<p>The division of the sky into 30-degree gores was Babylonian.  The naming of each gore by a particular constellation came later.  The Babylonian number system worked in multiples and factors of 60, so 12 divisions with 30 degrees in each was a neat arrangement.  The fact that the sun moved by about one division in the time it took the moon to make a complete circuit was merely a nice coincidence.  But it isn't exact and can't justify the division into 30-degree sections.</p>
<p>The naming of the sections by constellations came later. The list of 12 constellations is newer than the division of the sky. For example, the constellation of <em>the scales</em> didn't exist, and those stars were consider to be the claws of the scorpion.  And of course the sun travels through <em>the snake holder</em>. So the division is not based only on the constellations that the sun passes through</p>
<p>Babylonian astronomers chose particular stars that were at 30 degree intervals, and then measuring relative to these stars. So they might say &quot;Ahead of the rear twin (Pollox) by 10 degrees.&quot;  The constellations that contained these reference stars then became the 12 zodiac constellations (which is why the snake holder got left out) And since two stars came from the scorpion, later astronomers split it off from the rest of the scorpion.</p>
<p>This system gives a basic framework for describing the ecliptic longitude of a planet.  But it is unsuited to the accuracy required for modern astronomy. So modern astronomers use numbers for coordinates, fixing the coordinates to the position of the vernal equinox, and have dropped the constellations <em>as a coordinate system</em>.</p>

CC BY-SA 4.0
2021-12-25T08:03:28.080Z
2021-12-25T08:03:28.080Z
James K
<p>My friend and I are arguing whether it is because there are 12 months or there are 12 constellations along this path. It makes more sense to me that, since there are 12 months, they divided the path into 12 pieces since there are 12 months and named this pieces accordingly. Am I wrong?</p>
<p>Thanks in advance</p>

CC BY-SA 4.0
2021-12-24T10:43:45.573Z
The question is: who is "they"?
planetmaker
CC BY-SA 4.0
2021-12-24T11:07:56.823Z
Well, there are a little more than 12 Moon phase cycles per solar year. But the Babylonians decided that it was a good idea to use a system based on 60 for dividing time and angles because 60 has [lots of factors](https://en.wikipedia.org/wiki/Highly_composite_number).
PM 2Ring
CC BY-SA 4.0
2021-12-24T11:19:57.777Z
I’m voting to close this question because this is not about astronomy and more about astrology.
Nilay Ghosh
CC BY-SA 4.0
2021-12-24T12:17:47.960Z
@Nilay It's not just about astrology, though. Sure, modern astronomy no longer uses the Zodiac signs, but it was standard through to the end of the 18th century to specify ecliptic longitude using the signs. See https://en.wikipedia.org/wiki/Ecliptic_coordinate_system#Historical_use And there is still a remnants of that system: the first point of Aries. And of course, we still refer to the tropics of Cancer & Capricorn.
PM 2Ring
CC BY-SA 4.0
2021-12-24T13:33:42.507Z
I believe this is a very legitimate question on the history of astronomy and should not be closed. Depending on the take it can surely have very interesting answers.
planetmaker
CC BY-SA 4.0
2021-12-24T14:27:14.650Z
@ PM 2Ring. Maybe I should divide the question into2 parts. 1 Are. Number of zodiaq signs(12) due to number of months? 2. Are 12 months due to rougly 12 months(moon spinning) during a year?
eral
CC BY-SA 4.0
2021-12-24T17:40:17.917Z
I added my vote to close as this is nothing to do with astronomy, and in fact Google would give the answer instantly
Rory Alsop
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2021-12-24T22:37:52.943Z
@eral *Welcome to Astronomy SE!* Don't worry about the close votes or negativity, I think you can make some small adjustments and get this reopened. Sometimes readers will overreact to certain things, for example thinking if Astrology is mentioned than Astronomy can't be involved. They of course both share the constellations of the Zodiac and as planetmaker points out the Zodiac was actively used by early astronomers to help understand the motion of the planets. Perhaps if you can remove "Astrology" or make it less prominent, and replace "they" with "early Astronomers" it will help a lot!
uhoh
CC BY-SA 4.0
2021-12-24T22:39:33.800Z
@eral If you like I can make those edits for you. By the way there are already two votes to reopen, three more are needed. So I think a wording adjustment will help speed this along.
uhoh
CC BY-SA 4.0
2021-12-24T23:16:13.520Z
I don't have the reputation points to vote to reopen, but I agree it's a good question, similar to the non-closed https://astronomy.stackexchange.com/questions/19301/period-of-unique-horoscopes

As a note, if you're talking about astronomical constellations as defined by the IAU, the sun travels through 13 constellations and other planets travel through up to 22 constellations: https://astronomy.stackexchange.com/questions/13086/what-constellations-touch-the-9-degree-wide-zodiac
Barry Carter
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2021-12-25T02:52:12.960Z
From https://astronomy.meta.stackexchange.com/a/538/16685 "if the questions are motivated by astrological sources but concern only astronomical phenomena, then they are on topic".
PM 2Ring
CC BY-SA 4.0
2021-12-25T12:52:15.110Z
It is about astrology and not about astronomy
tuomas
CC BY-SA 4.0
2021-12-28T13:25:09.480Z
@tuomas It's about astrology AND astronomy. The two are not mutually exclusive.
Barry Carter
<history><constellations><zodiac>
Why are there 12 zodiac signs?
eral
# Why are there 12 zodiac signs?

