Four Pillars and Eight Characters: Time and Space Coordinate System
Ganzhi calendar: a symbol system derived from the astronomical calendar
The Four Pillars and Eight Characters is a time-space coordinate system used in ancient China to record the time of birth of an individual. Its core is the Ganzhi calendar:
| Year Pillar | Month Pillar | Day Pillar | Hour Pillar | |
| Heavenly Stems | 甲 | 乙 | Bing (🌟 Day Master) | 丁 |
| Earthly Branches | 子 (Zodiac Sign) | 丑 | 寅 | 卯 |
Each of the four pillars is composed of a heavenly stem and an earthly branch, forming a cycle of sixty Jiazi. The eight characters are the eight characters composed of the four pillars of heavenly stems and earthly branches.
Solar terms:Geographical response to the solar radiation cycle
The division of the month pillar in the Eight Characters corresponds to the 24 solar terms, which are essentially divided by the sun’s ecliptic longitude every 15 degrees. The solar terms mark the periodic changes in solar radiation energy, affecting the seasonal laws of the earth’s ecosystem.
The Space-Time Logic of the Four-Pillar Model
| Four Pillars | Classification basis |
|---|---|
| Year Pillar | Beginning of Spring (solar ecliptic longitude 315°) |
| Month Pillar | 12 solar terms (seasonal divisions) |
| Day Pillar | Day and night alternation (true solar day) |
| Hour Pillar | Local true solar time (see the table below for the time corresponding to the earthly branches) |
Heavenly Stems
Heavenly Stems：The five elements are divided into yin and yang, so there are ten heavenly stems.
| Ten Heavenly Stems | Yin Yang Five Elements | Symbolism |
| 甲 | Yang Wood | Yang Qi is stirring, everything is breaking out of its shell, like a new life beginning |
| 乙 | Yin Wood | All things are born, and the branches and leaves are soft and curved, representing growth and softness |
| 丙 | Yang Fire | Yang fire is as bright and hot as the sun, symbolizing brightness and warmth. |
| 丁 | Yin Fire | All things are sturdy and robust (丁壮), like a person in their prime — strong, mature and energetic |
| 戊 | Yang Earth | Yang soil is lush, like the earth carrying all things, implying prosperity and stability |
| 己 | Yin Earth | All things are suppressed, and Yin soil means convergence, representing introversion and precipitation. |
| 庚 | Yang Metal | Yang metal is austere, symbolizing the transformation and renewal of autumn, which means a turning point |
| 辛 | Yin Metal | Yin Metal is pungent (辛) — sharp yet fine-grained, it represents delicacy and tenacity |
| 壬 | Yang Water | Yang water breeds, like the water of rivers, embracing and flowing, containing new opportunities |
| 癸 | Yin Water | Yin water is hidden, it is the end of the old and the beginning of the new, it represents potential and hope |
Earthly Branches
| Twelve Earthly Branches | Yin Yang Five Elements | Sign of the Zodiac | Position | Time | Solar terms |
| 子 | Yang Water | mouse | north | 23:00~01:00 | Heavy Snow |
| 丑 | Yin Earth | ox | middle | 01:00~03:00 | Minor Cold |
| 寅 | Yang Wood | tiger | East | 03:00~05:00 | beginning of spring |
| 卯 | Yin Wood | rabbit | East | 05:00~07:00 | Waking of Insects |
| 辰 | Yang Earth | dragon | middle | 07:00~09:00 | Qingming |
| 巳 | Yin Fire | snake | South | 09:00~11:00 | beginning of summer |
| 午 | Yang Fire | horse | South | 11:00~13:00 | Grain in Ear |
| 未 | Yin Earth | sheep | middle | 13:00~15:00 | Lesser Heat |
| 申 | Yang Metal | monkey | West | 15:00~17:00 | beginning of autumn |
| 酉 | Yin Metal | chicken | West | 17:00~19:00 | White Dew |
| 戌 | Yang Earth | dog | middle | 19:00~21:00 | Cold Dew |
| 亥 | Yin Water | pig | north | 21:00~23:00 | beginning of winter |
Earthly Branches：The twelve Earthly Branches form a cycle of 12 years, which is derived from the idealized simulation of the orbit of Jupiter (Year Star).
The Earthly Branches can be divided into three categories:
| Classification | Position in Each Season | Twelve Earthly Branches | |||
| Four Growths (四生) | The first month of each quarter | 寅 | 申 | 巳 | 亥 |
| Four Cardinals (四正) | Mid-month every quarter | 子 | 午 | 卯 | 酉 |
| Four Storages (四库) | End of each quarter | 辰 | 戌 | 丑 | 未 |
Earthly Branches Hidden Stems
The Earthly Branches are the form of the Heavenly Stems on the earth. The earth carries all things. The Earthly Branches are more complex than the Heavenly Stems. Each Earthly Branch may contain the energy of multiple Heavenly Stems, which is called the Earthly Branches Hidden Stems.
According to the strength of their power, the hidden stems in the Earthly Branches can be divided into: Original Qi, Middle Qi, and Residual Qi.
| Earthly Branches | Original Qi | Middle Qi | Residual Qi |
| 子 | 癸 | ||
| 丑 | 己 | 癸 | 辛 |
| 寅 | 甲 | 丙 | 戊 |
| 卯 | 乙 | ||
| 辰 | 戊 | 乙 | 癸 |
| 巳 | 丙 | 戊 | 庚 |
| 午 | 丁 | 己 | |
| 未 | 己 | 丁 | 乙 |
| 申 | 庚 | 壬 | 戊 |
| 酉 | 辛 | ||
| 戌 | 戊 | 辛 | 丁 |
| 亥 | 壬 | 甲 |