Exact Solar-Term Boundary Times in Bazi
Determine a Bazi chart on a solar-term date by comparing the birth instant with the exact astronomical crossing rather than the date label.
Overview
A solar term begins at one calculated instant, not at midnight for an entire calendar date. For a birth near a Jie, first resolve the recorded local time through the birthplace’s historical time zone, then compare that unique instant with the same year’s solar-longitude crossing. Before the crossing the previous Bazi month remains in force; at or after it the new month applies under the declared inclusivity rule. Li Chun may also change the Year Pillar in systems that use it as the Bazi year boundary, so the Year and Month Pillars must be recomputed together when necessary.
At a glance
- Boundary form
- One astronomical instant
- Comparison basis
- Birth instant and crossing in one timeline
- Before a Jie
- Previous Bazi month
- At or after a Jie
- New month under the saved rule
- Li Chun sensitivity
- Year and Month Pillars may both change
- Unsafe shortcut
- Assigning the whole term date to the new pillar
The printed solar-term date is only a locator
Calendars often display the local date on which a term occurs. The astronomical definition, however, is the moment apparent solar longitude reaches the target degree.
Two births on that displayed date can fall on opposite sides of the crossing. Date-only assignment therefore loses the information most likely to change a near-boundary Month Pillar.
- Retrieve the year-specific crossing timestamp.
- Keep the source precision visible.
Convert the birth and the term to one continuous timeline
Interpret the birth record with the historical time-zone rule for its location and date, including any daylight-saving ambiguity. Convert both the birth and term crossing to the same time standard before comparing them.
Do not compare a UTC ephemeris timestamp directly with an unconverted local clock. The display zone may change the written date but not the ordering of the two instants.
- Resolve gaps and overlaps before comparison.
- Compare instants, not formatted clock strings.
Recompute every pillar that depends on the crossed boundary
A regular Jie changes the Month Branch and its derived Month Stem. At Li Chun, a system using Li Chun as the year boundary also changes the Year Pillar, and the new Year Stem becomes the input to the Month Stem rule.
The calculation must state whether equality belongs to the new interval. At ordinary timestamp precision, exact equality is rare, but the convention remains part of a reproducible engine.
- Update dependent stems after the boundary.
- Save the inclusivity convention.
Return labeled candidates when the evidence cannot resolve the side
If the birth time is approximate or the historical offset is unresolved and the possible interval straddles the crossing, calculate both distinct outcomes. Label the range and assumption supporting each result.
Do not choose the chart that produces a more attractive reading. The uncertainty comes from input evidence, and the output should show exactly which pillar is sensitive to it.
- Transform the full uncertainty interval.
- Deduplicate candidates with identical Four Pillars.
Sources and editorial basis
- Hong Kong Observatory: The 24 Solar Terms香港天文台的年度節氣資料提供精確交節日期時間，支持以瞬間而非整個民用日期判定交界前後An official astronomical explanation of the 24 solar terms, their 15-degree divisions along the ecliptic, and the alternating major and minor terms.
- IANA Time Zone Database出生地歷史時區把本地出生紀錄還原為唯一時間軸瞬間，才能與以 UTC 表示的節氣交接安全比較The maintained reference for historical local-time rules, UTC offsets, and daylight-saving transitions by location.
- OpenFate Editorial Methodology產品在候選範圍跨越節入時保留兩側結果，並同步重算月支、月干及立春所影響的年柱OpenFate separates deterministic chart calculation, traditional interpretation, and modern editorial explanation.