The Tropical, Sidereal and Constellational Zodiacs
Over the past few weeks there has been a lot of discussion about the zodiac in the mainstream media. Unfortunately most of it has been misinformation and false reports, deliberately designed to make people question the validity of astrology.
In order to set the record straight, I’m writing a two part series of articles on the zodiac and the recent zodiac controversy.
In this article I will focus on what the zodiac is as a reference system, and what the difference is between the zodiacs in the east and west.
This will be followed up by a separate article which documents the recent zodiac controversy and answers some questions about it from an astrologer’s perspective.
The Constellational Zodiac
Ancient astronomers noticed that the Sun, Moon and five visible planets regularly wander through a very specific path in the sky. Because the planets never deviate from this path, which we call the ecliptic, there are certain constellations on that path that the planets repeatedly walk through.
This is how the constellational zodiac was first developed. It included every constellation that the planets actually moved through, and it excluded constellations that they didn’t move through.
This is what that looks like if you were to observe the planets moving through the zodiacal constellations over the course of a year:
Notice that the constellations are of unequal size. Some are kind of small, such as Cancer, while others are really large, such as Virgo. Some of them even overlap a little bit.
The Sidereal Zodiac
Eventually by the 5th century BCE astrologers/astronomers in Mesopotamia standardized the zodiac so that it contained 12 signs of exactly 30 degrees each. This is what is referred to as the sidereal zodiac.
Its reference point is the constellations, although the constellations themselves vary in size, some of them being relatively small and some being relatively large. So, the sidereal zodiac is sort of an idealized or symbolic division of the constellations into 12 equal segments or “signs.”
The Tropical Zodiac
The system of astrology that most western astrologers use came together a few centuries later, around the 1st century BCE. Most of the things that we associate with astrology, including many of the characteristics of the signs of the zodiac, originated during this time.
Around this time the seasons were roughly aligned with the sidereal zodiac, so that the beginning of the seasons coincided with the beginning of the cardinal signs — Aries, Cancer, Libra and Capricorn. The middle of the seasons coincided with the fixed signs — Taurus, Leo, Scorpio and Aquarius. The end of the seasons coincided with the mutable signs — Gemini, Virgo, Sagittarius, and Pisces.
This alignment of the seasons with the signs of the zodiac is important because astrologers made symbolic associations between the nature of the seasons and the nature or meaning underlying certain signs of the zodiac. So, it wasn’t just about the appearance of the constellations or the myths associated with them, but information was also derived from the specific part of the season associated with certain signs.
For example, the cardinal signs Aries, Cancer, Libra and Capricorn are thought to reflect the initiation of new activities and changes because they coincide with the beginnings of the seasons, just after the equinoxes and solstices, where there is a distinct change in the weather and the things that depend on it. On the other hand, the fixed signs Taurus, Leo, Scorpio and Aquarius are said to reflect the stabilization of existing activities and circumstances since they coincide with the middle of the seasons, when there is a sense of stability in the heat and temperature. The mutable signs Gemini, Virgo, Sagittarius and Pisces are thought to reflect circumstances in which things are in transition because they lie at the end of the seasons, when there is a transition from one season to the next.
So, there are symbolic associations being made between the nature of different parts of the seasons and certain types of actions, circumstances or qualities that share a formal similarity. This is the basis of what is referred to as the tropical zodiac, which is measured relative to the seasons, with its starting point at the vernal equinox.
This is what that looks like if you were to observe the planets moving through the tropical zodiac over the course of a year, starting from the vernal point and then moving through each of the twelve 30 degree signs:
The Three Zodiacs
This means that there are essentially three zodiacs, or three reference systems that are all referred to as “zodiacs” (which is somewhat unfortunate since this convention is the source of quite a bit of confusion):
- Constellational Zodiac: based on the uneven constellations that lie in the path of the Sun, Moon and planets (a.k.a. the ecliptic)
- Sidereal Zodiac: the idealized zodiac with 12 signs of 30 degrees each that is roughly aligned with the constellations
- Tropical Zodiac: the idealized zodiac with 12 signs of 30 degrees each that is aligned with the seasons
Precession and the Adoption of the Tropical Zodiac in the West
Around the time that the basic principles of western astrology were systematized, in the 1st century, the sidereal zodiac associated with the constellations and the tropical zodiac associated with the seasons were roughly aligned, and astrologers drew information from both the constellations and the seasons associated with certain signs in order to determine the characteristics of those signs.
