Z is for Zodiac

I’ve always been interested in astrology. I used to be able to calculate birth charts by hand, before apps could do it. I am also familiar with numerology, read palms, and interpret tarot cards. I often did tarot readings at corporate off sites. They were wonderful for discussing team strategy; people open up and speak their minds. I was also peppered with questions about why a person who did finance and math for a living was so knowledgeable about occult practices.

They shouldn’t have been surprised. Ancient astrology was heavily dependent on math and scientific measurement. Historians often find it quaint that astrology and astronomy were taught together, but to ancient Sumerians and Egyptians, this was like statistical analysis, using data to make predictions. Where today we might apply theories of random walk, Keynesian economics, or monetary policy–given that we are a society fueled by capitalism–in 2500 BCE, the ancients generated predictions based on interpretations of the night sky. Across multiple societies, astrologers were key advisors to the king-emperor-leader, in the same way that Cabinet members function today. Will the harvest be bountiful? Will the attack on a rival neighbor be a success? Should we apply tariffs? What actions should we take to maintain celestial harmony?

The zodiac might be easily dismissed as simple superstition. Yet, for all our modern access to information and expertise, our predictions aren’t necessarily more accurate. Economists disagree, and economic results don’t always follow predictions. Political polls seem no more conclusive than a newspaper horoscope. Meanwhile, today’s horoscopes bear very little connection to the horoscopes generated three thousand years ago, which were mathematically calculated based on that day and that person, not simple platitudes.

The cultures of ancient Mesopotamia, Egypt, China, Greece, and others paid close attention to the night sky and acted accordingly. Their view also linked the activities of the constellations, along with the sun, moon, and planets, to the seasonal climate of their environment. Weather was everything, and weather came from the heavens, which meant it was affected by the stars. Just as ancient cultures defined their calendar, months, and seasons, they also organized the heavens into the zodiac.

Three questions I will consider in this post:

1. Where does the zodiac “come from” and why was it arranged into twelve?
2. How did key ancient cultures interpret and use the zodiac?
3. What do the similarities and differences in these interpretations suggest?

My horoscope for today, April 30, 2025, says “Work hard, then indulge in play…” So let’s get to work.

Fixed Constellations, Wandering Planets

Here’s a short primer on how astronomy and the zodiac intersect. When you look up at night, you see groups of stars, constellations, which move as the night progresses. These constellations also move to different parts of the night sky at different times of year. We know now that the earth is itself moving through the universe, turning on an axis as it circles the sun, but you have to imagine it’s 6000 BCE, or even the 160 CE of Ptolemy. Think of the sky as a globe surrounding us, where you can only see the upper half. If you take a lot of measurements–and ancient astronomers did–you can describe in detail that “bowl” of sky overhead. If the Babylonians only had WYSIWIG computer graphics, they could have explained this quite well.

That celestial bowl or half-sphere is divided into twelve parts, each of which is associated with a specific constellation. The Sun, during the day, is in one of those twelve constellations of the zodiac. If you are a Cancer, it means the Sun was in the constellation called Cancer during the month you were born. But the zodiac constellations were only one piece of the predictive mechanism. The cultures of the Mediterranean further divided the day into twelve parts, each of which was ruled by a house that reflected an area of life, such as relationships, finances, or health.

Moreover, astronomers knew there were the sun, moon, and five planets, each of which moved around in that celestial bowl. Predictions were based on the movements of those planets (+sun and moon), the houses, and the zodiac. Positions changed by time of day, day of the month, month of the year, year of the decade. Those predictions required precise knowledge of the movement of the planets and constellations, reflecting measurements taken over hundreds of years. A horoscope wasn’t a guess. It required knowing to the minute when someone was born, then determining the position of all the planets, the houses, and constellations and interpreting the confluence of all those factors.

You might still react that this is all mystical claptrap, but it was mathematically complex mystical claptrap. I’m not on a crusade to change anyone’s belief system, to advocate that this was better. Feel free to continue to interpret the world according to what some guy quotes from a famous book on a certain day of the week in a building with crosses or, perhaps, to apply the Dead Cat bounce model to your investment portfolio. An estimated half the population doesn’t “believe” in evolution, and a large percentage can’t do long division. Knowledge is relative.

