Standard Meridians in Bazi
Understand how a time zone’s standard meridian anchors longitude correction in Bazi without confusing legal clock time with local solar time.
Overview
A standard meridian is the longitude whose local mean solar time ideally corresponds to a zone’s standard clock. The familiar model assigns fifteen degrees of longitude to one hour, or four minutes per degree, but legal time-zone borders are irregular and historical offsets can change. For a reproducible Bazi conversion, first resolve the date-specific standard offset, derive its reference meridian, then compare that meridian with the birthplace longitude. Daylight-saving time is removed before this step because it is a legal clock shift, not a different solar meridian.
At a glance
- Ideal clock ratio
- 15° longitude per hour
- Time difference
- 4 minutes per degree of longitude
- Reference input
- Date-specific standard UTC offset
- Not the reference
- Daylight-saving clock offset
- Correction sign
- East of meridian later; west earlier
- Interpretive limit
- A coordinate correction, not a symbol
A standard meridian is a clock reference, not a political border
Mean solar time changes continuously with longitude. The idealized zone system chooses a reference longitude for each standard UTC offset, while governments draw legal zone borders around communities rather than exact meridians.
A birthplace can therefore use a legal time zone whose reference meridian is far from its own longitude. The correction measures that geometric difference; it does not replace the historical time-zone lookup.
- Resolve the legal zone before applying longitude.
- Do not infer the zone from longitude alone.
Derive the reference from standard time, then apply four minutes per degree
A standard offset of UTC+8 corresponds ideally to 120° east, and UTC−5 to 75° west. Subtract the reference longitude from the birthplace longitude and multiply the signed difference by four minutes per degree.
A birthplace east of the reference meridian reaches local mean noon earlier, so its mean-solar reading is later than the zone clock; a western birthplace is earlier. Preserve decimal longitude and the signed result.
- Use signed longitude consistently.
- Keep the intermediate meridian and minute correction.
Use the effective standard offset, not a daylight-saving display
Daylight-saving time advances the legal clock but does not move the Sun or the reference meridian. Remove that seasonal shift before deriving the meridian.
Historical regions can also change their base offset. The correct reference is the standard rule attached to the birthplace and date, not the zone’s current offset or a modern map.
- Separate standard and daylight offsets.
- Version the historical time-zone source.
Only a crossed Bazi boundary changes the pillars
Longitude correction first produces local mean solar time; the equation of time may then produce apparent solar time under the selected method. Test the corrected value against the hour, day and exact solar-term boundaries used by the chart.
The correction itself has no element, Ten God or personality meaning. If it does not cross a declared boundary, the Four Pillars remain unchanged even though the calculation record is more precise.
- Name the boundary that changes, if any.
- Do not interpret longitude as fate.
Sources and editorial basis
- U.S. Naval Observatory: The Equation of Time美國海軍天文台說明地方平太陽時與標準時只在定義子午線附近相符，並給出每度經度約四分鐘的換算關係An official astronomical explanation of apparent solar time, mean solar time, longitude offsets, and the equation of time.
- IANA Time Zone DatabaseIANA 歷史時區提供出生日期有效的標準偏移與日光節約轉換；參考子午線不能由現行 UTC 偏移或經度單獨推定The maintained reference for historical local-time rules, UTC offsets, and daylight-saving transitions by location.
- OpenFate Editorial Methodology產品分開保存歷史時區、標準偏移、參考子午線、出生地經度、均時差及跨界結果，且不把地理修正轉譯成命理象徵OpenFate separates deterministic chart calculation, traditional interpretation, and modern editorial explanation.