ereš was called the é-mul-mul, “House of the Stars”. Among many other tablets she had a lapis-lazuli tablet which is sometimes called the dub mul-an, “tablet with the stars of the heavens”, or dub mul-an-kù, “tablet with the stars of the pure heavens”.” (Koch-Westenholz, 1995, p. 32)

Nisaba was also worshiped by the Akkadians. The Akkadians and Sumerians added each other’s gods to their pantheons. Borrowing gods is commonplace among polytheistic cultures, including even in classical Roman times prior to the rise of Christianity.

Interestingly, we see Nisaba, her tablet, and a bright star associated with an Akkadian temple election in the 3rd millennium BCE. What is interesting is that the temple election text suggests the astrological use of the phases of the fixed stars as early as the 3rd milllennium BCE.

“In Gudea Cyl. A v 23 — vi 2 she is said to consult the tablet in order to tell Gudea with a bright star to begin the construction of Ningirsu’s temple.” (Koch-Westenholz, 1995, p. 33)

What, if any, is the connection between agriculture, accounting, issues with the lunar calendar, and tablets with records of stars?


Classics scholar, Daryn Lehoux, also touched on the riddle of Nisaba in his fascinating 2007 book, “Astronomy, Weather, and Calendars in the Ancient World: Parapegmata and Related Texts in Classical and Near Eastern Societies“. His work focuses on how “classical astronomy and astrology originate in techniques for weather prediction” (Lehoux, 2007, p. 26).

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Lehoux’s work fills a void as historians of science have tended to focus on the advent of sophisticated mathematical models of planetary motion as the start of their histories of astronomy. However, astrometeorology is an older tradition, still practiced to the present day (see your farmer’s almanac), and of more fundamental importance for agricultural societies.

“Since their calendars were at best of limited usefulness for the timing of seasonal activities, Greeks, Romans, Mesopotamians, and Egyptians all turned to the observation of the fixed stars in order to determine the best times for planting, harvesting, pruning, sailing, and more. This is because what are called the phases of the fixed stars are very closely tied to the agricultural season, and so are good indicators of when those seasons begin and end.” (Lehoux, 2007, p. 8)

Recalling the Greek Parapegmata

In my article on the origins of the tropical zodiac, I noted the importance of Greek and Roman astrometeorological texts from at least the time of Hesiod’s Works and Days.  The Greek Hesiod’s Works and Days (8th century BCE) and the Roman Virgil’s Georgics (1st century BCE) represent two famous early literary examples from those classical cultures.

“When the Pleiades, daughters of Atlas, are rising [in early May], begin your harvest, and your ploughing when they are going to set [in November]. Forty nights and days they are hidden and appear again as the year moves round, when first you sharpen your sickle.” (Hesiod, Works and Days, #383, Evelyn-White trans., 1914, p. 31)

“What makes the cornfield smile; beneath what star
Maecenas, it is meet to turn the sod
Or marry elm with vine”
(Virgil’s first lines of his Georgics, Rhoades trans., 1891, p. 3)

Fixed Stars in a Tropical Tradition

Many of the Hellenistic astronomers and astrologers played significant roles in the astrometeorological tradition. The parapegmata of the Greek geometric astronomers reveal a desire to fix the zodiac to the equinox from the time that the zodiac arrived in Greece. Still, the Greeks used the stars as the sign posts of the tropical year.

Geminos (1st century BCE) asserted that the tropical zodiac was the Greek way yet still presented a parapegma based on the phases of the fixed stars.  Ptolemy wrote his own literary parapegma on the Phases of the Fixed Stars despite being a conscious and explicit tropicalist with knowledge of precession. The Greco-Roman astrometeorological texts reveal that a desire to define the year and zodiac tropically was not incompatible with the use of the phases of the fixed stars as annual signposts. For more on this matter see the article on the origin of the tropical zodiac.

Phases of the Fixed Stars

As an aside let me briefly clarify what is meant by the phases of the fixed stars.

Heliacal Rising and Setting

A heliacal rising is an annual event. It occurs when a star first becomes visible in the east just before sunrise, after a period of being invisible (obscured by the Sun’s beams). The heliacal setting of a star is another annual event, which is the star’s last appearance in the west just after sunset, before it disappears behind the Sun’s beams. The time from heliacal setting to heliacal rising is about 30 days for stars near the ecliptic.

Achronycal Rising and Cosmical Setting

Acronychal rising (or evening rising) is when a star rises just after the Sun sets. It follows morning or heliacal rising in the sequence. It is followed by cosmical setting (morning setting) which is when it sets on the western horizon just before the Sun rises. Therefore the cycle is heliacal setting (evening setting), then heliacal rising (morning rising), then acronychal rising (evening rising), then cosmical setting (morning setting), then repeat. These are the most important phases of the fixed stars.

True Phases

Note that these heliacal phases are the apparent ones. There are also “true” heliacal phases which arose later and require calculation. True heliacal rising is when a star rises with the Sun exactly, which must be calculated. It can be difficult to tell whether a true or apparent rising is indicated in some later classical texts.


Lehoux notes that the stories of Nisaba indicate the use of astronomy to regulate the agricultural year. He also notes that some scholars have argued that the heliacal risings of fixed stars were used to regulate the calendar from a very early period.

The regular Babylonian civil calendar was a lunisolar one of 12 months. Each month was from first lunar visibility to next first visibility. The months alternated between 29 and 30 days in length, making for a year of 354 days, about 11 days short of the true solar year. It would require intercalation (insertion of an extra month) at regular periods to put it back in step with the seasons. The phases of the fixed stars could be used relative to the calendar to judge when intercalation was necessary.

However, there are some riddles pertaining to the early tablets listing the rising of the fixed stars. Often the early astrolabe texts, as they are called, seem to present a mythological ordering of the rising of fixed stars that is impossible in reality and could not have been used to correct the calendar. Therefore, the evidence for using the phases of the fixed stars to correct the calendar (determine when to intercalate a month) in the late 3rd and much of the 2nd millennium is not very robust. There is more evidence of intercalating the lunisolar calendar (of ~354 days) every three years, and sometimes even of neglecting to properly intercalate.

Mesopotamian Parapegmata?

Unfortunately, the Mesopotamians had no parapegmata in which the days of the year were all listed together with their corresponding significant annual astro-meteorological events. They did have a separate astrometeorological tradition though. Material similar to the classical astrometeorology of the Greek and Romans is seen in the most important text of early Babylonian Astrology, the MUL.APIN.

“Most similar to the classical parapegmata is a text called MUL.APIN, which has a list of schematic heliacal rising dates, and some seasonal meteorological predictions. It is certainly not a paragema, however, and the similarities between it and classical parapegmata are not close enough to warrant a claim of Mesopotamian influence. Nevertheless, MUL.APIN and other Mesopotamian texts do show that problems with timing annual climactic cycles were sometimes handled in analogous ways in Mesopotamia, Greece, and Rome, and this in itself is interesting as it points to similar sets of solutions to similar kinds of problems being found independently in these different cultures.” (Lehoux, 2007, p. 101)

Beyond Nisaba’s Time

The way in which Nisaba’s star tablet was used to correct the vagaries of the calendar way back in the 3rd millennium BCE is still shrouded in mystery. The use of a tablet of star information to help correct the lunar calendar with respect to the solar year and aid the administration and accounting of an agricultural empire logically evokes the use of paragegmata in classical Greek and Roman society. However, the early Babylonian astro-meteorological tradition is rather messy and full of mysteries.

