True Solar Time Examples: Beijing, Chengdu, and Urumqi

China uses the 120°E Beijing Time standard nationwide, while city longitudes differ. The same clock time therefore receives different solar corrections.

Assumptions

These teaching examples use 12:00 clock time and an equation of time of -9 minutes. The longitude term is 4×(longitude-120°) minutes.

Common errors

• Treating the equation of time as fixed.
• Reversing longitude signs.
• Applying a local-time conversion and longitude correction twice.
• Ignoring a date change.

Workflow

1. Keep the recorded Beijing clock time.
2. Verify city and longitude.
3. Record before and after times.
4. If an hour boundary is crossed, compare both charts.

Worked calculation: Chengdu

Take 12:00 Beijing Time and a teaching longitude of 104.1°E for Chengdu. First find the longitude difference: 104.1° − 120° = −15.9°. Then multiply by four minutes per degree: −15.9 × 4 = −63.6 minutes. Finally add the equation of time for the birth date. If that date’s demonstration value is −3 minutes, estimated apparent solar time is about 10:53. The live feature should use its resolved coordinates and date-specific value; these rounded numbers explain the calculation rather than replace it.

Why the equation of time is not fixed

Earth’s orbital geometry and axial tilt cause apparent solar time to differ from mean solar time by an amount that changes through the year. “Longitude difference × four” is therefore only one component. Never copy the extra minutes from one date to another. Near a traditional-hour boundary, calculate the actual birth date and retain the unrounded result until the final display.

Verify the result on this site

1. Enter the original Beijing civil time and select a supported birthplace in China.
2. Create and save a baseline chart with correction disabled.
3. Enable true solar time and record the displayed corrected timestamp.
4. Check the direction: a place west of 120°E will normally move earlier.
5. If the result crosses an odd-hour boundary, preserve both charts for review.

Scope

The birthplace correction currently supports locations within China only. Availability for mainland China, Hong Kong, Macao, and Taiwan follows the locations offered by the interface. Do not use this feature for overseas births.

Practical questions

Why is Beijing not exactly on Beijing Time’s standard meridian?

The time-zone name describes a national civil standard based on 120°E; it does not mean central Beijing lies on that longitude. Beijing therefore still has a modest longitude correction.

Can I use a city-center longitude for every birth?

It is acceptable for a teaching estimate but can hide several minutes across a large municipality. The live feature should resolve the selected birthplace consistently. Near a boundary, record the actual district or hospital location when known.

Why might another calculator differ by a few minutes?

It may use a different coordinate, equation-of-time approximation, sign convention, rounding stage, or definition of apparent versus mean solar time. Compare intermediate values before deciding that either final number is wrong.

Conclusion

The farther west a Chinese birthplace lies, the larger the typical backward correction from Beijing clock time.