Chinese Double-Hours and the Sun's House: Your Birth Hour Places Your Sun
The BaZi double-hour uses an Earthly Branch and the birth chart's house uses a number, but they describe the same thing: where the Sun was in the sky at the moment you were born. Know the double-hour and you can say roughly which house the Sun is in; look at the Sun's house and you can check whether a birth time was copied down wrong.
Cast your chart to see your double-hour and the Sun's house
Enter your birth date, birth time and birthplace to get your birth chart and BaZi; the calculator works out your true solar time at birth from the chart and compares the double-hour from clock time with the house your Sun is in. Everything is calculated in your browser; nothing is uploaded.
Tropical zodiac, Placidus houses, true node. Enter the local clock time on your birth certificate; daylight saving time is removed automatically from the birthplace's time-zone history, so there is no need to convert it yourself. If your town is not listed, pick the nearest large city.
The Sun passes through all twelve houses every day
A birth chart's houses are fixed to the sky over your birthplace: the 1st house starts at the eastern horizon (the Ascendant) and runs below it, the 4th is under your feet, the 7th at the western horizon, the 10th near the Midheaven overhead. As the Earth turns, the Sun rises in the east, passes overhead and sets in the west, which in house terms means moving backward through the houses: at sunrise it is at the boundary of the 1st and 12th, then passes through the 12th and 11th, reaches the 10th and 9th around noon, the 7th and 6th toward evening, and the 4th and 3rd around midnight.
The twelve houses go round once a day and so do the twelve double-hours, so they look like a one-to-one match. In practice Placidus houses stretch and shrink with season and latitude, so it is not one-to-one: each double-hour concentrates the Sun in two neighboring houses.
The twelve double-hours and the Sun's house
| True solar double-hour | The Sun's two most common houses | Sun vs. horizon |
|---|---|---|
| Zi hour (23:00–01:00) | 4th house 53.5%, 3rd house 46.5% | below |
| Chou hour (01:00–03:00) | 3rd house 53.4%, 2nd house 46.6% | below |
| Yin hour (03:00–05:00) | 2nd house 51.5%, 1st house 48.5% | below |
| Mao hour (05:00–07:00) | 1st house 51%, 12th house 49% | above in 49% |
| Chen hour (07:00–09:00) | 11th house 55.4%, 12th house 44.6% | above |
| Si hour (09:00–11:00) | 11th house 52.4%, 10th house 47.6% | above |
| Wu hour (11:00–13:00) | 9th house 52.1%, 10th house 47.9% | above |
| Wei hour (13:00–15:00) | 8th house 51.7%, 9th house 48.3% | above |
| Shen hour (15:00–17:00) | 7th house 50.3%, 8th house 49.7% | above |
| You hour (17:00–19:00) | 6th house 54.6%, 7th house 45.4% | above in 45.4% |
| Xu hour (19:00–21:00) | 6th house 51.4%, 5th house 48.6% | below |
| Hai hour (21:00–23:00) | 4th house 57.2%, 5th house 42.8% | below |
Taipei, 2,400 birth moments drawn uniformly from 1950–2010 (fixed seed), Placidus houses. Grouped by true solar time (the Sun's actual position), not clock time.
A few patterns stand out. Born from the Chen to the Shen hour (07:00–17:00 true solar time), the Sun is always above the horizon, a day chart; from the Xu to the Yin hour (19:00–05:00) it is always below, a night chart. Only the Mao and You hours cross the horizon depending on the season: in summer the Sun has already risen during the Mao hour, in winter it hasn't. This is also how astrology tells day charts from night charts.
Estimating the rising sign from the double-hour
The rising sign is the sign coming up in the east at birth. At sunrise the Sun sits right on the Ascendant, so people born around the Mao hour often have the same rising sign as Sun sign. After that, the Ascendant moves on by about one sign every two hours:
| True solar double-hour | Most common Ascendant | Second most common |
|---|---|---|
| Zi hour | 9th sign after the Sun (71.3%) | 8th sign after the Sun (15.8%) |
| Chou hour | 10th sign after the Sun (67%) | 9th sign after the Sun (19.4%) |
| Yin hour | 11th sign after the Sun (70.3%) | same sign as the Sun (15.3%) |
| Mao hour | same sign as the Sun (66.5%) | 11th sign after the Sun (17.5%) |
| Chen hour | 1st sign after the Sun (63.7%) | 2nd sign after the Sun (19.2%) |
| Si hour | 2nd sign after the Sun (70.8%) | 1st sign after the Sun (20.3%) |
| Wu hour | 3rd sign after the Sun (64.8%) | 2nd sign after the Sun (20%) |
| Wei hour | 4th sign after the Sun (70.9%) | 5th sign after the Sun (17.2%) |
| Shen hour | 5th sign after the Sun (67%) | 6th sign after the Sun (16.8%) |
| You hour | 6th sign after the Sun (68.1%) | 7th sign after the Sun (20.4%) |
| Xu hour | 7th sign after the Sun (69.5%) | 8th sign after the Sun (15.7%) |
| Hai hour | 8th sign after the Sun (65.5%) | 9th sign after the Sun (22.7%) |
The same 2,400 Taipei charts. "3rd sign after the Sun" means: with the Sun in Aries, the Ascendant is in Cancer (Aries → Taurus → Gemini → Cancer).