The Celestial Beauty of the Babylonian Least Common Multiple

The twelve-house, twelve-constellation system familiar to us was laid out by Claudius Ptolemy in @150 CE in Alexandria. Ptolemy was best known for his Almagest, the comprehensive model of astronomy that Islamic and medieval astronomers were still using, centuries later. Ptolemy’s astrological treatise, Tetrabiblos, provided an integrated look at the astronomy, math, theology, and philosophy behind the prevailing astrological model for astrology. Ptolemy’s model, with its assigned Latin names (Virgo, Taurus…), is well known today, but it’s worth noting that it’s called the Western Hellenic model. Ptolemy’s sky was the one over the Mediterranean in 160 CE. That celestial bowl looks different in the southern hemisphere and at different times.

Ptolemy also didn’t invent the system. The Sumerians (and Babylonians) are credited with doing so. Back in letter “C” (for Calendar), I explained that the Sumerians organized their calendar and measurements around base 60, which we still see in time (minutes, seconds) and geometry (degrees in a circle). The Sumerians liked 60, one argument says, because it divided by practically everything: 1, 2, 3, 4, 5, 6, 10… As it happens, sixty is also divisible by 12 and 12 itself is divisible by 1, 2, 3, 4, and 6. They divided the day into 24 and the year into 12. Maybe the Sumerians divided the sky into twelve because it was a handy number? That seems to be the prevailing notion.

One of the particular ways that the Sumerians used their data was to predict celestial events, such as eclipses or comets. Yes, they wrote about Halley’s comet in cuneiform. Often, the predictions were about omens:

If in Nisannu (April) the normal sunrise (looks) sprinkled with blood: there will be battles in the country.

From “Omens in the Stars, a Brief History.”

If the omens were negative, the kings would be told to make certain offerings in a certain way. If Saturn and Mars were going to be aligned on January 23, 669 BCE, the king should specifically focus on prayers to Saturn. It’s worth asking, what did they do before the zodiac system? They interpreted sheep livers. This seems at least a little more scientific. They had the astronomy down cold. At a mausoleum complex in Nemrut, a carved lion with the stars for Leo grouped near the moon can be interpreted as the day July 14, 109 BCE, the day King Mithridiates was crowned.

Decans and the Tzolkin

Systems of twelve were not the only way to organize the sky. The Egyptians, whose culture dated back as far if not farther than the Mesopotamians, divided the sky into 36 constellations of decans. While each of the 36 can be aligned with a Western zodiac sign, they were not originally related. The rising of each of the 36 constellations meant the beginning of a new decanal “hour” (Greek hōra) of the night for the ancient Egyptians, helping them to mark the position of time as a kind of “star clock.” This set of 10×36 was a way of dividing the sky according to base ten, the number of fingers we have, and connecting it with the 360 days in a year.

While the Internet may tell you that you can look at a Mayan zodiac, the Mayans also did not build it around the number twelve, and their expertise in astronomy was used for interpretation in a different way. Parallel to Sumerians, Egyptians, and others, the Mayans created detailed tracking systems for stars and planets, albeit with different names. They used this knowledge to build two calendars–a sacred 260-day one, the Tzolkin, and the 365-day one for ordinary but important uses, such as harvest.

Rather than personifying constellations, the Mayans paid close attention to the planets. Venus was especially important, and they timed rituals, battles, and coronation ceremonies according to Venus’ appearance and disappearance. Temples and monuments were aligned with stars and planets, and key events like the solstices and equinoxes were observed. The Mayans had astrologers to interpret the heavens, but no Western-style zodiac.

The Handy Chinese System

The zodiac could thus be seen as one kind of system to divide the sky and superimpose personification of gods or influencing factors that could drive interpretation. The Chinese also have a system of twelve based on animals, often called the Chinese zodiac. Where does the Chinese system fit in this schematic?

