True Solar Time in Bazi
Learn how Bazi true solar time combines historical civil time, longitude correction and the equation of time, and when it can change a pillar.
Overview
True solar time, more precisely local apparent solar time, is the time a correctly calibrated sundial would show at the birthplace. OpenFate first resolves the recorded civil time through the historical location time zone, then applies the location’s longitude difference from the zone meridian and the astronomical equation of time. This correction can move a birth across an hour or day boundary, but it is a calculation setting—not proof of a personality or event.
At a glance
- Astronomical term
- Local apparent solar time
- Civil-time input
- Historical local clock resolved to one instant
- Constant component
- Longitude difference from the zone meridian
- Variable component
- Equation of time for the date
- Possible impact
- Hour branch, day boundary or solar date
- OpenFate policy
- Applied explicitly with uncorrected input preserved
Apparent solar time follows the actual Sun at one longitude
The U.S. Naval Observatory defines apparent solar time from the true Sun’s local hour angle. Solar noon occurs when the apparent Sun crosses the observer’s meridian.
Because the Sun’s apparent rate varies through the year, this is not a uniform clock scale. Every calculation therefore needs a date as well as a longitude.
- Treat it as location-and-date specific.
- Do not confuse it with UTC or standard time.
Civil time, longitude and equation of time are separate steps
The recorded local clock is first mapped to an instant using the historical time-zone and daylight-saving rule. Longitude correction converts zone-based time toward local mean solar time.
The equation of time then relates mean solar time to apparent solar time. Keeping each component visible prevents double-correcting daylight saving or longitude.
- Resolve the historical civil offset first.
- Expose each signed correction in the result.
Only a crossed boundary changes the computed symbols
A correction of several minutes may leave all pillars unchanged. It matters when the corrected time crosses an Hour-Branch boundary, the selected Zi-day boundary or a local date.
The original civil time, corrected time, solar date, coordinates and method version should remain available so another calculator can reproduce the result.
- Report whether any pillar actually changed.
- Preserve both original and corrected timestamps.
True solar time does not make an interpretation scientifically proven
The correction is an astronomical time transformation used by a declared Bazi convention. It does not validate traditional symbolic interpretation as modern science.
Uncertain birthplace or birth time can exceed the size of the correction. A responsible page discloses that uncertainty instead of advertising false precision.
- No certainty claim from extra decimals.
- No event prediction from the correction alone.
Sources and editorial basis
- U.S. Naval Observatory: The Equation of Time美國海軍天文台說明視太陽時、平太陽時、經度時差與均時差，提供真太陽時各計算成分的天文依據An official astronomical explanation of apparent solar time, mean solar time, longitude offsets, and the equation of time.
- IANA Time Zone DatabaseIANA Time Zone Database：真太陽時前先還原出生地當日民用 UTC 偏移與日光節約時間，避免把現代偏移套回歷史The maintained reference for historical local-time rules, UTC offsets, and daylight-saving transitions by location.
- OpenFate Editorial Methodologytests/bazi/test-true-solar-time.ts 分開保存原始民用時刻、經度修正、均時差與最終太陽時，並在跨時辰或日界後重算受影響柱OpenFate separates deterministic chart calculation, traditional interpretation, and modern editorial explanation.