However, by this time astrologers and astronomers had already become aware of the phenomenon known as “precession,” in which the signs of the sidereal and tropical zodiac slowly drift apart from one another, at a rate of about 1 degree every 72 years or so.
Because of this gradual drift between the tropical and sidereal zodiacs, there came a point when western astrologers had to make a decision about which reference system was the basis of what they were doing with the signs of the zodiac. What they ended up doing was choosing the tropical zodiac associated with the seasons as their primary reference point, and continuing to call the tropical “signs” by their old names, which were originally derived from the constellations.
This happened definitively in the 2nd century CE when the famous astrologer/astronomer Claudius Ptolemy defined the first degree of Aries as the vernal equinox, which coincides with the first day of spring in the northern hemisphere. Western astrologers have been deliberately following this reference system, the tropical zodiac, for the past 1,800 years or so.
As a result of this decision to use the tropical zodiac of the seasons rather than the sidereal zodiac of the constellations, the zodiac used by most western astrologers is no longer associated with the constellations or the fixed stars. As a result, the two zodiacs differ by roughly 24 degrees at this point, which is almost one full sign, although not quite. So, a planet at 24 Aries in the tropical zodiac would be somewhere around zero degrees Aries in the sidereal zodiac.
The following diagram roughly depicts the difference at this point:
- The inner wheel shows the tropical zodiac, which is aligned with the equinoxes and the solstices.
- The middle wheel shows the sidereal zodiac, which is roughly aligned with the constellations, being about 24 degrees off of the tropical zodiac at this point.
- The outer ring is a really rough sketch of the constellations that fall on the ecliptic, just to give you an idea of how they vary in size. (Astrodienst has an option in its extended chart selection to include the zodiacal constellations, and a more accurate depiction of the constellations as they are aligned with the sidereal zodiac would look something like this.)
Use of the Tropical Zodiac Within the Context of Arguments About Precession
Virtually all western astrologers use the tropical zodiac, including those writing Sun-sign columns ever since they first started being published in newspapers in the 1930s. Because it is aligned with the seasons, it always stays fixed, and doesn’t change. It is a stable reference system.
Since the tropical zodiac is based on the seasons rather than the constellations, changes in the sidereal zodiac and the fixed stars as a result of precession are irrelevant. Not only is precession not relevant within the context of the tropical zodiac, but the fact that portions of other constellations fall on the ecliptic, such as Ophiuchus’s foot, is also irrelevant as well.
If the reference system that western astrologers use is not based on the constellations and is unaffected by precession, then skeptical arguments which focus on those points are both baseless and deliberately misleading.
The Use of the Sidereal Zodiac by Indian Astrologers
Now, to be fair, there are astrologers who use the sidereal zodiac, which is roughly aligned with the constellations, and they do adjust their calculations for precession. There was a strong connection between early western astrology and Indian astrology around the 1st and 2nd centuries, but the Indians decided to use the sidereal zodiac of the constellations rather than the tropical zodiac of the seasons.
The reason for this is probably that they had an earlier indigenous form of astrology that was based around a 27 “sign” lunar zodiac called the nakshatras, and this was firmly anchored in the sidereal framework since each sign of this lunar zodiac was tied to a specific fixed star.
This prior focus on the fixed stars via their lunar zodiac made the sidereal zodiac more appealing because it lined up better than the seasons, and as a result the vast majority of astrologers in India today use a sidereal zodiac.
The Baselessness of Skeptical Attacks on Tropical Astrology
Sidereal Indian astrology is not usually the subject of skeptical attacks such as the ones in the past few weeks. Rather, what is usually attacked is tropical western astrology, especially Sun signs. The statements that were widely circulated recently were that:
- There was a recent shift which has caused everyone’s Sun sign to be one sign off.
- There is a new constellation which means that there should now be 13 signs.
As I’ve tried to show above, both of these assertions are false within the context of the tropical zodiac used in western astrology. Within that context, nothing has changed in the past 2,000 years: there are still 12 signs of the zodiac, and everyone still has the same Sun sign. Precession does not change the composition of the tropical zodiac, nor does the fact that a small part of the constellation Ophiuchus falls on the ecliptic.
Assertions to the contrary basically amount to a propaganda campaign on the part of skeptics with the goal of undermining the standing of astrology in society. Their general position is that astrology is false to begin with, and thus anything that serves to undermine the public acceptance of it is essentially fair game, regardless of how inaccurate or misleading the statements might be. The end justifies the means.
These sorts of propaganda campaigns are waged all the time, though, so why did this one become such a media sensation? In the next article I will review the sequence of events and propose one possible theory.