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What Is The Zodiac And How Does It Work?

Oct 21st, 2022

Millions of light years away in the deep, dark reaches of space are billions of stars that, from our miniscule planet in our solar system, look like pictures, shapes and animals twinkling in the night sky. Though each of these stars are equally as far away from each other as we are from them, the groups and shapes that they make up have guided humans through rough seas and across vast deserts for millennia, and they have even given us the basis of our calendar year!

The constellations in the zodiac calendar have shaped much of early astronomy and astrology, and they still play an important part in culture today.

Here’s what the zodiac is, how it works and, of course, how it came about in the first place!

Zodiac constellations and their role in astrology

What is the zodiac?

The zodiac is a belt-shaped region of the sky along the path of the sun, a path often called the ecliptic. The planets in our solar system appear within this region as they also orbit the sun, and the moon generally sticks in this region as well. And, of course, there are plenty of stars from outside our own solar system that, for the most part, are contained entirely in this 16°-wide belt of the celestial sphere all year ‘round.

There are 12 major recognizable constellations within this belt, each taking up roughly 30° of this belt and separating it into 12 near-equal sections. These constellations make up the zodiac, each representing an animal or figure, and the location of these constellations in relation to the sun are used to mark the passage of time here on little old Earth. 

How does the zodiac work?

If the zodiac is a belt-shaped circle with the constellations evenly spaced on the inside, then the sun would be in the dead-center of this circle. The Earth would be orbiting the sun on an ellipsis, but definitely still in the middle of this belt.   

The zodiac calendar marks when the sun moves “through” a constellation on the zodiac. Of course, the sun doesn’t move through any of these, but to the ancient stargazers who saw the universe as a moving object and the Earth as a stationary one, the theory kind of makes sense. 


If we were to draw a line straight from Earth right through the sun and toward the belt beyond, the end of that line would point toward a constellation that, from Earth’s perspective, would be “containing” the sun at that time. As the Earth orbits the sun, that line would move and eventually point to a different constellation, and another, and another, so on and so forth, until that line would be right back to the same constellation a whole year and 360° later. 

Thus, the zodiac calendar separates our year into “star signs” that tell us what constellation the sun is passing through at that particular point in time. Twelve signs, 12 months — one year. Therefore your star sign is the one that was directly behind the sun in the month that you were born. 

History of the zodiac

Humans have been gazing at the heavens for as long as we’ve been around, so pinpointing the exact first time humans thought to assign stars to events is almost impossible. 

However, we do know that as far back as the 14th century B.C., ancient Egyptians had created a system that assigned 36 stars to the celestial plane, each one representing 10° of the 360° ecliptic. The decorative and highly elaborate tomb of Seti I in the Valley of the Kings is the oldest known representation of this system, dating back to at least 1279 B.C.

The Babylonians in the 10th–5th century B.C. took this idea and ran with it, creating their own system of classification and dividing the celestial plane into signs, rather than individual stars. People in this area also developed the first known celestial coordinate system around 409-398 B.C., back when they were under Persian rule. 

The Babylonians divided the ecliptic into 12 parts, each containing a constellation and taking up roughly 30° of celestial longitude. Each sign had 30 days assigned to it, resulting in roughly 1° of movement per day and 30 days of movement per sign. Thirty days per sign and 12 signs on the ecliptic meant around 360 days per entire cycle — giving us the basis of the modern calendar divided into 12 months. And 360 (ish) days.  

So cool!

Early records also show that ancient Babylonians referenced “The Great Twins” and “The Crayfish” in their celestial records, both of which are known today as Gemini and Cancer, respectively. 

This system was adopted by the Greeks around the 4th century B.C. and adopted in Ptolemaic Egypt, where the earliest depiction of the 12 zodiac signs can be found in the Hathor Temple at Dendera — a temple dedicated to the Egyptian god Osiris dated to around 50 B.C. There is also evidence suggesting that the zodiac system spread as far as India, as Hindu astrology presents echoes of the Greek zodiac in records from this time. 

The Middle Ages saw many Greek works translated into Arabic, generating a profound interest in the subject among Islamic scholars. Astrology became a discipline of its own and a great number of scholars and thinkers dedicated their lives to understanding the intricacies of the sun and its movement across the celestial plane. The most common area of study within astrology was Genethlialogy, the study of a person’s life in relation to the position of the sun and planets when they were born. 

In short, the early horoscope. 

Everyone from a commoner at a bazaar to a royal in a palace consulted astrology readers, including the Abbasid Caliph Al-Mansur whose reading convinced him to build the city of Baghdad. It was a valued part of society and would remain so for a long time, even after the zodiac was retired as a system of measuring the position of the sun in favor of the more-accurate equatorial coordinate system in the Renaissance. 

Though the zodiac is no longer used to measure the passage of stars, it’s still used as a basis for horoscopes in modern western astrology, which takes into account the position of the sun and planets on the day of a person’s birth. 

If you’re looking for a more in-depth history of the zodiac and astrology, here’s a cool documentary about the people, places and events that shaped our understanding of the zodiac today!

So, next time you’re wondering how the zodiac signs all fit together or why they are assigned to certain days, you’ll be following the footsteps of ancient stargazers who all were wondering the same thing. After all, humans have been looking to the stars for answers throughout our species existence, so why stop now?


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Featured photo courtesy Pixabay/MiraCosic

Author of Article

Colleen Ford is a South African who now lives in Spokane, Washington. She loves to travel, camp (in warm weather) and bake.

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