Yin Dun, Yang Dun & the Three Yuan Nine Ju

A Qi Men chart is not laid out at random. Before the Nine Stars, Eight Doors and Eight Deities take their palaces, the system must first decide two things: which palace to start from and which direction to count in. Those two things are the "Dun" (escape) and the "Ju" (chart number).

• Yang Dun (yang escape): used for the half-year after the Winter Solstice, when daylight is lengthening and yang qi is rising. The Six Instruments are distributed forward through the order of the Nine Palaces, while the Three Wonders are distributed in reverse.
• Yin Dun (yin escape): used for the half-year after the Summer Solstice, when yang qi is receding. The Six Instruments are instead distributed in reverse, while the Three Wonders go forward. Remember that it is not the whole chart running forward or backward as one: in Yang Dun the Six Instruments go forward and the Three Wonders reverse; in Yin Dun the Six Instruments go reverse and the Three Wonders forward.

The 煙波釣叟歌 (Song of the Misty Wave Angler) covers this in two separate places: "陰陽二遁分順逆，一氣三元人莫測" — the two escapes divide into forward and reverse, and the three Yuan within one solar-qi are hard to fathom — which speaks of the Dun and the Three Yuan; and "次將八卦論八節，一氣統三為正宗" — then take the Eight Trigrams to discuss the eight seasonal nodes; one solar-qi governing three periods is the orthodox method — which speaks of how a solar term governs its three Yuan.

That second line is about the Three Yuan. Each of the 24 solar terms lasts roughly fifteen days and is cut into three five-day periods called the Upper Yuan, Middle Yuan and Lower Yuan. Each Yuan is matched with its own starting number; since the Nine Palaces give nine numbers, these are the Nine Ju. With nine Ju for each of the two Dun, there are eighteen in total (the earth-plate chart settings); the whole chart still changes with the hour pillar and so on.

Look at the header line at the very top of the chart, not inside the palaces. It is usually written as:

Yang Dun Ju 3 · Upper Yuan · Chief Deity on the Heavenly Pillar Star · Chief Envoy on the Fright Door

It tells you three things:

1. Dun — yin or yang, indicating whether the qi of the season is rising or receding.
2. Ju number (1–9) — which palace the leading Instrument, Wu (戊), falls into on the earth plate; the whole earth plate unfolds from there.
3. Yuan — the upper, middle or lower period of the current solar term, which is what determined the Ju number.

Everything else — the Nine Stars, Eight Doors, Eight Deities, the Three Wonders and Six Instruments — is built on top of this setting. Change the Ju and the whole board changes.

You can cast a chart with NPCC's Qi Men chart tool and the header will display the Dun, Ju and Yuan directly.

You do not have to calculate it, but it is reassuring to know the logic is calendrical, not mystical.

1. First determine which solar term the hour falls in (24 in a year).
2. Then determine whether you are in the upper, middle or lower Yuan of that term — decided by the Fu Tou (符頭) of the day pillar (one "hou" every five days, with Jia and Ji days as the Fu Tou), and by the Chai Bu or Zhi Run rules for assigning upper, middle and lower Yuan.
3. Each solar term has fixed Ju numbers for its three Yuan, recorded in traditional tables.
4. The Winter Solstice side is Yang Dun, counting forward; the Summer Solstice side is Yin Dun, counting backward.

So "Yang Dun Ju 3, Upper Yuan" simply says: we are in the yang half of the year, in the first five-day block of this solar term, and on the earth plate the Six Instruments start from palace 3 and are distributed forward while the Three Wonders are distributed in reverse.

Worth noting: the tables mapping solar terms to Ju numbers are recorded in the major Ming–Qing works such as 奇門遁甲統宗 and 御定奇門寶鑑. Consulting the table is the norm; nobody derives it on the spot.

Suppose the header reads Yang Dun Ju 3 · Upper Yuan · Jia-Zi hour · Chief Deity on the Heavenly Hardship Star · Chief Envoy on the Hurt Door, and you look at one palace. Note this: the Ju and Yuan only decide the earth-plate layout; the Chief Deity star and Chief Envoy door are determined by the palace occupied by the leader of the ten-day cycle to which the hour pillar belongs (here Jia-Zi), not by the Ju and Yuan. Read it in a fixed order every time:

Note what the Ju number did and did not do. It only decided that Wu falls in palace 3 and that the earth plate is distributed from there — that is the entire contribution of "Yang Dun Ju 3." It does not by itself tell you anything auspicious or inauspicious. Meaning emerges from reading the layers in the table above.

A practical reading of this palace: an eastern matter carrying fast, slightly abrasive qi, with the Chief Deity paying attention, but the only mode of action is the Hurt Door — better suited to contending, pursuing debts or competing than to signing and settling. This is a hint about timing and direction, not a verdict.

Think of the Dun and Ju as the seating plan, not the conversation.

• The Ju fixes the earth plate: the Three Wonders and Six Instruments each take their palace.
• The leader of the ten-day cycle (one of the Six Jia) to which the hour pillar belongs determines the Chief Deity and Chief Envoy; the Chief Deity star follows the hour stem to its palace, while the Chief Envoy door is rotated by the hour count, forward in Yang Dun and backward in Yin Dun, then laid over the fixed earth plate.
• Yin Dun and Yang Dun also determine whether certain layers rotate forward or backward — which is precisely the key point of the hour-based rotating-plate Qi Men that NPCC uses.

So if two people cast charts for the same hour and one has the wrong Ju, every single palace will differ. When beginners reach contradictory conclusions, it is usually not poor interpretation but a wrong chart setting. Check the header before you interpret.

One sentence, because it is not as serious as beginners fear: in joining the solar terms to the five-day Three Yuan cycle, history offers two treatments, the Chai Bu method (拆補法) and the Zhi Run method (置閏法), which yield different Ju numbers for a small number of hours each year; this is genuinely disputed with no settled verdict. NPCC's tools use one consistent method; see the dedicated Library article if you want the detail.

There is a bigger divergence too: rotating plate versus flying plate, and the rules for lodging the Central Palace stem. NPCC uses hour-based rotating-plate Qi Men throughout the site, so the lessons stay consistent.

• "Yang Dun is auspicious, Yin Dun is inauspicious." No. These are only the seasonal directions of forward and reverse counting; neither is auspicious or inauspicious in itself.
• "A bigger Ju number is stronger." No. Ju 9 is not better than Ju 1; the number marks the starting palace, not a score.
• "The Ju changes every day." It changes with each Yuan, about every five days; the whole chart changes with each two-hour period.
• "If I can't calculate the Ju I can't read a chart." The ancients compiled tables for exactly this reason. Your attention belongs on the palaces, doors, stars and deities.
• "Yang Dun starts on January 1." Yang Dun starts at the Winter Solstice and Yin Dun at the Summer Solstice — by solar term, not by calendar date.