When does Yin Dun begin each year?

Yin Dun begins at the Summer Solstice, not on New Year

Yin Dun begins at the Summer Solstice each year, at the exact astronomical moment of that solar term. It does not start on the Gregorian New Year, Chinese New Year, or any fixed calendar date unless the Summer Solstice happens to fall there.

Why the Summer Solstice is the start

Yin Dun and Yang Dun are the two annual modes in traditional Qi Men Dun Jia that divide the year into two tactical seasons. The Summer Solstice is the turning point when Yin energy is at its peak and the system flips into the Yin Dun mode by classical definition. This is the observable, calculable anchor practitioners have used for centuries: a solar term switch, not a festival or arbitrary civil calendar point.

How to determine the precise start time

Use astronomical ephemeris data for the exact instant the Sun reaches 90 degrees ecliptic longitude, which is the Summer Solstice solar term. Account for your time zone and local longitude. Do not assume June 21 each year because the solstice can fall on June 20, 21, or 22 depending on year and zone. Use an authoritative ephemeris or software that outputs UTC and then convert to local time.

Practical checklist for practitioners

• Obtain the UTC moment of the Summer Solstice for the year from a reliable ephemeris.
• Convert that moment to local time where the event you will chart occurs.
• For any event that occurs at or after that local moment, use Yin Dun methods and placements.
• If an event occurs before that moment on the same civil date, use the outgoing Yang Dun until the solstice instant passes.

What changes when Yin Dun starts

The working mechanics of the chart shift when Yin Dun begins. The Heaven and Earth panels, which are the two layers of placements used to record cosmic and terrestrial positions for a chart, are interpreted differently under Yin Dun rules. Heaven and Earth panels together show the relational overlay used to place the 9 Stars and the 8 Doors for any hour and day, and under Yin Dun their sequencing reverses relative to Yang Dun.

Terminology, explained once and used precisely

The 8 Doors are the categories of possible actions in a palace, representing outcomes like Open, Rest, and Attack. The 9 Stars are the nine energetic qualities that occupy palaces and modify outcomes, for example influences similar to authority, danger, or opportunity. The 8 Gods are moral or spiritual templates that color an action, and they interact with Doors and Stars in the chart. The Three Wonders are the three core alignment checks between Time, Person, and Space that validate a reading. The Six Instruments are the technical operations you apply to transform a layout into a tactical recommendation. Every one of these elements is present in Yin Dun charts, but their orientation and the rules that govern sequencing change when Yin Dun begins.

How sequencing differs in Yin Dun

In Yin Dun, rotation of the 9 Stars across palaces runs counter to the rotation used in Yang Dun. This is not an optional stylistic preference. It affects which Star sits in which palace at the moment you plot the chart, and that placement governs whether a Door is actionable or blocked. The effect cascades because the 8 Doors may gain or lose support from adjacent Stars and from the 8 Gods that occupy nearby palaces. Treat Yin Dun as a mirror of Yang Dun for sequencing rules; if you do not invert sequencing at the Summer Solstice instant, your chart will be systematically wrong for half the year.

Turning rules into decisions

Apply this immediate operational rule: If your planning window falls between the Summer Solstice instant and the subsequent Winter Solstice instant, use Yin Dun. Use Yang Dun only between Winter Solstice and the next Summer Solstice. For campaigns that cross the Summer Solstice boundary, split operations at the exact solstice time and re-evaluate with the new Dun’s placements. Do not batch process an entire campaign to the old Dun simply because the civil month has not changed.

What Yin Dun favors tactically

Yin Dun favors concealment, indirect action, informational control, and structural reorganization rather than frontal assault. This translates into practical choices when the 8 Doors and 9 Stars align under Yin Dun rules. For example, use Doors that support retreat, negotiation, or subterfuge when those Doors are strengthened by favorable 9 Stars and by supportive 8 Gods. Conversely, do not force Open Door actions if the local Stars indicate obstruction; the Yin season amplifies resistance to overt moves.

Decide based on the season of the Dun, not on wishful intent.

Simple mappings you can act on today

When you have a Yin Dun chart in hand, run these checks in order using the Three Wonders and the Six Instruments: Verify the Time, Person, Space alignments. Confirm which 9 Star occupies the target palace. Confirm the 8 Door there. Confirm the 8 God supporting or opposing. Then decide to Engage, Delay, Reposition, or Abandon. Follow the hierarchy strictly because the seasonal Dun determines the baseline probabilities.

Edge cases every competent practitioner must handle

Account for events at midnight around the solstice. Account for locations across the International Date Line where the local date may differ from astronomical UTC. Account for historical charts where classical authors used local apparent solar time; when working historically, replicate the original timekeeping rules. When in doubt, calculate the precise solar term instant and then apply your locality adjustments. There is no substitute for exactitude at the solstice boundary.

Use Yin Dun from the Summer Solstice instant until the Winter Solstice instant when the system flips back into Yang Dun.