What Is True Solar Time? Why Qi Men Charts Must Use It

What Is True Solar Time?

True Solar Time is the time system in which noon is defined by the sun actually crossing your local meridian — in other words, “sundial time.” The standard clock time of any country (Beijing Time, US Eastern Time, etc.) is a mean solar time anchored to one reference meridian, and for most locations it does not equal the true local solar time.

Why Charts Must Be Corrected

Qi Men Dun Jia and BaZi both cast from the Chinese double-hour (Earthly Branch hour) as the smallest unit. If the hour boundary is judged wrongly (for example, 23:00 marking the switch to the Zi hour), the entire chart changes — the classic “wrong hour, wrong chart” failure.

The gap between true solar time and clock time has two components:

Longitude difference: every degree away from your time zone’s reference meridian shifts solar time by 4 minutes. Ürümqi (about 87.6°E) runs roughly 2 hours 10 minutes behind Beijing clock time.
Equation of Time: a seasonal deviation caused by Earth’s elliptical orbit, fluctuating between −14 and +16 minutes through the year.

Example: a user in Xinjiang consults at 15:30 Beijing time — apparently the Shen hour. But the true solar time is about 13:20, which is actually the Wei hour. The focus symbols and formations of the two charts are completely different.

How to Get Your True Solar Time

Formula: True Solar Time = clock time + (local longitude − reference meridian) × 4 minutes + Equation of Time.

Manual calculation is tedious. The Qi Men Dun Jia AI charting tool reads your longitude via GPS or manual input (western longitudes supported) and applies the full correction automatically before casting, so the chart is accurate at the source.