<p>The constellations were devised in Greece. They grouped the stars in ways that told stories. They put a structure onto the sky. There was never any attempt to divide the sky into equal sized parts. Some of the constellations were just bigger than others.</p>

<p>The stars are not logically or evenly laid out, and the stories that are told about the stars did not require even sized constellations.</p>

<p>From ancient times to now the constellations have proved a convenient, if somewhat quirky, way of arranging the sky. Astronomers divided the sky into regions, each named after the constellation it contained although with some variation, for example splitting the claws of the scorpion off and creating "Libra". Astrologers split the year into 12 months based on the general position of the sun. The astrological periods don't match up very well with the actual borders of the constellations. For example, the sun is within the modern borders of Libra between Oct 31 and Nov 22. Whereas astrologers will say that the sun birth sign is from September 23 to October 22. </p>

CC BY-SA 4.0
2018-05-20T05:44:27.537Z
That's what really confuses me: the astrology signs are pretty "even" in their ranges, but the ones on the sky are varying much more? How does that make any sense?
coolmap
CC BY-SA 4.0
2018-05-20T06:59:59.547Z
Its astrology.  Why do you expect "sense".  It seems that the astrologers divided the year into 12 periods and named each one after a constellation, so when an astrologer says "mercury is in Libra", it actually isn't. Don't ask me why.
James K
CC BY-SA 4.0
2018-05-20T15:52:40.527Z
Please don't swear. If you have an astrology question, please ask it on a relevant forum.  Not here.
James K
CC BY-SA 4.0
2018-05-20T21:45:39.383Z
@coolmap The reason nobody wants to explain astrology to you is because it is unexplainable. It is not based on actual math and is completely made up. For example, the Sun actually passes through 13 zodiacal constellations (most astrologers leave out Ophiuchus even though the Sun is in that constellation longer than it is Scorpio). Astrologers also don't account for the precession of the equinox. If you're looking for sense in astrology, you're gonna be looking for a long time, and insulting people here won't help you find it either.
zephyr
CC BY-SA 4.0
2018-05-20T22:00:13.677Z
Those "houses" are unrelated to the constellations, though... You may be right about Astrology making up things, but you don't seem like an expert on the subject. (Or I have got this wrong, but it doesn't seem like it when I study charts.)
coolmap
CC BY-SA 4.0
2018-05-20T23:41:10.093Z
OP has a point. [House](https://en.wikipedia.org/wiki/House_%28astrology%29) appears more closely related to sidereal time than to ecliptic longitude.
Mike G
CC BY-SA 4.0
2018-05-23T10:15:01.620Z
I have no problem with a scientific critique of astrology's claims to be able to describe personality or predict events, but comments like "[astrology] is not based on actual math and is completely made up", or confusing astrology's *signs* (the ecliptic divided into 12 equal segments) with *houses* (sidereal day divided into non-equal segments), or Mayans predicting the Age of Aquarius, are painfully ignorant. There's no excuse for uninformed denunciations. @JamesK's comment is the preferable approach: **factual** dismissal.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2018-05-19T23:11:52.717Z
2018-05-19T23:11:52.717Z
James K
<p>The constellations are artifacts of visual pattern recognition, many dating back to antiquity.
As the stars are distributed unevenly, naturally some constellations are larger than others.
Ptolemy catalogued 48 of them around 150 CE.
The other 40 were added between 1596 and 1763, either to cover the far southern sky or to fill gaps between the older figures.
Ian Ridpath gives a comprehensive history in <a href="http://www.ianridpath.com/startales/contents.htm" rel="noreferrer">Star Tales</a>.</p>

<p>The modern constellation boundaries were <a href="http://www.ianridpath.com/boundaries.htm" rel="noreferrer">standardized in the 1920s</a> by an IAU committee led by Eugène Delporte.
Their goals were to assign each square degree of sky unambiguously to one constellation, to be consistent with scientific literature already published, and to preserve the traditional figures where possible.
Equal size wasn't on the agenda.
The boundaries align with the <a href="https://en.wikipedia.org/wiki/Equatorial_coordinate_system" rel="noreferrer">equatorial grid</a> as of 1875:</p>

<p><a href="https://i.sstatic.net/mBfnG.png" rel="noreferrer"><img src="https://i.sstatic.net/mBfnG.png" alt="IAU constellation boundaries"></a></p>

<p>The zodiac of 12 equal parts was invented by the <a href="https://en.wikipedia.org/wiki/Zodiac#Early_history" rel="noreferrer">Babylonians around 400 BCE</a> and later refined by Ptolemy.
Each sign corresponds to a box 30 degrees wide and about 20 degrees high.
It's important to distinguish between a constellation (a visual group of bright stars) and a sign (a uniform box along the ecliptic).
For example, Virgo the <em>sign</em> spans <a href="https://en.wikipedia.org/wiki/Ecliptic_coordinate_system" rel="noreferrer">ecliptic longitudes</a> 150$^\circ$ to 180$^\circ$, whereas Virgo the <em>constellation</em> is somewhat wider and farther east.
In Ptolemy's time the signs and constellations were not far apart:</p>

