Heavenly Stems and Earthly Branches Hours: Conversion Steps

The conversion from the clock time on a birth certificate to the hour pillar involves several steps, and their order is fixed: first restore standard time by removing daylight saving time, then unify the time zone, then convert to apparent solar time, and only then consult the hour table. Each step changes the input for the next, so treating them as interchangeable will produce a different result.

四项校正，先后有序

The four corrections are not of equal status. Daylight saving time is a legal offset applied to the clock. Time zone is a geographical and administrative convention. Apparent solar time depends on longitude and the equation of time. The hour table is the final lookup that assigns a 时辰 based on local solar time. The sequence matters because each stage operates on the output of the previous one. If the clock time is 14:30 under daylight saving time, subtracting one hour gives 13:30 standard clock time. Only then can a time-zone correction be considered. If the birth place and the time zone used for the record differ, they must first be brought to the same basis before comparison. After that, the longitude correction and the equation of time are added to obtain apparent solar time. The resulting value is what should be looked up in the twelve-branch hour table.

第一步：夏令时

For births recorded under daylight saving time, the first step is to subtract one hour from the recorded clock time. This applies to people born between 1986 and 1991 whose birth time was written down as the clock time in use at that moment. The hour saved by daylight saving time is a legal artifact, not a solar fact. If it is not removed before the later steps, it will be carried into the time-zone and longitude calculations as though it were real time. The one-hour subtraction should be done only when the record is known to use daylight saving time. If the recorded time is already standard time, this step is not needed. The historical range 1986 to 1991 is given as the period when this adjustment is relevant for records in mainland China.

第二步：时区

After daylight saving time has been removed, the second step is to make the time-zone basis explicit. If the place of birth and the time zone used for the recorded time are not the same, convert them to one common frame before doing anything else. For example, a birth may occur in Xinjiang but be recorded in Beijing time, or a record may use a local time zone that differs from the standard meridian of the region. The comparison should be made only after both sides are expressed in the same time-zone terms. The goal is not to change the actual moment of birth, but to know which standard time corresponds to the record. Without this step, a difference of one or more whole hours can enter the calculation and shift the hour pillar.

第三步：经度与均时差

The third step converts the unified clock time into apparent solar time. Apparent solar time has two components. The first is the longitude correction: for every degree of longitude difference, the time differs by about four minutes. A birth place east or west of the time-zone meridian will be ahead of or behind the mean clock time by that amount. The second is the equation of time, which arises from the earth’s elliptical orbit and axial tilt. Over the course of a year it swings between roughly minus fourteen minutes and plus sixteen minutes. These two components are added together. Their combined effect can reach several tens of minutes. This is why a birth record that looks safely inside an hour may still be near a boundary once apparent solar time is computed. The apparent solar time is the input for the hour table.

最后才查时辰表

Only after the above steps are complete should the hour table be consulted. The twelve divisions are: 子 from 23:00 to 1:00, 丑 from 1:00 to 3:00, 寅 from 3:00 to 5:00, and so on in sequence until 亥 from 21:00 to 23:00. The times written in this table are local solar times, not clock times. A clock reading of 23:10 does not by itself guarantee a 子 hour; if the clock time still contains daylight saving time or is expressed in a different time-zone frame, or if the longitude and equation of time have not been applied, the local solar time may be different. The table should be entered with the corrected apparent solar time. For the site’s charting engine, the input fields are Gregorian year, month, day, hour, minute, and sex. The engine interprets the hour and minute as Beijing clock time and does not accept longitude. Therefore any daylight saving time removal, time-zone adjustment, longitude correction, and equation-of-time adjustment must be done as input preparation before the values are entered. The engine will not perform these corrections internally.

次序颠倒会得到什么结果

When the order is reversed, the most common result is that the one-hour daylight saving subtraction and the longitude correction are either deducted twice or cancel each other. Suppose a user first applies a longitude correction to a clock time that is still one hour ahead because of daylight saving time. The longitude correction is then computed from the wrong clock reading. Later the user may subtract the daylight saving hour, or may not, because the first correction has already changed the number. The two offsets can reinforce each other or erase each other depending on their signs, and the final time can land in the neighbouring hour branch. The same risk appears when the equation of time is applied before the time zone is unified. If the user consults the hour table before these corrections, the table simply returns the branch for whatever number it is given, which may be a clock number rather than a solar number. The error is usually one adjacent 时辰, but it is an error of category: the input was not the quantity the table expects.

When the birth moment falls in the middle of a 时辰, the combined size of these corrections will generally not change the hour pillar. The corrections amount to tens of minutes at most, and the middle of a two-hour branch is far enough from both edges. In such cases, even if the steps are skipped or done out of order, the assigned branch may remain the same. The problem appears only when the birth time is close to a boundary. Near 1:00, 3:00, 5:00, and the other division lines, a difference of ten or twenty minutes can move the result from one hour branch to the next. For those cases, the corrections need to be handled one by one and in the fixed order. The entry is not that the corrections are always necessary, but that when they are necessary, their order is part of the method.