For the Mao hour, the rising sign matched the Sun sign in 66.5% of charts. This is only a rough estimate, because the signs take different lengths of time to rise (in Taipei from about an hour and a half to over two hours); for your real rising sign, use the rising sign calculator.
Clock time and true solar time
BaZi hour pillars are usually cast from the clock time on the birth certificate; but since a double-hour originally means the Sun's position, strictly speaking it should use true solar time. Taiwan's standard time is based on 120°E, while Taipei lies at 121.56°E, so the clock runs about six minutes behind the Sun; add the equation of time (which swings by up to about 16 minutes either way over the year) and the two can differ by around twenty minutes.
Same sample; clock time is Taiwan standard time (daylight saving time removed); 802 births fell near a boundary.
So most people need not worry; only those born near an odd-numbered hour (say 10:55 or 13:05) need to consider whether the hour pillar might change. The site's BaZi chart follows the usual convention of clock time, and schools differ on whether to switch to true solar time; for how to convert, see true solar time. The calculator above shows both.
Using the Sun's house to check a birth time
The most practical use of this correspondence is catching mistakes. Common errors in recorded birth times are a.m. and p.m. swapped, a misread 24-hour clock, or daylight saving time forgotten. Cast the chart and glance at the Sun:
- The record says noon, but the Sun is in the 3rd or 4th house (below the horizon): the birth was probably around midnight, with a.m. and p.m. swapped.
- The record says early morning, but the Sun is in the 7th or 8th house: it may have been early evening.
- Born in a summer between 1945 and 1979 in Taiwan and the Sun sits about one house off from what you expect: daylight saving time may have been left in or removed twice; see daylight saving time.
This only catches big errors; it can't fine-tune a birth time to the minute. For that, see birth time correction.
Keep reading
A straight word: a birth chart is a language, not a prophecy
A birth chart draws the sky at the moment you were born so you can talk about personality and life themes in terms of planets, signs and houses. The planetary positions are astronomical fact and can be calculated very precisely; readings such as "Mars in Aries means drive" are astrological tradition, not scientific findings. It is a fine tool for knowing yourself and sorting out your thoughts, but it cannot make decisions for you. Everything on this site is for reference and entertainment only; for health, investment or legal matters, please consult a professional.
Cast your full birth chart
Enter your birth date, time and place to get your Sun, Moon, Ascendant, all ten planets, the twelve houses and the aspects in one go, with a reading for each placement. Everything is calculated in your browser.
Chinese hours and houses FAQ
Born in the Wu hour, which house is my Sun in?
For Taipei, births in the Wu hour (11:00–13:00 true solar time) put the Sun in the 9th house (52.1%) or the 10th house (47.9%). The Sun enters the 9th house only after it passes the Midheaven, so the first half of the Wu hour is mostly the 10th and the second half mostly the 9th.
Are the double-hours and the houses the same thing?
They measure the same thing, the Sun's position in the sky, but divide it differently. Double-hours split the day into twelve equal parts, while Placidus houses stretch and shrink with season and latitude, so the match is not one-to-one; each double-hour concentrates the Sun in two neighboring houses.
Should BaZi use true solar time?
Schools differ. A double-hour originally means the Sun's position, so strictly speaking it should be true solar time, but most BaZi software and practitioners use clock time. In our Taipei sample the two methods gave different double-hours for only 7.3% of births, concentrated near the boundaries.
Can I work out my rising sign from my double-hour?
Only roughly. Born around the Mao hour (sunrise), the rising sign is often the same as the Sun sign, and it moves on about one sign every two hours after that. But the signs take different times to rise, so the exact rising sign still needs your birth time and birthplace.
If I don't know my double-hour, can the Sun's house tell me?
No. The Sun's house itself needs a birth time to calculate. What you can do is the reverse: if you already have a birth time, use the Sun's house to check it for big mistakes such as a.m. and p.m. swapped.