<p><a href="https://i.sstatic.net/0kXwo.png" rel="noreferrer"><img src="https://i.sstatic.net/0kXwo.png" alt="Zodiac in the time of Ptolemy"></a></p>

<p>Ptolemy defined the <a href="https://en.wikipedia.org/wiki/Sidereal_and_tropical_astrology" rel="noreferrer">tropical zodiac</a> in reference to the equinoxes and solstices; for example, the boundary between the signs of Gemini and Cancer lies at the June solstice, wherever that may be among the stars.
Consequently, <a href="https://en.wikipedia.org/wiki/Axial_precession" rel="noreferrer">precession</a> makes the signs drift westward about 1.4$^\circ$ per century relative to the constellations.
In the present day, the zodiac is roughly one sign ahead of its constellations:</p>

<p><a href="https://i.sstatic.net/dQp9i.png" rel="noreferrer"><img src="https://i.sstatic.net/dQp9i.png" alt="Zodiac in the present day"></a></p>

CC BY-SA 4.0
2018-05-23T04:32:43.317Z
Although the effort is appreciated, this just makes me even more confused, frankly...
coolmap
CC BY-SA 4.0
2018-05-27T21:03:55.533Z
@coolmap Revised, hopefully clearer.
Mike G
CC BY-SA 4.0
2018-05-31T23:35:01.137Z
Yes, it became clearer now, especially with the images. Thanks a lot. And I'm happy that I now know that it's not wrong to say that I'm a Leo, even though when looking at the *constellations* for my birth moment in Stellarium, the sun has gone into Cancer, because the "sign" data has not changed over the years and only shares the names of the "zodiacs". Confusing stuff.
coolmap
CC BY-SA 4.0
2018-05-22T19:59:56.113Z
2018-05-28T13:45:11.247Z
2018-05-28T13:45:11.247Z
Mike G
<p>Can somebody tell me why the constellations I've marked here have areas that resemble pieces of a puzzle, with very varying width and height and shapes, instead of being logically/evenly laid out on the sky?</p>

<p>Virgo is much bigger than Cancer, for example.</p>

<p>The image is a screenshot from Stellarium.</p>

<p><a href="https://i.sstatic.net/6zgo2.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6zgo2.jpg" alt="enter image description here"></a></p>

CC BY-SA 4.0
2018-05-19T20:07:00.703Z
Humans made up the constellations and humans are *not* known for being particular good at logic, in my experience.
StephenG - Help Ukraine
CC BY-SA 4.0
2018-05-19T20:24:57.943Z
Well, they don't seem to match up to the much more "evenly spaced" astrological time spans, which are basically 1 month each? How does that make any sense?
coolmap
CC BY-SA 4.0
2018-05-21T15:38:23.597Z
I'm voting to close this question as off-topic because this is about Astrology, not Astronomy
Carl Witthoft
CC BY-SA 4.0
2018-05-21T16:13:43.333Z
@StephenG It is true, but why they had such illogical decision, may have already a logical answer.
peterh
CC BY-SA 4.0
2018-05-21T16:14:53.797Z
@CarlWitthoft I can't see astrology here (what should be purged out if appears), but I think it is more like about science history which is ontopic both here and on the HSM.
peterh
<constellations>
Why oddly shaped constellation areas?
coolmap
# Why oddly shaped constellation areas?

(Asked by: username_0 on 2018-05-19)

Can somebody tell me why the constellations I've marked here have areas that resemble pieces of a puzzle, with very varying width and height and shapes, instead of being logically/evenly laid out on the sky?

Virgo is much bigger than Cancer, for example.

The image is a screenshot from Stellarium.

[![enter image description here](https://i.sstatic.net/6zgo2.jpg)](https://i.sstatic.net/6zgo2.jpg)

**Tags:** constellations

> **Comments:**
> **username_1**: Humans made up the constellations and humans are *not* known for being particular good at logic, in my experience.  
> **username_0**: Well, they don't seem to match up to the much more "evenly spaced" astrological time spans, which are basically 1 month each? How does that make any sense?  
> **username_2**: I'm voting to close this question as off-topic because this is about Astrology, not Astronomy  
> **username_3**: @username_1 It is true, but why they had such illogical decision, may have already a logical answer.  
> **username_3**: @username_2 I can't see astrology here (what should be purged out if appears), but I think it is more like about science history which is ontopic both here and on the HSM.  

---

## 2 answers

### Answer by username_6 on 2018-05-22. Score: 8 | Accepted answer

The constellations are artifacts of visual pattern recognition, many dating back to antiquity.
As the stars are distributed unevenly, naturally some constellations are larger than others.
Ptolemy catalogued 48 of them around 150 CE.
The other 40 were added between 1596 and 1763, either to cover the far southern sky or to fill gaps between the older figures.
Ian Ridpath gives a comprehensive history in [Star Tales](http://www.ianridpath.com/startales/contents.htm).