As Michael Ferlus explains, the Chinese also built a time-keeping system around the number 60, using a decimal system and a duodecimal (twelve-based) system together. Chinese tradition attributes this sexagesimal cycle to Emperor Huangdi, a Yellow Emperor, who reigned in 2637 BCE. This cycle of sixty was used to date particular years on the Oracle Bones, and it combined ten and twelve together to do so.

Ferlus suggest that ten and twelve logically derive from counting systems, aligning the Ten Heavenly Stems with fingers and the Twelve Earthly Branches with pieces of non-thumb fingers. This seems a more logical explanation than magic emperor Huangdi gets a brainstorm. It was later in the Han dynasty where the twelve branches were assigned to specific animals, although Ferlus shows that linguistically the animals originated in Thailand or Vietnam and traveled northward.

Regardless of where the Rat-Ox-Dragon and so forth came from, the system of twelve is part of the Chinese tradition today, though it is not a division of twelve parts of the sky, rather twelve year cycles. Ancient Chinese astronomers also could predict eclipses and interpret positive and negative omens based on celestial events. However, they superimposed other Chinese ideas, such as yin-yang, Taosim, and Confucianism, along with interpretations based on the day and month to form predictions to the emperor. Different ways of interpreting data for prediction.

The Western Zodiac and Precession of the Equinoxes

We have seen several cultures return to 360 or 12 as part of an alignment, using days of the year, fingers, or the mathematical magic of 3×4. But there’s one last pretty good argument about where the twelve signs emerged. Astronomer Alexander Gurshtein argues that the Sumerian zodiac–the familiar Western zodiac to us–originated from an interpretation of the precession of the equinoxes.

I’ve talked about the precession before, but the basic idea is that because the earth slightly “wobbles” as it spins, the part pointing north changes where it points over a 26,000 year cycle. So the constellations move around in a celestial bowl every day, and they change positions throughout the year, AND their starting point changes every 2160 years. Since 0 CE, the time since Jesus was born, the sun has been rising in the March equinox somewhere in Pisces. It’s about to move into Aquarius, which is why our coming age is called the Age of Aquarius.

Gurshtein notes that recorded history happened during the time of Taurus, and much of ancient history during the time of Aries. But he also says that humans by 6000 BCE had domesticated crops and animals, were living in settlements where calendars emerged, and had a good handle on symbolic astronomy, even if they didn’t have a uniform writing system. He argues that any of these groups would have recognized four primary constellations in four positions, not automatically twelve. The key constellations would have been those where the sun rises on the solstices and the equinoxes. In 6000 BCE, the time of Gemini, those four constellations would have been Gemini, Virgo, Sagittarius, and Pisces.

Hence, that Gemini “quartet” were the true “original” divisions of the western celestial sky, according to Gurshtein. They aligned to the seasons, which aligned to the life-source for humans in 6000 BCE. After two thousand years went by, astronomers would have seen a new quartet of four and given those new “key” star groupings their names: Taurus, Leo, Scorpio, and Aquarius. Then, as another two millennium went by, the astronomers–by then, writing in cuneiform, calculating with base 60 easily–added four final constellations and stopped. By then, twelve seemed like an obvious choice, even though the group that started it all was connected to the seasons, which meant only four.

The story that the Babylonians invented a thing we still use was my original angle for this post, but that become increasingly complicated as I researched the Chinese, Mesoamerican, and Egyptian systems. Not everyone uses the Aries-Taurus-Gemini zodiac. Other arrangements might be possible, even if that wheel of twelve remains compelling. In the end, the divisions are just an organizing system to explain complex movements of stars and planetary bodies whose calculations were hard to understand, let alone capture with the naked eye, without a computer, without even writing.

Yet the alphabet is also an arbitrary system, organized over time by Greeks and influenced by Romans. I chose it to structure a series of posts about history, to cover as much as I could about what was important to ancient cultures, comprehensively but without repetition. The alphabet–the zodiac–the march of animals across the days or the heavens–any system might be as good as another. Our human time does not just move in cycles, though, but also runs in a single, from alpha to omega. Always with a beginning and an end. I always remember the advice the king gives to the White Rabbit:

“Begin at the beginning,” the King said gravely, “and go on till you come to the end: then stop.”

So I will.

Thanks for reading.