On the other hand, the associations between agriculture, writing, the stars, and the calendar are not mysterious. Their strong relationship becomes much more apparent in the influential texts of the late 2nd and early 1st millennium. When one looks at the administrative calendar and its role in early texts, these connections become clear. By the time of the MUL.APIN, the phases of the stars definitely did play a role in adjusting the lunar calendar with respect to the solar year.

“The Mesopotamians also used the phases of the fixed stars as indicators of weather patterns, and stellar phases played an important role in the so-called Uruk scheme, which regularized their lunar calendar with respect to the solar year.” (Lehoux, 2007, p. 10)

Part II: Babylonian Stars

So far, we’ve seen that the distinction between tropical and sidereal was blurred for ancient agricultural societies. The phases of the fixed stars acted as relatively reliable sign posts of the tropical solar year. Even among tropicalists like Ptolemy, who were fully aware of precession, correlating the year to the phases of the fixed stars was viewed as valuable.

We saw that for the Mesopotamians there was a similar astrometeorological tradition of correlating the phases of the fixed stars to important points in the seasonal (tropical) year.


The MUL.APIN is a very important source for the use of the fixed stars in early Babylonian astrology.  Through the MUL.APIN we gain much greater clarity as to the strong Babylonian relationship between the fixed stars and the tropical year.


It is interesting in the context of our discussion of the relationship between agriculture and astronomy that the name MUL.APIN is itself a compound of MUL and APIN, the Sumerian words for “star” and “plough” respectively. The plough star is the first star mentioned in the work, identified with Enlil, and leading the stars in the path of Enlil.

Enlil was the chief deity of the Sumerians. Enlil is the god of wind, air, earth, and storms, but is also the patron of agriculture. One of the main symbols for his son, Ninurta, is the plough.

The plough star is actually a constellation that resembles a plough. The constellation is composed of our modern Triangulum, presumably the pough’s body, plus Gamma Andromedae, presumably its handle. The path which it leads, that of Enlil, is composed of the stars of northern declination, such that the Sun is in the path for the quarter of the year that is divided by the Summer Solstice.

The Sun’s journey through the path of Enlil is from approximately 45 days before the solstice until 45 days after it – the peak of the year. The Plough’s heliacal rising was much earlier in the year, in February, and marked the time to begin spring ploughing.


The oldest tablet fragments of the MUL.APIN date to the late 8th or early 7th century BCE. However, the composition for the original text has been assumed to be about 1,000 BCE or earlier. Additionally, work on dating the text according to the star lists in the work favors the view that it is based on observations that took place around 1,300 BCE, give or take 150 years (see De Jong, 2007).

Definitive Edition

A definitive new edition and translation of the MUL.APIN, with extensive commentary was published in 2018 by Hermann Hunger and John Steele. Their edition is highly recommended. As they say in their introduction, the MUL.APIN is arguably the most important work of Babylonian astronomy. It compiled a long-standing tradition and strongly influenced later developments.

“The text known as the MUL.APIN was the most widely copied work in the astral sciences written in ancient Mesopotamia. It was composed sometime before the end of the eighth century BC, and copies of it have been found at many sites throughout Assyria and Babylonia, dating from the late Neo-Assyrian (eighth to seventh century BC) down to the Seleucid (third to first century BC) periods. In addition to being widely copied, MUL.APIN was clearly read and used by scholars throughout these periods: it is one of only a few works of astral science identified by name in other cuneiform texts and provided the foundation for many later texts of what we term ‘schematic astronomy’. It is no exaggeration to say, therefore, that MUL.APIN was the most important work of Babylonian astronomy.” (Hunger and Steele, 2018, p. 1)

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Elements of Early Babylonian Astral Science

In their introduction, Hunger and Steele identify some of the significant feature of early Babylonian astronomy and astrology (astral science).

“…it is possible to identify several themes within early Babylonian astral science: the use of simple numerical schemes to model the variation of the length of day and night; the grouping of stars into three ‘paths’ associated with the gods Enlil, Anu, and Ea; the development of collections of celestial omens; and the use of the 360-day schematic calendar.” (Hunger and Steele, 2018, p.11)

The collections of celestial omens tend to be the focus of most treatments of Mesopotamian astrology. However, the models for the length of day, the groupings of the three paths of the stars, and the use of the 360-day schematic calendar also relate to the omens. Furthermore, these are the elements of Babylonian astrology that most strongly reveal the Babylonian preoccupation with the tropical year. For now, let’s take a look at the three paths of the stars, as well as some other special Babylonian collections of stars. Later, we’ll take a much closer look at the schematic calendar.

Three Paths of Stars

The MUL.APIN starts with a catalog of the stars (most of which are actually constellations) which will be used in the rest of the text, arranged into three lists. The stars/constellations in those three lists represent the full repertoire of stars of the text. The grouping of the stars into the three lists pertains to the paths of the gods Enlil, Anu, and Ea and is a very traditional Babylonian grouping.

“The grouping of stars into three categories, those of Enlil, Anu, and Ea, follows a tradition that can be traced back to at least the middle of the second millennium. A Middle Babylonian prayer to the gods of the night from Boghazkoi … contains a list of stars in order of their first appearances, followed by a reference to the stars of Ea, Anu, and Enlil.” (Hunger and Steele, 2018, p. 170-171)

The Sun’s Journey Across the Paths

As noted in the above quote, the phases of the stars (order of appearance) was related to the three paths since at least the middle of the second millennium. Additionally, by the time of the MUL.APIN, the Sun’s motion over the course of the year was also correlated with the three paths.

“The three groups of stars, those of Enlil, Anu, and Ea, can be associated with the three ‘paths’ (harranu) of Enlil, Anu, and Ea mentioned elsewhere in MUL.APIN (II Gap A 1 – II Gap A 7, which describes the Sun’s motion among the three paths over the course of the year …). The three paths also occur in celestial omens and occasionally in accounts of observations.” (Hunger and Steele, 2018, p. 171)


The path of the Sun over the course of the year (i.e. shape of the ecliptic) naturally corresponds to the paths of the stars due to the fact that three paths are based on declination. Declination pertains to the distance of an object north or south of the equator.

The Sun’s tropical cycle (i.e. shape of the ecliptic) is also a function of its distance north or south of the equator. Where the Sun (and hence ecliptic) crosses the equator is an equinox, while where the Sun (and hence ecliptic) reaches its greatest declination is a solstice. Therefore, a division of the stars based on bands of declination readily correlates with the Sun’s annual tropical cycle.

The tropical cycle defines the ecliptic with respect to the celestial equator while the sidereal cycle disregards the celestial equator. A division based on declination is a division which emphasizes the primacy of the celestial equator.

