True Solar Time Date Rollover in Bazi
Learn what to recalculate when longitude and equation-of-time corrections move a Bazi birth across midnight or the selected Zi-hour boundary.
Overview
True solar time can fall on the previous or next solar date when the combined longitude correction and equation of time cross a date boundary. That does not rewrite the birth certificate or UTC instant. It creates a derived local apparent-solar reading used only if the chart’s declared method applies solar time to the relevant Bazi boundary. OpenFate preserves both readings and recalculates the Day and Hour Pillars together whenever the configured boundary is crossed.
At a glance
- Original record
- Remains the civil birth date and time
- Derived value
- Local apparent-solar date and time
- Possible crossing
- Midnight or selected 23:00 boundary
- Affected pillars
- Day Pillar and derived Hour Stem
- Required provenance
- Zone, longitude, equation and day-boundary mode
- Method boundary
- Apply only under a declared solar-time policy
A solar-date crossing changes a derived reading, not the source record
The historical zone first maps the civil birth record to one instant. Longitude and equation-of-time corrections then express that same instant as local apparent solar time.
If that derived clock crosses into another date, store both values. The certificate date remains the source; the solar date is a method-specific calculation field.
- Never overwrite the civil record.
- Show the complete correction chain.
The declared day-boundary doctrine still matters
A midnight convention changes the Day Pillar at 00:00, while a Zi-hour convention may change it at 23:00. A corrected value can cross one boundary without crossing the other.
The calculator must apply the saved doctrine after the solar correction and use the resulting effective Day Stem in the Five Rats Method.
- Test the actual configured rollover time.
- Recompute the Hour Stem after a Day-Stem change.
Recalculate all dependent values as one transaction
A new effective date can change the Day Pillar; that can change the Hour Stem even when the Hour Branch remains the same. Other date-indexed relations must use the same result.
Do not patch only the displayed date or Hour Pillar. A consistent engine derives every dependent field from one corrected timestamp and boundary mode.
- Avoid partial pillar updates.
- Version the correction and boundary policy.
Near a boundary, compare methods without declaring one favorable
If the recorded minute, longitude or method is uncertain, show the civil-time and solar-time variants and identify their exact differences.
A date crossing is not proof of a life event, character change or superior chart. It is a sensitivity result created by a declared time model.
- Keep uncertainty visible.
- Do not select the chart by interpretation.
Sources and editorial basis
- U.S. Naval Observatory: The Equation of Time美國海軍天文台區分標準時間、地方平太陽時與地方視太陽時，經度與均時差可使衍生太陽讀數跨越日界An official astronomical explanation of apparent solar time, mean solar time, longitude offsets, and the equation of time.
- IANA Time Zone DatabaseIANA 歷史時區先把原始民用出生紀錄固定為唯一瞬間，太陽時跨日不能反向改寫出生證明日期The maintained reference for historical local-time rules, UTC offsets, and daylight-saving transitions by location.
- OpenFate Editorial Methodology產品保存民用與太陽日期，依已聲明的 00:00 或 23:00 日界重算日柱，並以新日干同步重算時干與依賴欄位OpenFate separates deterministic chart calculation, traditional interpretation, and modern editorial explanation.