Clocks follow administrative meridians; heaven and earth follow the sun overhead. Every degree of longitude and every day of Earth's orbit shifts the hour a little. A few minutes can move your hour pillar across a boundary.
Apparent solar time follows the Sun's local position. This optional correction lets you compare time conventions. Whether to use it in a chart is a choice of interpretive school, not an astronomical requirement for every charting system.
Clocks follow civil time zones and, where applicable, daylight saving. Local mean solar time depends on longitude. Beijing standard time uses UTC+8 with 120° E as its reference, while places at other longitudes have different local mean solar times.
Apparent solar time is measured by the local solar hour angle. Its difference from mean solar time is the equation of time. The Sun crossing the local meridian marks apparent solar noon, which does not always coincide with noon on a clock.
These synthetic examples use the site's current engine and city-center longitudes. UTC offsets already include daylight saving; it is not deducted again.
| Gregorian clock input | Longitude / Actual UTC offset | Longitude / UTC correction; equation of time | Apparent solar time |
|---|---|---|---|
| Kashgar2000-06-01 14:00:00 | 75.99° E UTC+8 | -176.04 min 2.17 min | 2000-06-01 11:06:08 Wu hour |
| Urumqi1990-08-15 10:30:00 | 87.62° E UTC+9 | -189.53 min -4.09 min | 1990-08-15 07:16:22 Chen hour |
| Los Angeles1985-07-04 09:00:00 | 118.24° W UTC−7 | -52.96 min -4.07 min | 1985-07-04 08:02:58 Chen hour |
Same-engine examples check the site's stated convention; they are not an independent astronomical accuracy test.
Formula and time-zone references: NOAA's published formula (conversion reference; its equation-of-time formula differs from ours) · IANA Asian time-zone history, including China's DST rules
This table uses the listed standard UTC offsets and shows longitude-only corrections to mean solar time, not complete apparent solar time. The full conversion also needs the equation of time for the date. If the clock used daylight saving, enter its actual offset.
| City | Longitude | Zone | Versus zone clock | Typical pitfall |
|---|---|---|---|---|
| KashgarXinjiang | 75.99° E | UTC+8 | about 176 min slow | Longitude only: 14:00 → about 11:04, already in the Wu hour. Add the date's equation of time for the full result. |
| UrumqiXinjiang | 87.62° E | UTC+8 | about 130 min slow | Clock 13:00 is about 10:50 mean solar, still the Si hour; mean solar noon falls near 14:10 on the clock |
| LhasaTibet | 91.10° E | UTC+8 | about 116 min slow | Clock 12:30 is about 10:34 mean solar, the Si hour is not over |
| KunmingYunnan | 102.70° E | UTC+8 | about 69 min slow | |
| LanzhouGansu | 103.80° E | UTC+8 | about 65 min slow | |
| ChengduSichuan | 104.07° E | UTC+8 | about 64 min slow | Clock 11:30 is about 10:26 mean solar, late Si hour, not yet Wu |
| ChongqingChongqing | 106.55° E | UTC+8 | about 54 min slow | Clock 23:40 is about 22:46 mean solar, still the Hai hour, not yet Zi |
| GuiyangGuizhou | 106.70° E | UTC+8 | about 53 min slow | |
| Xi'anShaanxi | 108.93° E | UTC+8 | about 44 min slow | Clock 23:20 is about 22:36 mean solar, still the Hai hour, not yet the late Zi hour |
| NanningGuangxi | 108.32° E | UTC+8 | about 47 min slow | |
| GuangzhouGuangdong | 113.27° E | UTC+8 | about 27 min slow | Clock 09:10 is about 08:43 mean solar, still the Chen hour |
| Hong KongHong Kong | 114.17° E | UTC+8 | about 23 min slow | |
| WuhanHubei | 114.30° E | UTC+8 | about 23 min slow | |
| ZhengzhouHenan | 113.65° E | UTC+8 | about 25 min slow | |
| BeijingBeijing | 116.40° E | UTC+8 | about 14 min slow | Clock 11:05 is about 10:51 mean solar, still the Si hour, not yet Wu |
| TianjinTianjin | 117.20° E | UTC+8 | about 11 min slow | |
| JinanShandong | 117.00° E | UTC+8 | about 12 min slow | |
| NanjingJiangsu | 118.78° E | UTC+8 | about 5 min slow | |
| FuzhouFujian | 119.30° E | UTC+8 | about 3 min slow | |
| HangzhouZhejiang | 120.15° E | UTC+8 | about 1 min fast | Within a minute; the clock usually serves as is, but check the equation of time near a boundary |
| ShanghaiShanghai | 121.47° E | UTC+8 | about 6 min fast | About 6 minutes fast; a clock time of 10:56 sits on the edge of the Wu hour, check the equation of time |
| TaipeiTaiwan | 121.57° E | UTC+8 | about 6 min fast | |
| ShenyangLiaoning | 123.43° E | UTC+8 | about 14 min fast | |
| HarbinHeilongjiang | 126.63° E | UTC+8 | about 27 min fast | Clock 10:40 is about 11:06 mean solar, already the Wu hour |
| SingaporeSingapore | 103.85° E | UTC+8 | about 65 min slow | Singapore keeps UTC+8, so clock 12:00 is about 10:55 mean solar, still the Si hour |
| Kuala LumpurMalaysia | 101.69° E | UTC+8 | about 73 min slow | Kuala Lumpur keeps UTC+8, so clock 13:00 is about 11:47 mean solar: the Wu hour has begun while the clock shows one o'clock |
