Study note: This article is adapted from course materials and is provided for traditional culture study and theoretical research. On this site, Qi Men Dun Jia is introduced only as a Chinese cultural and symbolic timing model. It does not constitute decision-making, professional, financial, medical, legal, or personal advice.

1. Evolution of Qi Men Dun Jia Ju Systems

The number of Qi Men Dun Jia ju has gone through a historical process of simplification.

Jiang Ziya's seventy-two ju

In the older model attributed to Jiang Ziya, each solar term contains fifteen days. These fifteen days are divided into three five-day units:

Upper Yuan, Middle Yuan, Lower Yuan

Since the year contains twenty-four solar terms, the total number of configurations is:

24 solar terms × 3 yuan = 72 ju

This produces a highly detailed time structure.

Zhang Liang's eighteen ju

Later practice found that among the seventy-two ju, every four ju produced a repeated pattern:

72 ÷ 4 = 18

Zhang Liang therefore simplified the system into eighteen ju. This is the structure commonly used in modern Qi Men Dun Jia:

• Nine Yang Dun ju;
• Nine Yin Dun ju.

Yang Dun and Yin Dun

The eighteen ju are divided by the movement of seasonal qi:

• Yang Dun contains nine ju. It begins from Winter Solstice and continues until Summer Solstice, not including Summer Solstice. During this half of the year, yang qi gradually rises.
• Yin Dun contains nine ju. It begins from Summer Solstice and continues until Winter Solstice, not including Winter Solstice. During this half of the year, yin qi gradually rises.

This division makes the solar terms the central foundation for determining whether a chart uses Yang Dun or Yin Dun.

2. What Are the Three Yuan?

Each solar term contains fifteen days. These fifteen days are divided into three five-day periods:

When determining a Qi Men ju, identifying which yuan a day belongs to is essential.

In a complete sixty Jia Zi cycle, there are:

• Four Upper Yuan periods;
• Four Middle Yuan periods;
• Four Lower Yuan periods.

The three-yuan structure connects the solar-term calendar with the sixty Jia Zi cycle and provides the practical bridge for choosing the correct ju.

3. The Sixty Jia Zi and Xun Emptiness

In the stem-branch calendar, Heavenly Stems and Earthly Branches are paired in sequence. The pairing follows the rule:

Yang pairs with Yang; Yin pairs with Yin

Together, the ten stems and twelve branches form sixty combinations, known as the Sixty Jia Zi or sexagenary cycle.

Definition of emptiness

There are ten Heavenly Stems but twelve Earthly Branches. In each ten-day xun, two Earthly Branches cannot be paired with a Heavenly Stem. These two unpaired branches are called emptiness or Six Jia xun emptiness.

In Qi Men interpretation, emptiness often suggests:

• A matter has not materialized;
• Information may be unreliable or incomplete;
• Effort may temporarily produce little result;
• The current state may be suspended, missing, or not yet grounded.

Emptiness should not be read mechanically as good or bad. Its meaning depends on the question and on which palace, stem, gate, star, or useful symbol is empty.

Six Jia xun emptiness table

Each xun begins with a Jia combination. That leading Jia combination is called the xun head.

Both days and hours have their own emptiness. In chart construction, the stems hidden under the Six Jia xun heads—Wu, Ji, Geng, Xin, Ren, and Gui—are called the Six Instruments.

4. Solar Terms and the Gregorian Calendar

Solar terms are the key time markers used to determine Yin-Yang Dun and ju number. They also correspond closely with the solar Gregorian calendar.

Idealized time model

In the idealized Qi Men calendar model, time is divided as follows:

Actual astronomical solar terms vary slightly from year to year. Their exact Gregorian date and hour may shift by several hours, but the general date ranges remain stable.

Spring solar terms

The spring sequence is remembered in Chinese as:

Spring begins; rain arrives; insects awaken; spring divides; clarity comes; grain rain follows.

Spring Equinox corresponds to the 90-degree position in the circular ecliptic model.

Summer solar terms

Summer Solstice corresponds to the 180-degree position. Yin Dun begins from this point.

Autumn solar terms

Autumn Equinox corresponds to the 270-degree position.

Winter solar terms

Winter Solstice corresponds to the 360-degree or 0-degree position. Yang Dun begins from this point.

5. Bagua and the Twenty-Four Solar Terms

Qi Men Dun Jia uses the Later Heaven Bagua system.

