Understanding True Solar Time
True solar time tracks the day by the sun’s actual path. We use algorithms to recreate sundial readings, giving your BaZi analysis a more accurate baseline. Get it right, and your BaZi chart readings will be far more precise.
What Is True Solar Time
True solar time mimics what an ancient sundial would show, calculated from the sun’s actual position rather than modern standard time. Understanding this difference is key to accurate BaZi analysis.
Mean Solar Time
Modern standard time. It assumes the sun moves at a constant speed across the sky, dividing the day into exactly 24 hours.
True Solar Time
Time calculated from the sun’s actual position, accounting for Earth’s elliptical orbit and axial tilt.
True solar time varies slightly each day (by up to 30 minutes), while mean solar time sticks to a strict 24-hour cycle. That variation is exactly what lets true solar time track the sun’s real movement.
Historical Context
Ancient cultures tracked time by the sun’s position. The sundial, one of the oldest timekeeping tools, is a direct application of true solar time. This ancient wisdom still guides our astrological readings today.
Sundial Timekeeping
Sundials measure the sun’s exact position, making them the original true solar time clocks.
Origins of BaZi
Ancient scholars built the BaZi system around solar timekeeping, making true solar time its traditional foundation.
How It’s Calculated
Calculating true solar time comes down to two factors: longitude correction and the equation of time. Once you grasp these, converting standard time to true solar time is straightforward.
Longitude Correction
Earth’s rotation means the sun reaches different longitudes at different times. China uses UTC+8 (120°E) as standard, so other locations need a longitude adjustment.
Equation of Time
Earth’s elliptical orbit and tilted axis make the sun’s apparent speed across the sky vary. The equation of time accounts for this variation.
Earth travels in an elliptical orbit, moving faster when it’s closer to the sun and slower when it’s farther away.
Earth’s axis is tilted at 23.5°, which shifts the sun’s apparent path across the sky.
Equation of Time Calculator
Pick any date to see the equation of time and how much true solar time differs from mean solar time. Run the numbers to fine-tune your BaZi analysis and see the concept in action.
Select a Date
Equation of Time Demo
See how Earth’s orbit changes through the seasons and where the equation of time comes from. Follow along with this interactive demo to make complex astronomy easy to grasp.
Winter (Jan–Feb)
Earth moves faster in its orbit. After one full rotation, the sun hasn’t quite caught up to yesterday’s position, so the day runs a bit longer. This makes the equation of time negative.
How It Applies to BaZi
In BaZi, an accurate birth hour is everything. Using true solar time aligns your reading with ancient timekeeping methods, giving you much more precise results.
Pinpoint the Hour Pillar
Precise birth times lead to a more accurate hour pillar, directly affecting how the stems and branches are calculated.
Boost Accuracy
Improves the accuracy of your BaZi analysis, especially if your birth time falls right on the boundary between two hours.
When to Use It
Decide whether to use true solar time based on how precise you need your reading to be. Apply it where it counts to get the most out of your analysis.
Highly Recommended
Your birth time falls right on an hour boundary, so enabling this will give you a much more accurate reading.
Optional
Skip it if you’re just browsing or don’t need pinpoint accuracy.
Not Needed
Your birth time is well away from any hour boundary, so you can safely leave this off for casual use.
Get a Professional BaZi Analysis
Ready to put the theory into practice? Try a real BaZi analysis today and let ancient wisdom guide your modern life.