True Solar Time Calculator for BaZi Birth Clocks
True solar time corrects the recorded clock for its time-zone offset, longitude and equation of time. Enter east-positive longitude to see each correction and the resulting solar clock.
Apparent solar time 1990-05-15 09:19:31
Mean solar time 1990-05-15 09:15:36 · Historical UTC offset +09:00
Longitude correction -74.40 minutes + equation of time 3.93 minutes = -70.47 minutes.
Longitude correction
The Earth turns one degree in four minutes. Mean solar time is UTC plus four minutes per degree of east longitude. Subtract the recorded clock’s historical zone offset to find its longitude correction.
Equation of time
The apparent Sun moves ahead of or behind the mean solar clock through the year. The fractional-year equation adds this difference in minutes to mean solar time.
Date and hour boundaries
A correction can cross midnight or a two-hour branch boundary. Compare the corrected date and time with the original chart inputs. For repeated daylight-saving clocks, select the earlier or later occurrence.