The modern constellation boundaries were [standardized in the 1920s](http://www.ianridpath.com/boundaries.htm) by an IAU committee led by Eugène Delporte.
Their goals were to assign each square degree of sky unambiguously to one constellation, to be consistent with scientific literature already published, and to preserve the traditional figures where possible.
Equal size wasn't on the agenda.
The boundaries align with the [equatorial grid](https://en.wikipedia.org/wiki/Equatorial_coordinate_system) as of 1875:

[![IAU constellation boundaries](https://i.sstatic.net/mBfnG.png)](https://i.sstatic.net/mBfnG.png)

The zodiac of 12 equal parts was invented by the [Babylonians around 400 BCE](https://en.wikipedia.org/wiki/Zodiac#Early_history) and later refined by Ptolemy.
Each sign corresponds to a box 30 degrees wide and about 20 degrees high.
It's important to distinguish between a constellation (a visual group of bright stars) and a sign (a uniform box along the ecliptic).
For example, Virgo the *sign* spans [ecliptic longitudes](https://en.wikipedia.org/wiki/Ecliptic_coordinate_system) 150$^\circ$ to 180$^\circ$, whereas Virgo the *constellation* is somewhat wider and farther east.
In Ptolemy's time the signs and constellations were not far apart:

[![Zodiac in the time of Ptolemy](https://i.sstatic.net/0kXwo.png)](https://i.sstatic.net/0kXwo.png)

Ptolemy defined the [tropical zodiac](https://en.wikipedia.org/wiki/Sidereal_and_tropical_astrology) in reference to the equinoxes and solstices; for example, the boundary between the signs of Gemini and Cancer lies at the June solstice, wherever that may be among the stars.
Consequently, [precession](https://en.wikipedia.org/wiki/Axial_precession) makes the signs drift westward about 1.4$^\circ$ per century relative to the constellations.
In the present day, the zodiac is roughly one sign ahead of its constellations:

[![Zodiac in the present day](https://i.sstatic.net/dQp9i.png)](https://i.sstatic.net/dQp9i.png)

> **Comments:**
> **username_0**: Although the effort is appreciated, this just makes me even more confused, frankly...  
> **username_6**: @username_0 Revised, hopefully clearer.  
> **username_0**: Yes, it became clearer now, especially with the images. Thanks a lot. And I'm happy that I now know that it's not wrong to say that I'm a Leo, even though when looking at the *constellations* for my birth moment in Stellarium, the sun has gone into Cancer, because the "sign" data has not changed over the years and only shares the names of the "zodiacs". Confusing stuff.  

---

### Answer by username_4 on 2018-05-19. Score: 3

The constellations were devised in Greece. They grouped the stars in ways that told stories. They put a structure onto the sky. There was never any attempt to divide the sky into equal sized parts. Some of the constellations were just bigger than others.

The stars are not logically or evenly laid out, and the stories that are told about the stars did not require even sized constellations.

From ancient times to now the constellations have proved a convenient, if somewhat quirky, way of arranging the sky. Astronomers divided the sky into regions, each named after the constellation it contained although with some variation, for example splitting the claws of the scorpion off and creating "Libra". Astrologers split the year into 12 months based on the general position of the sun. The astrological periods don't match up very well with the actual borders of the constellations. For example, the sun is within the modern borders of Libra between Oct 31 and Nov 22. Whereas astrologers will say that the sun birth sign is from September 23 to October 22.

> **Comments:**
> **username_0**: That's what really confuses me: the astrology signs are pretty "even" in their ranges, but the ones on the sky are varying much more? How does that make any sense?  
> **username_4**: Its astrology.  Why do you expect "sense".  It seems that the astrologers divided the year into 12 periods and named each one after a constellation, so when an astrologer says "mercury is in Libra", it actually isn't. Don't ask me why.  
> **username_4**: Please don't swear. If you have an astrology question, please ask it on a relevant forum.  Not here.  
> **username_5**: @username_0 The reason nobody wants to explain astrology to you is because it is unexplainable. It is not based on actual math and is completely made up. For example, the Sun actually passes through 13 zodiacal constellations (most astrologers leave out Ophiuchus even though the Sun is in that constellation longer than it is Scorpio). Astrologers also don't account for the precession of the equinox. If you're looking for sense in astrology, you're gonna be looking for a long time, and insulting people here won't help you find it either.  
> **username_0**: Those "houses" are unrelated to the constellations, though... You may be right about Astrology making up things, but you don't seem like an expert on the subject. (Or I have got this wrong, but it doesn't seem like it when I study charts.)  
> **username_6**: OP has a point. [House](https://en.wikipedia.org/wiki/House_%28astrology%29) appears more closely related to sidereal time than to ecliptic longitude.  
> **username_7**: I have no problem with a scientific critique of astrology's claims to be able to describe personality or predict events, but comments like "[astrology] is not based on actual math and is completely made up", or confusing astrology's *signs* (the ecliptic divided into 12 equal segments) with *houses* (sidereal day divided into non-equal segments), or Mayans predicting the Age of Aquarius, are painfully ignorant. There's no excuse for uninformed denunciations. @username_4's comment is the preferable approach: **factual** dismissal.  

---

