Sukuyo lunar fortnight: white and black halves
A Sukuyo lunar fortnight in T1299 assigns lunar days 1–15 to the white half and 16–30 to the black half; it is a calendar index, not a Moon angle.
Overview
Use the converted lunar day to find the half-month number. Day names and astronomical phase angles remain separate quantities.
At a glance
- White
- Lunar days 1–15
- Black
- Lunar days 16–30
- Day 16
- Black fortnight day 1
Find the lunar day first
Use the day supplied by the calendar conversion. Do not derive it directly from the Gregorian day number.
The month may end before day 30; the calendar decides which dates exist.
Number within the fortnight
Days up to 15 retain their number. For later days, subtract 15: lunar day 18 is black-fortnight day three.
The same within-fortnight number can occur in both halves of a month.
Read the day name separately
The product’s 15-name list begins 建名, 得財, 威力, 猛武 and 圓滿, then continues through 吉相.
A day name is a traditional identifier, not a guarantee that its literal meaning will occur.
Keep time restrictions distinct
The source lists some daytime or nighttime qualifications in addition to day groups.
That is not permission to invent a birth time, and it does not change the date-only natal input policy.
Do not overstate astronomical precision
This civil-calendar division does not supply the Moon’s exact elongation or a person’s birth longitude.
Use an appropriate astronomical calculation when that different quantity is required.
Check the transition explicitly
Lunar day 15 is white-fortnight day 15; day 16 is black-fortnight day 1; day 30, when the converted month contains it, is black-fortnight day 15.
The labels follow converted lunar days. They do not license adding a nonexistent day 30 or estimating the lunar day from appearance.
Sources and editorial basis
- 宿曜經 · T1299 卷上卷上「宿曜曆經序黑白分品第七」: days 1–15 white, 16–30 black, fifteen day names and separate day/night qualifications.Historical text for mansion names and calendar tables. Its table is not identical to OpenFate’s modern 27-mansion lookup; it does not establish predictive validity.
- OpenFate Sukuyo calculator and calculation conventionEditorial code check 2026-09-10, policy 1.0.0: fortnights; policy.ts, constants.ts, engine.ts and traditional-cycles.ts. Product settings are not an independent historical authority; practical examples are OpenFate editorial applications.Product-specific input and output reference. Editorial checks also inspected policy 1.0.0 and the month-start constants on 2026-09-10; those implementation checks are not an independent traditional authority.