True Solar Time 真太阳时
Zhēn Tài Yáng Shí · Clock time corrected to where the sun actually is above your birthplace.
What it means
True solar time is the time shown by a sundial: noon is when the sun crosses the meridian of that exact spot. Civil clock time differs from it for two reasons — the time zone is a political band that can be far from your longitude, and the earth's orbit is elliptical, so the sun runs up to about sixteen minutes fast or slow across the year. That second correction is the equation of time.
Why it matters
The day and hour pillars are computed from solar time, not clock time, so the correction can change a chart. A birth at 23:10 clock time in western China can be before 23:00 solar time, which moves the hour pillar and possibly the day pillar with it. Any calculator that ignores longitude is guessing for anyone not born near the centre of their time zone.
| Birth city | Clock time | True solar time | Correction |
|---|---|---|---|
| London, United Kingdom | 12:00 | 10:59 | -61 min |
| Los Angeles, United States | 12:00 | 11:07 | -53 min |
| Beijing, China | 12:00 | 10:46 | -74 min |
| New York, United States | 12:00 | 11:04 | -56 min |
Where this site uses it
The chart tool asks for a birth city, converts the clock time to true solar time using that longitude and the equation of time, and shows the size of the correction it applied.