In the Nine Palace and Bagua layout, excluding the central Earth of long summer, each outer trigram palace corresponds to three solar terms. Eight outer palaces multiplied by three terms each gives the twenty-four solar terms.

The Later Heaven Bagua correspondences are:

This arrangement explains why the solar terms are not merely dates. They are directional, elemental, and seasonal positions within the Qi Men cosmological map.

6. Solar Terms and Determining the Qi Men Ju

Determining the Qi Men ju depends mainly on two pieces of information:

1. Which solar term the date belongs to;
2. Whether the date falls in the Upper, Middle, or Lower Yuan.

Once these are known, one can determine whether the chart uses Yang Dun or Yin Dun and which ju number applies.

Solar-term ju table

The following table converts the Nine Palace solar-term diagram into a practical lookup form.

Core logic of the ju sequence

The ju-number pattern follows several important rules.

1. The numbers are separated by six

Within the same solar term, Upper Yuan, Middle Yuan, and Lower Yuan are separated by six in number.

For example, at Winter Solstice:

Upper Yuan: Yang 1
Middle Yuan: Yang 7
Lower Yuan: Yang 4

The difference between 1 and 7 is six. The shift from 7 to 4 also reflects the six-army structure after cycling through the nine-number system.

The reason is that the Six Jia structure contains six armies, each with ten members.

2. The first solar term of each palace matches the palace number

Kan, Gen, Zhen, and Xun are the four Yang palaces. Beginning with Winter Solstice, the solar terms are grouped three at a time and assigned clockwise through these palaces.

For the first solar term of each palace, the Upper Yuan ju number matches the palace number:

• Winter Solstice belongs to Kan 1, so its Upper Yuan is Yang 1;
• Beginning of Spring belongs to Gen 8, so its Upper Yuan is Yang 8;
• Spring Equinox belongs to Zhen 3, so its Upper Yuan is Yang 3;
• Beginning of Summer belongs to Xun 4, so its Upper Yuan is Yang 4.

The Yin half follows the reverse-counting structure beginning at Summer Solstice.

3. Later solar terms in the same palace continue the sequence

Within the same palace, the following solar terms continue the sequence.

For example, in the Kan 1 palace:

Winter Solstice: Yang 1, Yang 7, Yang 4
Lesser Cold: Yang 2, Yang 8, Yang 5
Greater Cold: Yang 3, Yang 9, Yang 6

This explains the transition from the Winter Solstice pattern of 1-7-4 to the Lesser Cold pattern of 2-8-5.

7. Practical Method for Determining a Ju

In practical chart construction, the procedure is:

1. Identify the Gregorian date and time of the question or event.
2. Determine which solar term the date belongs to.
3. Determine whether the day falls in Upper Yuan, Middle Yuan, or Lower Yuan by referencing the sixty Jia Zi cycle.
4. Use the solar-term ju table to determine Yang Dun or Yin Dun.
5. Select the specific ju number.

For example, if a date falls after Winter Solstice and belongs to the Upper Yuan, the chart uses Yang 1. If it falls after Winter Solstice but belongs to the Middle Yuan, it uses Yang 7. If it falls in the Lower Yuan, it uses Yang 4.

The key point is that Qi Men ju selection is not arbitrary. It is anchored in solar terms, the Three Yuan, the sexagenary cycle, and the Yin-Yang movement of seasonal qi.

8. Summary

This lesson introduced solar terms, the Three Yuan, and Qi Men ju configuration:

1. The older seventy-two-ju model divides twenty-four solar terms into Upper, Middle, and Lower Yuan.
2. Zhang Liang simplified the seventy-two ju into the eighteen-ju system used in modern Qi Men Dun Jia.
3. Yang Dun begins at Winter Solstice and contains nine ju.
4. Yin Dun begins at Summer Solstice and contains nine ju.
5. Each solar term contains fifteen days, divided into Upper, Middle, and Lower Yuan.
6. The sixty Jia Zi cycle explains xun heads and emptiness.
7. Emptiness indicates temporary non-materialization, uncertainty, or lack of grounding.
8. The twenty-four solar terms correspond to the Later Heaven Bagua outer palaces.
9. Determining a ju requires knowing both the solar term and the yuan.
10. The ju sequence follows palace number, Three Yuan structure, and forward or reverse movement in Yang Dun and Yin Dun.

Once this structure is understood, Qi Men chart construction becomes much clearer. The chart is no longer a disconnected set of symbols; it becomes a calendar-based and cosmological model in which solar motion, seasonal qi, Bagua direction, and the sixty Jia Zi cycle work together.