True Solar Time (真太陽時)
The sun at your birthplace, not the clock on the wall.
In short
True solar time (真太陽時, zhēn tài yáng shí) is the time read from the sun at the birth location rather than from a clock. It differs from clock time by up to about two hours, and Bazi uses it for the hour pillar, so two charts from the same clock minute can differ.
| Characters | 真太陽時 · 真太阳时 |
|---|---|
| Pinyin | zhēn tài yáng shí |
| Group | Reading the chart |
Clocks keep an average time for a whole time zone. The sun does not. Two corrections close the gap, and both are arithmetic rather than judgement.
The first is longitude. The sun crosses one degree of longitude every four minutes, and a time zone is defined by a single meridian. Beijing time uses 120°E, so a birth in Beijing at 116.4°E runs about 14 minutes ahead of the sun, and a birth in Urumqi at 87.6°E runs roughly 130 minutes ahead. China has used a single time zone since 1949 and spans more than 60 degrees of longitude, so in the west the clock and the sun disagree by more than two hours.
The second is the equation of time, which is the difference between the average day a clock measures and the actual day the sun delivers. It swings about 16 minutes forward in early November and about 14 minutes back in mid-February, caused by the earth's elliptical orbit and its axial tilt. Small on its own, and worth adding.
The correction matters in proportion to how close a birth is to a two-hour boundary. A birth at 11:30 clock time is nowhere near one, and the pillar holds. A birth at 12:55 clock time sits five minutes from the boundary, and a 15-minute correction moves it into the next hour and changes the pillar, the hidden stems under it, and every ten god counted from those.
Definitions get you through a chart. Something has to be done with it.
The audit walks the nine areas of a home in the order that matters, with two or three changes per area. It is the practical half of what these terms describe.
Questions people ask about this term
Does Bazi use clock time or the sun?
The sun, in the strict form of the system. The hour pillar is set by true solar time at the birth location, which means correcting clock time for longitude and for the equation of time. Many popular calculators skip both and use clock time directly.
How do I calculate true solar time?
Two steps. Find the difference between your longitude and your time zone's standard meridian, multiply the degrees by four minutes, and subtract it if you are west of the meridian or add it if you are east. Then add or subtract the equation of time for that date, which runs from about minus 14 to plus 16 minutes across the year.
Does true solar time matter if I was born mid-window?
Usually not. A correction of up to half an hour only changes the hour pillar for births within about half an hour of a two-hour boundary. If your birth time is comfortably inside a window, the pillar is safe; if it is near one, the correction decides which pillar you get.
This page has no affiliate links and nothing to sell. The tables here are fixed by the tradition and you can check any of them against a printed almanac. What a chart means for a person is a reading of that tradition, not a finding, so treat it as a way to think about a situation rather than a prediction.