True Solar Time: Correction by Longitude and Equation of Time

True solar time, 真太阳时, is a time standard that refers to the apparent position of the Sun in the sky at a specific location, rather than the civil clock time used in daily life. In Chinese-metaphysics practice, some schools and software tools apply a correction from clock time to true solar time before determining the hour pillar of a birth chart. This entry explains what the correction is, what it requires, why this knowledge base does not apply it, how tools differ, which pillar it can affect, and how to decide whether to use it.

真太阳时是一项可选校正

The true solar time correction converts clock time into local solar time according to the longitude of the birthplace and the equation of time for the date in question. The result is then used to determine the hour branch, or 时辰. The correction is not a universally mandatory step. It is an optional adjustment that depends on theoretical stance and tool design. Its purpose is to align the recorded birth time more closely with the position of the Sun as observed from the birthplace, rather than with the standard time zone clock.

In practice, the correction answers a specific concern: a civil clock time such as 14:00 may not correspond to the same solar moment in two places that share a time zone but differ in longitude. The true solar time correction tries to remove that discrepancy by calculating the Sun’s local apparent time. It is therefore best understood as a methodological choice, not as an automatic requirement of all Chinese-metaphysics systems.

它需要的输入是什么

To perform the true solar time correction, two inputs are necessary. The first is the longitude of the birthplace. The second is the equation of time for the date of birth. The equation of time is a value that accounts for the difference between apparent solar time and mean solar time caused by the Earth’s orbital eccentricity and axial tilt. Without the longitude, the correction cannot be calculated, because longitude is what determines the offset between local solar time and the standard time zone reference meridian.

This means that any claim to have applied true solar time correction without knowing the birthplace longitude is internally incomplete. The date alone is not enough. The clock time alone is not enough. Longitude is a required input, and the equation of time must be drawn from the relevant date. If a tool does not collect longitude, it cannot genuinely compute true solar time from the supplied data, regardless of what its interface or documentation may state.

本站不做这项校正

This knowledge base engine does not apply true solar time correction. Its input fields are limited to the Gregorian year, month, day, clock hour, minute, and sex. There is no longitude field. Because longitude is absent, the engine cannot calculate true solar time, and by design it does not attempt to do so. The hour pillar is therefore computed directly from the clock time as entered for the birthplace.

This is a stated limitation and a deliberate convention. It does not mean the engine rejects the validity of true solar time in other systems. It means that in this engine the hour pillar follows the recorded clock time, without geographic adjustment. If a user needs a chart based on true solar time, they must either use a tool that supports longitude input or adjust the clock time themselves before entering it, with full awareness of the convention being applied.

不同工具在这一项上的分歧

Different tools handle true solar time in different ways. This is one of the common reasons why two birth charts for the same person may show a different hour pillar even when the other three pillars match. That kind of difference is usually a difference in convention, not a calculation error. One tool may convert to true solar time; another may use civil clock time; a third may offer both options. Each tool is applying its own established rule.

For this reason, when comparing charts from different sources, the first thing to check is not whether one tool is wrong, but whether the tools are using the same time standard. If they are not, then a difference in the hour pillar is expected under certain conditions. This is especially relevant when the recorded birth time is close to the boundary between two hour branches. The disagreement is methodological, and it can be resolved only by making the convention explicit.

这项差异会改变哪一柱

The true solar time correction affects only the hour pillar. It does not alter the year pillar, the month pillar, or the day pillar under the standard calendrical methods used by this knowledge base. The reason is that the correction shifts the time used to assign the hour branch, while the other pillars are derived from the date and the calendrical system rather than from the minute-level time of day.

Moreover, the hour pillar changes only when the clock time is near the boundary between two 时辰. Each 时辰 spans two hours of clock time. If the recorded birth time falls near the start or end of that two-hour period, the correction may push it across the line into the adjacent hour branch. If the birth time falls in the middle of the period, the correction usually does not change the result. The practical impact is therefore narrow: it matters only for births recorded close to an hour boundary.

要不要采用的判断

There is no single consensus across lineages on whether the true solar time correction should be adopted. Different traditions and teachers hold different views. Some regard the correction as necessary for accurate hour assignment. Others regard the civil clock time as sufficient, or they prefer a different reference altogether. Because this is a matter of inherited practice and interpretive stance, the knowledge base does not take a position that one method is universally correct.

What matters more than the choice itself is that a tool states clearly which convention it uses and applies it consistently. If a tool says it uses clock time, it should not silently mix in solar adjustments. If it says it uses true solar time, it should collect the longitude and equation of time needed for the calculation. A stated and stable convention allows users to compare charts meaningfully and to know which variables may have shifted.

Some tools claim to have applied true solar time even when no longitude was obtained. In such cases, the direct question to ask is: which longitude was used. If no longitude was supplied and none can be identified, the claim should be treated as unverified. The absence of that input makes the correction impossible to reproduce. Reproducibility is a basic requirement for any technical adjustment, and longitude is the missing variable that distinguishes a real correction from a label.

When two charts show a difference only in the hour pillar while the year, month, and day pillars are identical, this true solar time convention is the first cause to investigate. It is not the only possible cause, but it is the most likely one when the other three pillars line up exactly. Checking the time standard used by each tool will usually explain the discrepancy. If one tool applied the correction and the other did not, and the birth time was near a boundary, the hour pillar difference can be attributed to that methodological choice rather than to an error in the underlying calendrical data.