Solar vs Lunar: The Professional Standard for 12 Day Officers
Bottom line: 12 Day Officers are keyed to the solar month (the Sun’s position), not the lunar month. If you use lunar months, your officers drift and your timing fails.
Why this matters
The Officer is computed by a single rule: (Day Branch − Month Branch) mod 12.
If you pick the wrong Month Branch—because you used lunar months—you corrupt the result.
Deals close late. Conversations misfire. Easy fix: use solar months.
Solar terms in 60 seconds
λ⊙ (solar longitude)
The Sun’s apparent ecliptic longitude runs 0°→360° yearly.
Principal terms
Divide the year into 12 × 30° segments (principal solar terms).
Solar months
These 30° segments define the solar months (节气月) used for the Month Branch (月建).
How the Month Branch (月建) is determined
Compute λ⊙ for the instant you care about; map it to a 30° bin. 寅月 starts near 立春. A compact mapping:
| λ⊙ range (deg) | Month Branch | Order (寅起) |
|---|---|---|
| [315°, 345°) | 寅 | 0 |
| [345°, 15°) | 卯 | 1 |
| [ 15°, 45°) | 辰 | 2 |
| [ 45°, 75°) | 巳 | 3 |
| [ 75°, 105°) | 午 | 4 |
| [105°, 135°) | 未 | 5 |
| [135°, 165°) | 申 | 6 |
| [165°, 195°) | 酉 | 7 |
| [195°, 225°) | 戌 | 8 |
| [225°, 255°) | 亥 | 9 |
| [255°, 285°) | 子 | 10 |
| [285°, 315°) | 丑 | 11 |
Once you have the Month Branch index (0‥11, 寅起) and the Day Branch index (寅起),
the Officer is immediate: (Day − Month) mod 12.
Boundary behavior (duplicates are normal)
At a solar-month rollover, both Branch indices advance by one day-to-day.
The difference (day − month) stays the same.
Expect two identical Officers back-to-back.
If your almanac forbids this, they’re using the wrong basis.
Zi-hour day start (23:00)
What changes
Zi-hour affects the Day Branch (which local date you count) if your lineage flips the day at 23:00.
What doesn’t
The Month Branch is solar and continuous. Zi-hour does not alter month boundaries.
Timezones and locality
- λ⊙ is astronomical and absolute; the instant of a boundary is global.
- Local date/time presentation differs by timezone. Before the boundary instant → old month; after → new month.
- If you straddle a boundary overnight, re-check once the Sun crosses the threshold.
Audit any almanac in 3 checks
- Ask: “Is your Month Branch solar-term based?” If not, walk away.
- Boundary test: Do they allow duplicate Officers across month rollover? They should.
- Transparency: Do they show λ⊙ or clearly declare the method? If not, assume handwaving.
Common mistakes and myths
- “Use the lunar month.” — Wrong. Officers are solar.
- “No two identical Officers in a row.” — Wrong. They repeat at rollover.
- “Midnight flip only.” — Not universal. Zi-hour (23:00) is valid in many lineages.
Applications (business & relationships)
- Control the boundary: Settle terms before rollover; launch after if the new Officer favors you.
- Exploit duplicates: When an Officer repeats, you get a two-day window: day 1 setup → day 2 strike.
- Stack signals: Officer + Day Pillar for tone; don’t fight seasonality.