(Asked by: username_0 on 2021-12-24)

My friend and I are arguing whether it is because there are 12 months or there are 12 constellations along this path. It makes more sense to me that, since there are 12 months, they divided the path into 12 pieces since there are 12 months and named this pieces accordingly. Am I wrong?

Thanks in advance

**Tags:** history, constellations, zodiac
> **Comments:**
> **username_1**: The question is: who is "they"?  
> **username_2**: Well, there are a little more than 12 Moon phase cycles per solar year. But the Babylonians decided that it was a good idea to use a system based on 60 for dividing time and angles because 60 has [lots of factors](https://en.wikipedia.org/wiki/Highly_composite_number).  
> **username_3**: I’m voting to close this question because this is not about astronomy and more about astrology.  
> **username_2**: @Nilay It's not just about astrology, though. Sure, modern astronomy no longer uses the Zodiac signs, but it was standard through to the end of the 18th century to specify ecliptic longitude using the signs. See https://en.wikipedia.org/wiki/Ecliptic_coordinate_system#Historical_use And there is still a remnants of that system: the first point of Aries. And of course, we still refer to the tropics of Cancer & Capricorn.  
> **username_1**: I believe this is a very legitimate question on the history of astronomy and should not be closed. Depending on the take it can surely have very interesting answers.  
> **username_0**: @ PM 2Ring. Maybe I should divide the question into2 parts. 1 Are. Number of zodiaq signs(12) due to number of months? 2. Are 12 months due to rougly 12 months(moon spinning) during a year?  
> **username_4**: I added my vote to close as this is nothing to do with astronomy, and in fact Google would give the answer instantly  
> **username_5**: @eral *Welcome to Astronomy SE!* Don't worry about the close votes or negativity, I think you can make some small adjustments and get this reopened. Sometimes readers will overreact to certain things, for example thinking if Astrology is mentioned than Astronomy can't be involved. They of course both share the constellations of the Zodiac and as planetmaker points out the Zodiac was actively used by early astronomers to help understand the motion of the planets. Perhaps if you can remove "Astrology" or make it less prominent, and replace "they" with "early Astronomers" it will help a lot!  
> **username_5**: @eral If you like I can make those edits for you. By the way there are already two votes to reopen, three more are needed. So I think a wording adjustment will help speed this along.  
> **username_6**: I don't have the reputation points to vote to reopen, but I agree it's a good question, similar to the non-closed https://astronomy.stackexchange.com/questions/19301/period-of-unique-horoscopes  As a note, if you're talking about astronomical constellations as defined by the IAU, the sun travels through 13 constellations and other planets travel through up to 22 constellations: https://astronomy.stackexchange.com/questions/13086/what-constellations-touch-the-9-degree-wide-zodiac  
> **username_2**: From https://astronomy.meta.stackexchange.com/a/538/16685 "if the questions are motivated by astrological sources but concern only astronomical phenomena, then they are on topic".  
> **username_7**: It is about astrology and not about astronomy  
> **username_6**: @tuomas It's about astrology AND astronomy. The two are not mutually exclusive.  

---

## 1 answers

### Answer by username_8 on 2021-12-25. Score: 4 | Accepted answer

The division of the sky into 30-degree gores was Babylonian. The naming of each gore by a particular constellation came later. The Babylonian number system worked in multiples and factors of 60, so 12 divisions with 30 degrees in each was a neat arrangement. The fact that the sun moved by about one division in the time it took the moon to make a complete circuit was merely a nice coincidence. But it isn't exact and can't justify the division into 30-degree sections.

The naming of the sections by constellations came later. The list of 12 constellations is newer than the division of the sky. For example, the constellation of *the scales* didn't exist, and those stars were consider to be the claws of the scorpion. And of course the sun travels through *the snake holder*. So the division is not based only on the constellations that the sun passes through

Babylonian astronomers chose particular stars that were at 30 degree intervals, and then measuring relative to these stars. So they might say "Ahead of the rear twin (Pollox) by 10 degrees." The constellations that contained these reference stars then became the 12 zodiac constellations (which is why the snake holder got left out) And since two stars came from the scorpion, later astronomers split it off from the rest of the scorpion.

This system gives a basic framework for describing the ecliptic longitude of a planet. But it is unsuited to the accuracy required for modern astronomy. So modern astronomers use numbers for coordinates, fixing the coordinates to the position of the vernal equinox, and have dropped the constellations *as a coordinate system*.


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