“The stars in the three paths fall roughly into three regions of declination: the Enlil stars to the north of about +17° declination, the Anu stars to between +17° and -17° declination, and the Ea stars to the south of about -17° declination.” (Hunger and Steele, 2018, p. 171)


Celestial Sphere with Ecliptic in Red
Paths and the Calendar

The MUL.APIN correlates a 360 day calendar (more on this in the next part) with the Sun’s motion across the three paths over the course of the year. The text also explicitly correlates the calendar with the length of day and night over the course of the year and the positions of the equinoxes and solstices. Therefore, the fixed stars, categorized by relative distance from the equator, are correlated with a calendar that takes into account the length of day, the equinox/solstice points, and solar declination. This illustrates the strong relationship between the stars and tropical solar year in early Babylonian astrology.

“The Babylonians divided the fixed stars into three groups: the stars of Anu, Enlil and Ea.’ To which group they belonged depended, for most of them, on where they rose on the Eastern horizon. The horizon was divided into the Paths of Anu, Enlil and Ea. The Path of Ea lies to the north, Anu is in the middle, and Enlil lies to the south. The boundaries between the Paths may be gleaned from the ideal calendar of Mul.apin II (Hunger and Pingree, Mul.apin p. 88 f), according to which the sun stands in:
— the Path of Anu from the 1st of Addaru (XII) to the 30th of Ajjaru
(II) (azimuth of the sun 290°-250°)
— the Path of Enlil from the 1st of Simanu (III) until the 30th of Abu
(V) (azimuth of the sun 250°-240°-250°)
— the Path of Anu from the 1st of Ululu (VI) to the 30th of Arahsamnu
(VIII) (azimuth of the sun 250°-290°)
— the Path of Ea from the 1st of Kislimu (IX) to the 30th of Sabatu (XI)
(azimuth of the sun 290°-300°-290°).” (Koch-Westenholz, 1995, p. 24)

The calendar is explored in more detail in the next part of this article.

Correlating Phases with Day Length Schemes

One notable and particularly striking feature of lists of approximate phases of fixed stars in the MUL.APIN is the inclusion of day and night lengths at the time that the phases occur. I provide an example below.

“On the 15th day of Month IV, the Arrow, the Snake, and the Lion become visible; 4 minas is the watch of the day, 2 minas is the watch of the night.” (MUL.APIN, I ii 42-43, Hunger and Steele trans., 2018, p. 137)

Note that passages like this correlate the phases of the fixed stars with the ideal 360 day calendar and the length of day at that point in the year. All of these things are approximate in the MUL.APIN. As noted, the MUL.APIN is not a parapegma. It expresses the phases of the stars in 5 day intervals of the idealized calendar, and it uses a rough scheme for figuring the length of day. A ‘mina’ is a weight measure, as the Babyonians are referring to the amount of water used by a water clock over the course of a day or night.

Equinox on an Idealized Full Moon

In the schematic calendar, one ideal is for the Full Moon to occur on the 15th of the month, as the Full Moon marks the 15th of each month in the normal civil Babylonian lunisolar calendar. For instance, the following passage expresses that the Full Moon on the 15th of the first month also marks the equinox, with the Moon in Libra, Sun in Aries, and day and night being equal.

“On the 15th day of Month I, the Moon stands in the evening within the Scales in the East, and the Sun in the West in front of the Stars behind the Hired Man. 3 minas is the watch of the day, 3 minas is the watch of the night.” (MUL.APIN, II i 19-21, Hunger and Steele trans., 2018, p. 145)

The Arrow and the Summer Solstice

Another list of stars from the first section of the MUL.APIN pertains to time intervals between two stars rising. It starts and ends with the star or constellation, the Arrow (Sirius, probably with some stars of Canis Major). In their commentary, Hunger and Steele note that the Arrow is used to start the list because its heliacal rising was correlated with the Summer Solstice.

“[…] the total number of days going around the circuit, from the Arrow to the Arrow again, is 360 days, as it should be in the schematic calendar. As discussed […], the Arrow’s first visibility is placed on the date of the summer solstice in the schematic calendar. This almost certainly explains why the list begins with the Arrow, rather than with the Hired Man, as in Section I ii 36 – I iii 12. The summer solstice, rather than the beginning of the year, was often taken as the beginning point of numerical schemes in other texts of schematic astronomy.” (Hunger and Steel,e 2018, p. 186)

Images and Markers

The 17-18 constellations in the Path of the Moon played a significant role in shaping the Babylonian zodiac. The influence is especially apparent in terms of the names of the signs and their imagistic associations. Aside from the use of the constellations in the Path of the Moon, certain bright stars (Normal Stars) in that path were used as markers for phenomena. Both the use of Normal Stars and the stars in the Path of the Moon are attested from at least the 8th century BCE.

Normal Stars

Observational positions of the Moon and planets were given by Babylonians with respect to the Normal Stars. The Normal Stars were 31 bright stars near the ecliptic. In Late Babylonian astrology such normal star positions could complement positions given from zodiacal ephemerides. However, Normal Star positions were often estimated, rather than measured, positions. Observations of planets relative to the Normal Stars are believed to have been used to establish the sidereal periods of planetary phenomena which made possible the ephemerides of Late Babylonian astrology.

The Diaries

To get some idea of the way that Normal Stars are used, please see some of the Babylonian “Diary” texts which recorded planetary positions at important points. The Diary texts are comprised of systematically recorded observations initiated during the reign of Nabonassar (747-734 BCE).

“The Diaries typically contain for each month: a statement of the length of the preceding month; the time interval between sunset and moonset on the first day of the month; time intervals between sun/moonrise/set in the middle of the month; the time interval between moonrise and sunrise on the morning of the moon’s last visibility; the dates on which the moon approached the various Normal Stars […] and the watch of the night which this occurred; and the date and description of lunar and solar eclipses. For the planets they record dates and position among the stars of first and last visibility, direct and retrograde motion and stationary points, and conjunctions with Normal Stars. The relation of the moon and planets to the Normal Stars is expressed in terms of ‘cubits’ (about 2.5°) or ‘fingers’ (about 5′) above (north), below (south), in front (west) and behind (east); but although the general sense of these statement is agreed, comparison with modern calculations suggests that the positions were often estimated rather than measured.” (Britton and Walker, Walker ed.,1997, p. 50)

Stars in the Path of the Moon

While Normal Stars were used for early positional reckoning in the sky, the constellations in the Path of the Moon were not. They make their first appearance around the same time and are noted in the MUL.APIN.

“The gods (var. stars) who stand in the path of the Moon, through whose region the Moon during a month passes repeatedly and keeps touching them: The Stars, the Bull of Heaven, the True Shepherd of Anu, the Old Man, the Crook, the Great Twins, the Crab, the Lion, the Furrow, the Scales, the Scorpion, Pabilsag, the Goat-Fish, the Great One, the Tails of the Swallow, Anunitu, and the Hired Man.” (MUL.APIN, I iv 31-37, Hunger and Steele trans., 2018, p. 143)

The MUL.APIN then continues to specify that the Sun, Jupiter, Venus, Mars, Mercury, and Saturn also travel that same path and that concludes the first part of the text.

