The Twelve Signs — How the Tropical Zodiac Maps to the Earthly Branches

If you come from Western astrology, you already know the twelve signs of the zodiac — Aries, Taurus, Gemini, and so on. These twelve signs divide the ecliptic — the apparent path of the sun through the sky — into twelve equal segments of 30 degrees each, anchored to the vernal equinox.

What most Western astrologers don't realize is that classical Taoist astrology divides the same ecliptic into the same twelve equal segments. It just uses a different vocabulary — the Twelve Earthly Branches (地支), and specifically in the Monthly Commander (月将) ordering. Note that the Twelve Earthly Branches actually have two different ordering systems, and what we're presenting here is called the Monthly Commander. (Another ordering system is called the Monthly Constructor, which goes in reverse order.)

This is not a loose analogy. The Monthly Commander and the tropical zodiac signs are exactly the same division of the same sky, seen through different cultural lenses.

Each Branch corresponds to exactly one tropical sign. Each covers exactly 30 degrees of the ecliptic. The boundaries are defined by the same astronomical reference points — the solstices, equinoxes, and the midpoints between them.

In classical Chinese texts, sometimes the exact naming of Western signs would appear — and this is truly where beginners get tripped up! More specifically, when classical Chinese texts talk about Aries, Taurus, and so on, in most cases they actually meant the sidereal signs similar to Vedic astrology! This is where things get extremely confusing for modern Western readers.

However, I would argue that the cause of the confusion is because the Western astrological tradition chose to use the 12 zodiacal constellations — which inherently have meanings in observational astrology — to also denote the 12 tropical signs. In Taoist astrology, the 12 signs were derived from the solar-lunar calendar instead, and the signs change when the seasons change. Western astrology, by contrast, derived the 12 signs via observational astrology first, but then later adjusted for precession.

So Taoist astrology and Western astrology actually came to the same conclusion via different paths!

In addition, during later symbiosis with Vedic astrology, the Vedic/Western constellation names were imported into Chinese texts and were used to refer to sidereal signs — adding yet another layer of confusion for the modern reader.

To minimize confusion, this site will use the Twelve Earthly Branches (in the Monthly Commander ordering) interchangeably with the Western tropical signs. If you see the term "Aries," you should equate it to tropical Western Aries or the Earthly Branch 戌. We will not use "Aries" to mean sidereal Aries, unless explicitly specified. (This is not exactly how those terms are used in classical Chinese texts, but we believe this simplification will greatly help the Western reader.)

In later lessons, when we get to fixed stars and lunar mansions, we will use the Taoist constellation and mansion systems instead of Western constellations.

In Taoist astrology, the 12 Earthly Branches have two common orderings: the Monthly Commander and the Monthly Constructor.

The Monthly Commander (月将) essentially refers to the sun, and denotes that the sun commands the planets. The nature of the Monthly Commander is of solar essence — at the spring equinox, the corresponding Earthly Branch changes to 戌/Aries, and where the sun is at the spring equinox marks the beginning of 戌.

For those unfamiliar, the spring equinox (around March 20–21 each year) is the moment when the sun crosses the celestial equator heading northward, marking the beginning of spring in the northern hemisphere. It is the same anchor point that Western astrology uses to define the beginning of Aries — which is precisely why the two systems align.

We argue that this is a more elegant derivation of the tropical signs compared to Western astrology, which unnecessarily complicates things by starting with the observed location of the Aries constellation in ancient Greece and then applying a correction for precession.

Taoist astrology arrives at the same result directly through the calendar, without needing to reference constellations at all.

The other system for Earthly Branches, the Monthly Constructor (月建), uses the same Earthly Branches but in reverse order, because that is the order in which the handle of the Great Dipper rotates from season to season. While the sun commands, the Great Dipper translates that solar energy to earth and hence constructs. We will talk more about the Monthly Constructor in a later lesson, but for now we will use the Earthly Branches exclusively in the Monthly Commander ordering.