| BangkokThailand | 100.50° E | UTC+7 | about 18 min slow | |
| TokyoJapan | 139.69° E | UTC+9 | about 19 min fast | |
| SydneyAustralia | 151.21° E | UTC+10 | about 5 min fast | |
| VancouverCanada | 123.12° W | UTC−8 | about 12 min slow | |
| Los AngelesUnited States | 118.24° W | UTC−8 | about 7 min fast | At the listed UTC−8, longitude only: 12:00 → about 12:07. Use the actual offset during daylight saving. |
| TorontoCanada | 79.38° W | UTC−5 | about 18 min slow | |
| New YorkUnited States | 74.01° W | UTC−5 | about 4 min fast | At the listed UTC−5, longitude only: 12:00 → about 12:04. Use the actual offset during daylight saving. |
| LondonUnited Kingdom | 0.13° W | UTC+0 | about 1 min slow |
Coordinates refer to city centers. Mainland Chinese cities default to Beijing-time records; manually check the offset if the record used Xinjiang local time. Overseas offsets here exclude daylight saving, whose adjustment is not always one hour.
Mainland China observed daylight saving in 1986–1991, starting in May in 1986 and April in the following five years, and ending in September. If the birth clock had been advanced, enter UTC+9; do not both enter +9 and subtract another hour. The dates below come from the runtime's IANA time-zone rules.
| Year | Start (clocks +1 h) | End (clocks back) | Note |
|---|---|---|---|
| 1986 | 5/4 | 9/14 | Start: 02:00 advances to 03:00. End: 02:00 returns to 01:00. |
| 1987 | 4/12 | 9/13 | Start: 02:00 advances to 03:00. End: 02:00 returns to 01:00. |
| 1988 | 4/17 | 9/11 | Start: 02:00 advances to 03:00. End: 02:00 returns to 01:00. |
| 1989 | 4/16 | 9/17 | Start: 02:00 advances to 03:00. End: 02:00 returns to 01:00. |
| 1990 | 4/15 | 9/16 | Start: 02:00 advances to 03:00. End: 02:00 returns to 01:00. |
| 1991 | 4/14 | 9/15 | Start: 02:00 advances to 03:00. End: 02:00 returns to 01:00. |
Mainland China has not observed DST since 1992. Clock changes create skipped or repeated times, so a date alone cannot identify the offset. Check the separate histories of Hong Kong, Macau, Taiwan and overseas locations.
Earth's orbit is not a perfect circle and the ecliptic is tilted against the equator, so true solar time swings back and forth against mean time over the year. This curve is computed day by day by the site's engine: correcting only for longitude and ignoring the month can still cost a whole Chinese hour at a boundary.
This approach emphasizes the Sun's position at the birthplace and corrects for longitude and the equation of time before charting. It also needs an explicit clock record, time zone, location and day-boundary convention.
Other schools use the civil time in the birth record without solar correction. When comparing charts, identify their inputs and rules first; differences do not necessarily indicate a software error.
Where Guanyitang standsGuanyitang keeps solar-time correction optional and publishes the correction terms and approximation. The day pillar changes at 00:00; the hour stem at 23:00–23:59 uses the next day's stem. Keep the original record and chosen convention when comparing charts.
For two inputs five minutes apart, the answer depends on whether they cross an hour boundary. The complete solar correction can also include much larger longitude and UTC-offset differences. Chinese hours change at odd-numbered hours; our day pillar changes at 00:00, while the late Zi hour uses the next day's stem.
Compare the calendar, clock time, longitude, actual UTC offset, daylight-saving treatment, solar-time setting and equation-of-time approximation. Then compare the Zi-hour and day-boundary conventions. Different school conventions are not necessarily programming errors.
Our day pillar changes at 00:00. At 23:00–23:59 it still belongs to the current day, but the hour stem is derived from the next day's stem. Solar correction can cross either boundary, so the date, day pillar and hour pillar are compared separately.
Establish a plausible clock-time range first, then check whether its endpoints cross an hour boundary. Calculation does not remove uncertainty in the original record. A vague description or a single chart cannot establish an exact birth minute.
Enter the local clock time at the birthplace and its Gregorian date; do not first convert it to Beijing time. City selection supplies a date-level default offset. Near clock changes, with uncertain historical records or with a special local time convention, manually verify the actual UTC offset at birth.
Now that the light of your birth moment is clear, the next step is to see how this pillar interacts with the rest of your chart.
Your birth date, longitude, time zone and the true solar time switch are carried across so nothing needs retyping. If you have not converted yet, this returns you to the form above.