Seventeen constellations appear to be mentioned, though the tails and the swallow are sometimes separated into two constellations (yielding eighteen) as the actual text is somewhat ambiguous. Hunger and Steele (2018) argue that evidence from the star lists of the MUL.APIN and from other uranology texts support the view that the Tails are part of the Swallow, rather than an eighteenth constellation.

The list begins with the “Stars” which is the Pleiades. They are first because the heliacal rising of the Pleiades was believed to roughly coincide with the start of the year. These stars in the Path of the Moon contain most of the later 12 zodiacal constellations, as well as pieces of the rest. For instance, the Pleiades and the Bull of Heaven combined to form the later final form of Taurus.

19 Zodiacal Constellations?

Various Uranology texts sometimes contained additional zodiacal constellations. There were at least 19 zodiacal constellations in total used by the Babylonians in their texts.

“Observational texts from the seventh century BC onwards include reports of the position of the moon and the planets relative to the zodiacal constellations or individual stars or small star groups within those constellations (e.g. the Front Star of the Head of the Hired Man). These texts add one further zodiacal constellation to the list of zodiacal constellations: the Chariot. Astrological texts from the same period attest to one further zodiacal constellation: the Field. Thus, at least nineteen zodiacal constellations were identified by the Babylonians (see also Ratzon, 2016).” (Steele, 2018, p. 98)

Naming Signs

When the regular zodiac arose in the 5th century BCE, one method of naming the signs pertained to constellations associated with the months those signs were correlated with. There are actually three means of naming the signs in early zodiacal texts. Either the month name was used, the number of the sign (starting with Aries as I), or the name of a constellation occurring in that sign.

As multiple constellations were initially associated with any given one sign, still over a hundred years after the advent of the regularized twelve sign zodiac, alternate names for signs based on constellations occurred. For instance, for some time, it was more common to refer to the sign Taurus as “the Stars” (Pleiades) rather than “the Bull” (Taurus).

“[…} the process of choosing which twelve constellations to use was not straight forward. Furthermore, it is clear that alternate names for some of the signs of the zodiac were still in use in the early third century BC, well over a hundred years after the zodiac was developed.” (Steele, 2018, p. 101-102)

Steele’s recent (2018) paper on the development of the zodiac explores the development of the constellation-based name for each sign in some depth, so I highly recommend it. This naming process provides the best evidence that the concept of the twelve signs actually preceded, rather than followed, the concept of twelve constellations spanning the ecliptic. Now, let’s turn to why we ended up with 12 signs in the first place.

Part III: From Calendar to Zodiac

The motivation for twelve signs comes from the Babylonian schematic calendar of 12 months of 30 days (360 days). It is the oldest attested calendar, originally used for accounting purposes. That calendar came to be the main calendar of Babylonian mathematical astronomy and astrology, associated with the phases of the fixed stars, tropical year phenomena, and certain types of omens. When constellations began to be correlated with months, a new system of measuring longitude arose based on the division of the ecliptic into twelve segments.

Emergence of the Zodiac

The twelve sign zodiac did not emerge until the 5th century BCE. It becomes most evident in the late 5th century BCE, with inklings of its use earlier in that century.

“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)

“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)

Twelve from the Calendar

Scholars, since at least Isaac Newton’s time, have known that the division of the ecliptic into 12 signs and 360 degrees was due to the influence of the calendar.

“All nations, before the just length of the Solar year was known, reckoned months by the course of the moon, and years by the returns of winter and summer, spring and autumn and in making Calendars for their Festivals, they reckoned thirty days to a Lunar month, and twelve Lunar months to a year taking the nearest round numbers: whence came the division of the ecliptic into 360 degrees.” (Isaac Newton from “The Chronology of Ancient Kingdoms”, 1728, p. 71)

“It is generally agreed among historians of Babylonian astronomy that the concept of the zodiac as a uniform division of the band through which the sun, moon and planets move into twelve equal parts, each of which was further subdivided into 30° developed by analogy with the division of the schematic year into twelve months, each of which contains 30 days (Stephenson et al., 1995; Brack-Bernsen and Hunger, 1999; Brown, 2000; Steele, 2007; Britton, 2010).” (Steele, 2018, p. 100)

Aries and the Equinox

Additionally, the decision to start the zodiac with Aries was also based on the fact that the vernal equinox occurred in that corresponding constellation and pertained to the start of the Babylonian year.

“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 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)

Multiple Constellations Per Sign

Leading up to the zodiac, there were constellations associated with months of the year.

“Progress towards the eventual system of zodiac signs is indicated by a Babylonian text of about the fifth century BC which lists the 12 months (ignoring the intercalary month) and their associated constellations, but assigns both Pleiades and Taurus to month II, both Orion and Gemini to month III and both Pegasus and Pisces to month XII. The final system of twelve zodiac signs of 30° first appears around the middle of the fifth century BC.” Britton and Walker, Walker ed., 1997, p. 49)

As noted above, even after the zodiac came into being multiple constellations were still associated with the signs for some time. This is evident from the fact that there were alternate names for signs based on the constellations found in those signs.

Calendar as Proto-Zodiac

These facts about the influence of the calendar on the zodiac have been known for some time, but are ill-understood by the public. Part of the confusion pertains to the 360 day calendar. Very little information is publicly available on the use of the 360 day calendar and the concept appears to be quite counter-intuitive. However, the 360 day calendar is fascinating and its study is essential to really understanding the motivation for a 12 sign regular zodiac.

The Lunisolar Calendar

Search for information on the Babylonian calendar and you will find information on their lunisolar calendar. This was the main calendar used in daily life. In that calendar, a new month begins with the first visibility of the Moon, which is about every 29.5 days on average. The months alternate as 29 and 30 days in length, yielding a year of 354 days.

Traditionally, the year starts with the new month near the equinox. Originally, it was the new month after the equinox, such that the equinox was associated with the full moon of the 15th of the last month (XII). By the time of the MUL.APIN, the year began with the new month preceding the equinox, so the equinox itself was associated with the Full Moon (15th of the month) of the first month. However, the actual location of the equinox would vary year-to-year within about 30 days of the start of the year. As this calendar is 354 days long, it required that an extra month be inserted (intercalated) about once every three years to put it back in line with the solar year.

Lunisolar Approximation?

The lunisolar calendar is attested since at least the late 3rd millennium BCE. Many (for instance, Newton in the quote above, as well as Lis Brack-Bernsen) believe it was in use even prior to the schematic 360 day calendar. Still, the schematic calendar is the first attested calendar by far. The belief that the 360 day calendar arose because of the lunar calendar is a position based on reasonable presumptions rather than textual evidence. It is presumed that a year of 12 months of 30 days came about as an approximation of the lunisolar calendar, and thus was derived from it.

