This was one of the big questions that I had when I started learning astrology. Why 12 zodiac signs, but not 11 or 13? There are information on the internet saying that there is a “new” zodiac sign, making it a total of 13 signs instead of 12, which was rather puzzling. And some took this to make a case that astrologers don’t really know what they are doing.
The Ecliptic – Path travelled by the Sun
Let’s start by asking ourselves this question – there are so many stars and constellations in the sky, with their various names. How did we arrive at this 12 signs (Aries, Taurus, Gemini etc)?
In the past, astrologers were also what we call “astronomers” today. They are one and the same person – observing what’s happening in the sky. I would think that the very first stellar body that they would start their observations with, would be the Sun. I think this is a reasonable guess given the importance of the Sun to our Earth and our daily habits.
I imagine that they would have noticed and marked down the directions where the Sun rise and set every day. And just before sunrise and just after sunset, when the stars are bright enough in the dark sky, they would also have used those directions to note down the constellations that the Sun is passing through.
This path that the Sun moves through in the sky is what we call the ecliptic today. And the star constellations that are on the path of the Sun? Indeed, they are the constellations of Aries, Taurus, Gemini…etc.
A division of time, not space
Back to our original question – why 12 zodiac signs? Why not any other number?
When I started my studies in astrology, like many others, I had understood the zodiac signs as the division of the sky into 12 portions, i.e. the zodiac signs serve as a division of space. This is the obvious interpretation that one can make.
Later on, my guru clarified that the zodiac signs are actually a division of time, not space, which to me was a mind-blowing change of perspective. To better appreciate this, we need to take a brief detour into how the ancients measured and tracked time.
Day, Month, Year
There are 3 time durations we can look at – day, month and year. To track time across a day, the Sun was used. We see evidence of this from the ancients that ranged from something as simple as a stick in the ground and measuring its shadows, to the more sophisticated sundials.
And what about a month? How did the ancients measure the duration of month? The key lies in the word itself, “month”. “Month” relates the Moon. The ancients used the lunar cycle of the Moon, which goes from full to dark then full again, to track the passage of time through a month. Therefore, a month is the period of time from one full moon to the next full moon. This system is still present today in calendars such as the Hindu calendar or the Chinese lunar calendar.
To track the passage of time through a year, the Sun’s cycle through the ecliptic was used. When the Sun returned to the same position along the ecliptic, using the star constellations as a guide, the ancients knew that a year has passed, and a new one has begun.
12 months in a year → 12 zodiac signs
And how does the 12 zodiac signs come into play? Well, a year is a long period of time, and the ancients needed a means to tell which part of the year they were in. One key application of this knowledge was agricultural planning, knowing when to start preparing for planting crops and when to harvest.
What the ancients did was to divide the year using the lunar cycle, since the Moon is easily observable. In a typical year, there are 12 full moons1. Hence the year is divided into 12, giving us 12 months. In order to know which month we are in, the Sun’s path through the stars (the ecliptic) also needs to be divided into 12, which gives rise to the 12 zodiac signs.
12 zodiac signs for the 12 months of a year – a division of time, not space.
Today, using the tropical zodiac, when we see that the Sun is entering the sign of Aries, we know that spring equinox is here, and the length of day will start to get longer than the length of night. Summer solstice coincides with the Sun entering the sign of Cancer, autumn equinox with the Sun entering Libra, and winter solstice with the Sun entering Capricorn. In this way, we know the time of year by knowing the tropical zodiac sign that the Sun is in.
I hope this has been useful! If you want to know more about astrology or get an astrology reading, head on over to this page.
Jerry Astrology 
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