Hebrew Calendar

The Hebrew calendar was borrowed from the Babylonians (during their 6th century BCE captivity). For this reason, we still see the use of the Babylonian lunisolar calendar (with some adaptations) in the Jewish tradition. For instance, Passover typically falls on the 15th of the first month of the year in the Hebrew calendar, as New Moon prior to the Vernal Equinox typically starts the year (1st) and the Full Moon would fall on the 15th.

I recommend taking a look at the Hebrew calendar to get a feel for the way the Babylonian lunisolar calendar would function. Similar calendars are also still used in some other Middle Eastern societies.

The 360 Day Calendar Emerges

In contrast to the lunisolar calendar, information regarding the 360 day calendar is relatively hard to come by. This is despite the fact that the first attested calendar in written records is the 360 day calendar, 360 day calendars were actually quite widespread, and the 360 day calendar was the most important calendar for Babylonian astrology and astronomy.

A very good source of information on the historical Babylonian use of the 360 day calendar is Lis Brack-Bernsen’s “The 360-Day Year in Mesopotamia” found in the 2007 “Calendars and Years” edited by John M. Steele.

The calendar may variously be referred to as the schematic calendar, ideal calendar, or administrative calendar.

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Early Origins

Evidence for the 360 day year is actually found in the preliterate early logographic accounting texts of Uruk from the late 4th millennium BCE. This makes the 360 day calendar the first textually attested calendar. 

“Archaic texts from Uruk (3200 BC-3000 BC) concern centralized bookkeeping. They document the same artificial diffusion of the year into 12 months of 30 days each that we know from later periods.” (Brack-Bernsen, Steele ed., 2007, Loc. 2534)

Both it and the lunisolar calendar were used by the peoples of the region, sometimes together in the same texts, from the Old Babylonian period to about the common era. However, as I’ve noted, the lunisolar calendar is not attested prior to about the mid-3rd millennium BCE.

“We conclude that the continuous and parallel use of the two calendar[s] has been shown all way through from 2600 BC to 2100 BC, while in the archaic texts, only the administrative calendar is clearly demonstrated.” (Brack-Bernsen, Steele ed., 2007, Loc. 2566)

The 360 Day Calendar in Odd Places

Likely due to diffusion, many ancient societies of Eurasia used such a 360 day calendar, including but not limited to the Old Persian calendar, original Egyptian calendar, and a scheme found in the Indian Rig Veda. More fascinating is its independent occurrence in Mesoamerica. It also appears to have influenced the concept of prophetic timing in the Biblical tradition.


Mesoamericans came to the progression of agriculture, cities, writing, and astrology much later and wholly independently. Interestingly, they also developed a 360 day calendar.

A tun was an approximation to the true solar year and so 18 twenty-day intervals, rather than 20, were built into the sequence. The Maya chose to use 360 instead of 365, and their reason most likely was the numerological usefulness of 360. It can be divided and manipulated in many ways.” (Krupp, 1983, p. 186)

The Prophetic Year

One of the more fascinating uses of the 360 day calendar pertains to Biblical prophecy. The prophetic year is typically defined as a 360 day year, a 360 year period, or a 360 year period of 360 day years. Its use is implied by passages in the Book of Genesis (7:11, 7:24, 8:4), the Book of Daniel (7:25, 9:27, 12:7), as well as the New Testament’s Book of Revelation (11:2, 11:3, 12:6, 12:14, 13:5). The prophetic year concerns the duration or timing for some event foreseen by a prophet to take place

Abraham and Zodiacal Releasing

The use of the 360 day year in the context of Jewish prophecy is interesting, as it relates to a Hellenistic astrological technique attributed to an astrologer named Abraham. Vettius Valens (2nd century CE) presented a timing technique (today called zodiacal releasing) which he attributed to an astrologer Abraham. The use of the name Abraham implies an astrologer of Jewish heritage. This technique did not use the typical 365.25 day year of the Alexandrian calendar which Valens used for most other techniques. Rather, it used a year of 360 days. Therefore, zodiacal releasing may represent an instance of the prophetic year in use.

Valens also used a 360 day year for another technique called decennials. I do not know of a Jewish connection to that technique.

Note on Conspiracy Theories

Some conspiracy theorists speculate that such 360 day calendars may have accurately reflected a solar year that was actually 360 days in length. However, the year has only been slowing by about 2 milliseconds per century (1 second every 50,000 years), so that hypothesis is not sound.

Isaac Newton appears to have captured the main motivation: to have a nice round number to work with. 360 is divisible by many numbers and is an ideal year to use for accounting and administration. However, it is also interesting that the actual mean between the lunar year of 12 Moons and the solar tropical year is about 359.8 days, making 360 days the mean lunisolar year within a fifth of a day.

Babylonian Use of the 360 Day Calendar

As I noted, the 360 day calendar was originally used for centralized state accounting. Later, it was still used for accounting and in scribal education (i.e. in mathematics). However, in later periods it is less attested for accounting after it becomes more associated with astronomy and astrology.

“Analysis of Ur III work rates, Old Babylonian coefficient lists, and Old Babylonian mathematical texts have thus shown that accounting practices involving the artificial year of 12 x 30 days in either administrative or scribal training contexts are found throughout the time from Ur III to the Old Babylonian period. And from this time onwards, we have evidence for the utilization of the artificial 360-day year in “astronomical” texts”.” (Brack-Bernsen, Steele ed., 2007, Loc. 2682)

Initial Astronomical Use

The schematic calendar became associated with astronomical regularities in the Old Babylonian period. This is the period of the early 2nd millennium BCE (20th to 16th centuries BCE). Already by the Old Babylonian period, the schematic calendar was also associated with day length schemes and the positions of the equinoxes and solstices.

“Already during Old Babylonian times, the schematic year of 12 months of 30 days was used for recording astronomical regularities. The Old Babylonian text BM 17175+17284 contains a scheme that connects day length and season (time within the year). The text places solstices and equinoxes on the 15th of Months XII, III, VI, and IX and the day length varies linearly between 2 minas and 4 minas.” (Brack-Bernsen, Steele ed., 2007, Loc. 2682)

An Ideal Calendar

The 360 day calendar is sometimes called the ideal calendar. It was indeed conceived as reflecting the ideal. When nature conformed to the schematic calendar it was viewed as a positive portent.

“In the astronomical/astrological compendia Enūma Anu Enlil tablet XIV and MUL.APIN, a so-called “ideal” or “schematic” year of 12 x 30 days is used. Omen texts, letters and reports show that it was interpreted as a good omen when a new month started on day 1 […]. Obviously, it was taken as a good sign when nature behaved as the “ideal” 360-day year and a bad sign when nature deviated from the “ideal calendar”. […[ the “ideal calendar just is a continuation of the artificial year of accounting.” (Brack-Bernsen, Steele ed., 2007, Loc. 2598)

Also recall what I noted above about the 15th day of the month of the ideal calendar’s association with the Full Moon. The Full Moon is the 15th in the lunisolar calendar, so ideally the equinoxes and solstices would occur on the Full Moons of their associated months.

Calendar Omens

The 360 day calendar was used in relation to many omens pertaining to specific days of the year. Some omens that were originally associated with calendar dates in the ideal calendar even became associated with zodiacal degrees in later zodiacal texts.

“The two texts have an older parallel in STT 11 300, 2 which assigns the under-takings and incantations to calendar dates and does not refer to the zodiac. In STT II 300 the passage parallel to those quoted above is (STT II 300 r12): “Sabatu 10th period of ‘A woman should not look [at a man]'”. As was the case with the Gestirn-Darstellung texts, the transmission from calendar dates to degrees of zodiacal signs is quite automatic. In the ideal calendar, the sun is in Aquarius 10° on the 10th day of the 11th month — not the moon.” (Koch-Westenholz, 1995, p. 170)

Length of Day

Earlier in this article, I cited some examples from the MUL.APIN which correlate dates in the schematic calendar with day lengths and the phases of the fixed stars. I also noted that this association between the calendar, day lengths, phases of the fixed stars, and equinoxes goes back to the Old Babylonian period.

The length of day and night is a function of the ecliptic-equator relationship. It is a defining feature of the tropical year. Therefore, the 360 day calendar became associated with the features of the tropical year from an early period.

Influence on Mathematical Astronomy

The day length schemes associated with the calendar also played a major role in some later developments in mathematical astronomy.

“The Late Babylonian procedure text TU11 testifies to many more astronomical quantities derived from the length of day or night. We see that the ideal year was utilized heavily in the early formation of numerical astronomical theory.”  (Brack-Bernsen, Steele ed., 2007, Loc. 2625)

Part IV: Babylonian Zodiac Mechanics

We’ve seen how the 12 month schematic calendar served as a type of proto-zodiac. It served to connect the phases of the fixed stars with features of the tropical year such as the solistices and variation in length of day. The calendar was associated with all facets of Babylonian astrology from omen lore to later mathematical development. The regularization of the zodiac, the use of 12 signs of 30 degrees, and the use of Aries as the starting sign of the zodiac are among the features inherited from the calendrical proto-zodiac.

Some major questions remain. Did the Babylonians have a sense of precession? Did they know a distinction between tropical and sidereal cycles? Additionally, how did Babylonian longitudes work in practice? Do we know the original reference stars?

Calendar Shift

Unlike the Greek, the Babylonians did not have a geometrical sense of the ecliptic, nor did they have a desire to start the zodiac with the equinox. As noted above, some schematic arrangements began with the solstice, but the calendar had placed equinoxes and solstices in the middle of months. First, the Vernal Equinox was placed in the middle of month XII, then later in the middle of month I. The reasons for the shift pertain to the way they wanted to conceive of their ideal calendar, not due to precession.  Precession actually shifts the equinox earlier relative to the stars, not later.

The schematic calendar was only 360 days. Being over 5 days short of the true year, it would itself require intercalation about every 6 years. Therefore, its figures were truly ideals, rather than annual constants. The simple fact that the Babylonian regular zodiac came about shows that the Babylonians thought it possible to correlate the stars and constellations with an idealized tropical calendar. This argues for a lack of knowledge of precession. If they had suspected a clear distinction between tropical and sidereal cycles then the early history of the zodiac would surely look different. The zodiac represents an attempt move the ideal calendar onto the Sun’s ecliptic path of the stars, a more stable basis of measure than the shifting count of days. 360 days became 360 degrees.

Equinox at 8 or 10 Aries

Two systems for computing planetary phenomena and zodiacal longitude arose in Babylonian astral science with the advent of the zodiac. Both were used until the end of the Babylonian astral period and beyond. In System A the Vernal Equinox is said to occur at 10º Aries while in System B it occurs at 8° Aries. Presumably, this difference in the placement of the equinox occurred due to use of a different reference star as a starting point, but we can’t be sure. Early Hellenistic sources (e.g. Geminos and Thrasyllus) noted an 8° Aries equinox suggesting it was the more widespread conception in the latter period.

“We do not know what chronological relation existed between these two norms and what caused the difference. We have no evidence from Babylonian sources about a recognition of precession and we have no reason to assume that the difference of zero points in System A and B had anything to do with it, knowingly or unknowingly.” (Neugebauer, 2012, p. 368-369)

Reference Star Issues

Today, we are used to thinking of the tropical and sidereal zodiacs as being distinguished by the reference point used. If a reference star is used then it is a sidereal zodiac, while if the point of the equinox is used then it is a tropical zodiac. As ancient ephemerides (from about 3rd century BCE on) were by and large sidereal, it may come as a surprise that it took some detective work to find any specific reference star(s) which were originally used.

Ephemerides were often generated from past ephemerides using period functions that were sidereal and synodic. These mathematical periods were based on observed repeated planetary phenomena relative to the stars (sidereal) and other planets (synodic).  While there were Normal Star texts expressing rough planetary position relative to stars near the ecliptic, positions in the zodiac were calculated rather than observed.

No Known Reference Star?

In Francesca Rochberg’s 2004 book, “The Heavenly Writing”, she expressed that the reference star is unknown.

“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)

However, Rochberg was apparently not aware of the latest scholarship in that area when she wrote that. Scholars have since discovered that a few reference stars were indeed used in the early period.

The Reference Stars

Three referential boundary stars have been noted in recent years. Boundary stars would’ve been the most important early references for the Babylonian zodiac. Additionally, some early zodiacal texts gave the positions of Normal Stars in the zodiac which allows other Normal Stars to be used as references as well. For instance, one could say that a given Normal Star was in the 2nd degree of Sagittarius, and thus we’d know that the Sagittarius started about 2 degrees earlier.

“It was assumed that the boundaries of the zodiacal signs either coincided with (in the case of the Southern Rein of the Chariot (ζ Tau), the Rear Twin star (β Gem), and the Rear Star of the Goat-fish (δ Cap), which were taken to mark the beginning of Gemini, Cancer, and
Aquarius respectively) or at known distances in front of or behind a Normal Star (Huber, 1958; Jones, 2004). This link between the beginning of zodiacal signs and the location of stars indicates that the Babylonian zodiac was sidereal and therefore slips relative to our tropical zodiac over time, a conclusion confirmed through analysis of comparisons of Babylonian zodiacal positions with modern computation (Huber, 1958; Steele and Gray, 2007; Britton, 2010). Two star catalogues are known which give the positions of the Normal Stars within the signs of the zodiac (Roughton, Steele and Walker, 2004).” (Steele, 2018, p. 99)

End of the Preceding Modern Constellations

Beta Geminorum, aka Pollux, is found to have indicated the starting border of Cancer. It was also found that Zeta Tauri (Tianguan) and Delta Capricorni (Deneb Algedi) also marked the start of Gemini and Aquarius respectively. Interestingly, all those stars are part of the modern constellations just preceding the corresponding one from which Babylonian signs were named. In other words, a star in at the end of the constellation Taurus marked the start of the Babylonian sign Gemini, while one at the end of Capricorn marked the start of the sign Aquarius.

Ayanamsha of the Babylonian Zodiac

The approximate modern tropical longitudes of the three stars noted are about 25 3′ Gemini for zeta Tauri, 23°28’30” for beta Gemini, and 23°49′ for delta Capricorn. As beta Gemini and delta Capricorn agree with each other pretty closely (within about 21′), and beta Gemini is a very bright star said to mark the start of Cancer, I’ll be focusing on that one. We will work toward establishing an ayanamsha for the Babylonian zodiac that is consistent with scholarly findings.

“The sidereal zodiac appears to have been fixed so that the longitude of the bright star β Gemini was 90°. Consequently, the equinoxes and solstices occurred at about 10° of their respective signs in 500 BC, an amount which decreases due to precession by 1.4° per century or to roughly 5° by 150 BC.” (Britton and Walker, Walker ed., 1997, p. 49-50)

When The Zodiacs Coincided

Given the current position of Pollux, the ayanamsha is 23°28’30” for the Babylonian zodiac.  At the rate of precession of a degree every 71.57 years, this would mean the zodiacs coincided about 1,680 years ago (23.475*71.57), i.e. about 339 CE. This would also mean that tropical and sidereal longitudes would have differed by about 2 degrees in Valens’s time. That is relatively consistent with the differences found by pulling up Valens’s chart in the tropical zodiac vs. the (sidereally-derived) positions he gave in his text. See my article where I do just that.

The equinox would have been at about 10° Aries in the 4th, rather than 5th century (not 500 BC as noted by Britton and Walker). Still, Babylonian equinox calculations at that time were not precise, being based on gnomon and water clock. I have noted some of the issues with that sort of equinox calculation in my article on the age of the tropical zodiac. An error of a couple of days would not have been unreasonable. It was Hipparchus (2nd century BCE) who found a means of precisely locating the equinox.


Rochberg’s insistence on the inability to pinpoint a reference star and the fact that she refers to both stars and the equinox at different times as norming points can leave one very confused. Due to precession, the equinox and the stars cannot both be used as norming points without one running into some issues. One or the other will accumulate error and cease to be the norming point.

Similarly, one may wonder why the position of the equinox was said to be at 8 or 10 Aries for the whole of the use of the Babylonian zodiac. The Babylonians initially calculated the equinox on the basis of gnomon and water clocks which is not truly accurate for reasons discussed in that article. However, in the later period, rather than finding the equinox, it was calculated. For this reason, there doesn’t appear to have been any awareness that the equinox had shifted from its supposed position in the zodiac.

“The dates of solstices and equinoxes and of the heliacal rising of Sirius are recorded, but analysis has shown that at least during the Seleucid period (311 BC onwards) these are calculated, not observed.” (Britton and Walker, Walker ed., 1997, p. 50)

Ephemerides and Related Texts

Babylonian zodiacal positions were in time calculated rather than observed. The Babylonians did not have a clear geometric concept of the ecliptic, nor a geometric theory of planetary motion (unlike the Greeks). Babylonian ephemerides consisted of mathematical procedures for finding positions and timing other phenomena based on assemblages of functions which scholars term the “theory” for each planetary body.

“The theories are expressed in three classes of texts: ephemerides, which tabulate the functions necessary to compute the phenomenon in question for successive phenomena; procedure texts, which describe in compressed fashion the procedures for calculating each function; and auxiliary texts, which tabulate functions which relate to but do not figure directly in the computation of ephemerides.” (Britton and Walker, Walker ed., 1997, p. 49-50)


Babylonian planetary theory was not perfect. There was some degree of error and may have even been some slight zodiacal drift relative to the reference stars due to accumulated error.

“Kugler had already found that the Babylonian ephemerides were based on sidereal longitudes such that their “[Aries]0°” around -120 had a tropical longitude of about -4;36°. A very careful investigation of additional material by P. Huber showed that in about -100 the relation

λBab – λmod = 4;28±0;20°

holds. […] That the vernal point maintained in each of the two systems a fixed sidereal longitude indicates clearly that precession was unknown.” (Neugebauer, 2012, p. 369)

Accumulated Error

There are two things to note. First, difference of 4 1/2 degrees between the zodiacs in the year 100 BCE, would imply that the coincided near 220 CE (about 100 years earlier than what we found). The ayanamsha suggested by the ephemerides is also closer to 25°8′, about a degree and a half from that based on beta Gemini (Pollux) as 0 Cancer. Secondly, also note that there was about 20′ of variation on either side (total 40′ of variation among ephemerides). From these two facts we can surmise that the Babylonian zodiacal procedures were not precise. There was some zodiacal drift as well as some variation in Babylonian sidereal longitudes owing to error.


The tropical/sidereal distinction was not a clear one prior to the widespread knowledge of precession of the equinoxes. For the Babylonians, the stars and the ideal contours of the tropical year were correlated.

Why the Babylonians placed the equinox at 10 or 8 degrees of the Hired Man (Aries) is uncertain. Perhaps they had a specific reference star in mind. It is equally possible that they decided that they wanted the zodiac to have the equinox at 10 Aries and derived their reference stars based on their estimate for the location of the equinox. In either case, ephemerides were generated based on periods recorded with respect to bright stars near the ecliptic. In this way, longitudes remained relatively sidereally fixed while the assumed position of the equinox became increasingly erroneous.


Lunar phases, lunar proximity to stars and constellations, the solar cycle with its variations of day length and solar declination, and the phases of the fixed stars with respect to the Sun were all important means of measuring time and tracking omens.

The most sidereal elements pertained to the indication of location in the sky (particularly of the Moon) relative to certain ecliptic stars and to the constellations in the Path of the Moon.

The most tropical elements pertained to the division of the stars based on declination and the coordination of the phases of the stars with solar declination and variation in length of daylight through the idealized 360 day calendar.

The regularized 12 sign zodiac represents a synthesis of the “lunar” and sidereal constellations in the Path of the Moon with the “solar” and tropical 360 day calendar with 12 months of 30 days.

Hellenistic Astrology

Hellenistic astrology was not a continuation of the Babylonian tradition of astrology. It also was not a simple continuation of the tropical tradition of the Greek astronomers. Hellenistic astrology was a novel synthesis of elements from Babylonian, Egyptian, and Greek traditions while adding a number of new concepts.

The regularized zodiac is one of the key features of the system which owes a considerable debt to Late Babylonian astrology. The Hellenistic zodiac was not exactly the Babylonian one but fused some elements of the Babylonian with the Greek.

The zodiac in early Hellenistic astrology had both tropical and sidereal associations due to a lack of widespread knowledge of precession. The most common ephemerides were sidereally fixed. Evidently, astrologers thought they were tropically fixed as well.


My opinion is that the 12 sign regular zodiac was inspired by the regularity and symmetry of the tropical year. I believe the Greek astronomers had symmetry foremost in mind. They immediately set about setting the 0 point of the zodiac to coincide with the equinox. Therefore, I’m of the opinion that the tropical zodiac is of the calendrical spirit of the Babylonian zodiac. I also find the symmetries of the Greek version of that zodiac (starting at the equinox) to most logically and elegantly capture the Sun-Earth relationship. The ecliptic is what is being measured and its shape is defined by that Sun-Earth relationship.

Still, the zodiac clearly had both sidereal and tropical motivations and associations. Therefore, the choice of zodiac must ultimately come down to practical effectiveness rather than appeal to history. As astrology is a symbolic language of divination, there is room enough for two zodiacs used in somewhat different ways. I have found the tropical zodiac to be effective in my astrological work which is heavily informed by Hellenistic astrology. Yet, I’ve also had readings by Jyotish practitioners using the sidereal zodiac which were extremely insightful.

Signs and Stars

While overall I feel that the 12 sign regularized zodiac is suited for tropical orientation, I also see strong potential for the direct use of stars and constellations. Similarly, the sidereal zodiac can be used as a short-hand for positioning relative to stars and constellations. However, what I feel is often lacking today in astrology is that aspect of the zodiac which I called “lunar”, pertaining to observed phenomena relative to the stars themselves. Constellational zodiacs fit that bill.

Evidence for the use of constellations together with the regular zodiac abounds in Hellenisticl texts. For some examples, see “Greek Horoscopes” by Neugebauer and Van Hoesen. Many example charts show the use of constellations (namely parans) as indicating additional important information. For instance, in one katarchic example (p. 145), the constellation Ophiucus is used. The fact that Ophiucus (Asclepius/Hygeia) rose with the Moon is used as an indication of the involvement of medicine. I see in such examples potentially untapped symbolism within the Hellenistic system. I’d like to see renewed astrological interest in the constellations and their associations.

Further Reading

Over the last year or so, I have written a number of articles on the zodiac. For those interested in some of the puzzling issues that come up in early Hellenistic texts, I recommend reading the article on planetary days. In that article, I explored the birth chart of Vettius Valens, as well as why he is suspected to have used sidereal ephemerides. Additionally, in an article on length of life techniques, I touched on the use of symmetrical rising times in Manilius and Valens.

In terms of zodiacal history, I recommend reading the article on the early Greek use of the tropical zodiac. In that article, I trace how an explicit and conscious tropical orientation for the zodiac is linked with the master Greek astronomers and their geometric emphasis.

When it comes to choosing a zodiac for Hellenistic astrological work, I provided my own rationale for using the tropical zodiac for such work. That article is called Why Use the Tropical Zodiac? and uses a number of chart examples. Additionally, I touched on how some of the sign qualities correlate with the tropical cycle in the lesson on the signs of the zodiac.

Scholarly Resources

Those looking to dig a little deeper into the scholarly resources can find some great places to start in the References to this article. A great short recent article to start with is John Steele’s 2018 “THE DEVELOPMENT OF THE BABYLONIAN ZODIAC: SOME PRELIMINARY OBSERVATIONS“. The PDF of that article is available for free in full online (follow linked title). That and the other academic references here provide additional references of their own which are worthy of your attention.


De Jong, T. (2007). Astronomical dating of the rising star list in MUL.APIN. Wiener Zeitschrift Für Die Kunde Des Morgenlandes,97, 107-120. Retrieved from

Diamond, J. M. (1997). Guns, Germs and Steel: The Fates of Human Societies.

Hesiod, & Evelyn-White, H. G. (1914). Hesiod, the Homeric Hymns, and Homerica. Retrieved from

Hunger, H., & Steele, J. (2018). The Babylonian Astronomical Compendium MUL.APIN.

Koch, U. S., & Institut, C. N. (1995). Mesopotamian Astrology: An Introduction to Babylonian and Assyrian Celestial Divination. Retrieved from

Krupp, E. C. (1983). Echoes of the ancient skies: the astronomy of lost civilizations.

Lehoux, D. (2007). Astronomy, Weather, and Calendars in the Ancient World: Parapegmata and Related Texts in Classical and Near-Eastern Societies.

Neugebauer, O., & Van Hoesen, H. B. (1987). Greek Horoscopes. Retrieved from

Neugebauer, O. (2012). A History of Ancient Mathematical Astronomy. Springer Berlin Heidelberg. Retrieved from

Newton, I., Tonson, J., Conduitt, J., & Longman, T. (1728). The Chronology of Ancient Kingdoms Amended: To which is Prefix’d, A Short Chronicle from the First Memory of Things in Europe, to the Conquest of Persia by Alexander the Great. Retrieved from

Rochberg, F. (2004). The Heavenly Writing: Divination, Horoscopy, and Astronomy in Mesopotamian Culture.

Rhoades, J. (1891). The Georgics of Virgil. Retrieved from

Steele, J. M. (2007). Calendars and Years: Astronomy and Time in the Ancient Near East. Locations cited are from Kindle Edition.

Steele, J. (2018). THE DEVELOPMENT OF THE BABYLONIAN ZODIAC: SOME PRELIMINARY OBSERVATIONS. Mediterranean Archaeology and Archaeometry18(4), 97-105.

Walker, C. B. F. (1997). Astronomy Before the Telescope. St. Martin’s Press.

Image Attributions

Featured image by Prioryman [CC BY-SA 4.0], via Wikimedia Commons
Mesopotamia map image by Goran tek-en [CC BY-SA 4.0], via Wikimedia Commons

Rebus IBM image is in the public domain.

Map showing Babylonia and Assyria c. 1450 BCE is in the public domain.

Photo of artifact portraying Nisaba by Osama Shukir Muhammed Amin FRCP(Glasg) [CC BY-SA 4.0], via Wikimedia Commons

Image of Celestial Sphere by Tfr000 (talk) 15:34, 15 June 2012 (UTC) [CC BY-SA 3.0], via Wikimedia Commons



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

5 thoughts on “The Origin of the Zodiac

  • November 11, 2019 at 12:00 am

    Tropical is based on a hemisphere-sun relationship, not Earth-sun. The apparent relationship.

    • November 11, 2019 at 10:08 am

      Yes, an actual Earth-Sun relationship. It is the mathematical intersection of two planes defined by actual measurable astronomical motions. The ecliptic which is defined by motion of the Sun relative to the Earth or Earth relative to the Sun (motion is always relative), and the celestial equator which is defined by the Earth’s rotation (the plane perpendicular to the Earth’s axix of rotation) and is what defines the “hemispheres”.

  • July 13, 2019 at 7:42 am

    Hola Juan. Gracias. Estos son comentarios profundos. Una astrologia era en la India pero sin las casas, los signos, y otras cosas, hasta el primero o secundo siglo de la era comun. Las casas y algunas otras cosas se originan de la astrologia helenistica. La astrologia helenistica era una sistema de astrologia de los hablantes de griegos en la region, particularmente Egipto del 200-100 BCE. Algunos de mis otras articulos pertenecen a estos temas pero no todos ellos. Disculpa mi pobre espanol. Cuidese, Ant

  • July 8, 2019 at 3:55 pm

    Maravilloso artículo sobre el origen del zodíaco. Yo tengo algunas preguntas. Por ejemplo, cómo se asignaron as regencias planetarias para lo signos. Y la otra, cómo se originó la astrología en la India. Mil gracias


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