Ancient Chinese had no watches. So how did they make appointments?
They watched shadows. Where the sundial's gnomon fell — or the angle of a tree's shadow on the ground — was their hour. Combining the path of the sun across the sky with the night-time positions of the moon and stars, they divided the entire 24-hour day into 12 segments, each two hours long.
This is the shichen (时辰) system.
Each segment is named by an Earthly Branch: zi, chou, yin, mao, chen, si, wu, wei, shen, you, xu, hai. They aren't just abstract time labels — each shichen has its own ancient name describing what was naturally happening at that moment in human and animal life.
This article covers three things: the complete shichen reference chart, the famous early-zi vs late-zi debate in Bazi practice, and where AstroBazi's algorithm lands on it.
1. The 12 Chinese Double Hours — Complete Reference Chart
| Shichen | Modern Time | Ancient Name | What Was Happening |
|---|---|---|---|
| Zi (子) | 23:00 – 01:00 | Yeban (midnight) | Deepest darkness; yin peaks, yang begins to rise |
| Chou (丑) | 01:00 – 03:00 | Jiming (cock's crow) | The first rooster crows; the world is still |
| Yin (寅) | 03:00 – 05:00 | Pingdan (dawn) | Eastern sky begins to brighten |
| Mao (卯) | 05:00 – 07:00 | Richu (sunrise) | The sun crosses the horizon |
| Chen (辰) | 07:00 – 09:00 | Shishi (mealtime) | When the ancients ate breakfast |
| Si (巳) | 09:00 – 11:00 | Yuzhong (mid-morning) | Sun climbs the southeast sky |
| Wu (午) | 11:00 – 13:00 | Rizhong (noon) | Sun directly overhead; yang energy peaks |
| Wei (未) | 13:00 – 15:00 | Rizhi (afternoon decline) | Sun begins its descent westward |
| Shen (申) | 15:00 – 17:00 | Bushi (afternoon meal) | When the ancients ate again |
| You (酉) | 17:00 – 19:00 | Riru (sunset) | Sun sinks below the horizon |
| Xu (戌) | 19:00 – 21:00 | Huanghun (dusk) | Twilight; lamps are lit |
| Hai (亥) | 21:00 – 23:00 | Renjing (settling) | People retire; heaven and earth rest |
Each segment corresponds to a specific position of the sun in the sky — not an abstract number on a clock. This is why shichen connect naturally to astronomy (sun shadows), nature (animal habits), and human routine (meals, sleep, work).
2. Why 12 Segments — Not 10 or 24?
Three layers of reasoning:
Cosmic rhythm. A day equals one rotation of the Earth. The ancients split it evenly into two halves (day and night, six segments each), totaling 12 — symmetrical with the yin-yang balance.
Pairing with the Earthly Branches. Chinese calendars use 12 Earthly Branches to mark months, directions, and zodiac animals. Splitting a day into 12 segments lets one Earthly Branch govern each segment, locking the entire space-time system together.
Astronomical observability. Two hours is long enough for the human eye to track meaningful changes in the sun's shadow or stars; short enough for daily life to be precisely organized.
3. Early Zi vs Late Zi: Bazi's Most Famous Debate
The Zi hour straddles midnight. So: does 23:00-24:00 belong to today's Zi or tomorrow's Zi? Chinese Bazi practitioners have argued this for centuries. Three positions:
- Early-zi school: The new day starts at 23:00. The day pillar flips at 23:00, and the entire Zi hour (23:00-01:00) belongs to the next day
- Late-zi school: Midnight (00:00) is the true start of a new day. The entire Zi hour (including the 00:00-01:00 early zi) still belongs to the previous day
- Divided-zi (compromise) school: The day pillar flips at midnight 00:00 (using the modern calendar boundary), but the hour-stem already follows the next day's derivation from 23:00 onward. This is the standard among modern Bazi software
AstroBazi's algorithmic position
We use the divided-zi approach — the third (compromise) school above.
In practice: suppose you were born at 23:30 on June 15.
| Component | How it's calculated | Result |
|---|---|---|
| Day Pillar | Midnight boundary; still belongs to June 15 | June 15's day pillar (does not flip to June 16) |
| Hour Pillar branch | After 23:00 → Zi | Zi |
| Hour Pillar stem | Derived from June 16's stem (Five-Mouse Rule) | Taken from the next day's stem table |
This is why a chart at 23:30 (late zi) and a chart at 00:30 the next morning (early zi) share the same Earthly Branch (Zi) but have different Heavenly Stems.
If your teacher's lineage takes a different position: this article doesn't render a verdict — the debate has roots in classical texts on multiple sides. Our algorithm makes a clear engineering choice; it isn't a judgment. If you need to chart by a different school, take our result as a reference and adjust the Hour Pillar by hand.
4. How Shichen Shape Your Bazi Hour Pillar
The Hour Pillar = the heavenly stem and earthly branch of the shichen you were born in. In other words: the two-hour window of your birth determines the last of the four pillars in your Bazi chart.
But note: the "time" here is not the number on the clock, but the actual position of the sun in the sky. Even if you know you were born "at 7:00 AM sharp," clock-time 7:00 and the actual start of the Chen hour can differ by several to tens of minutes — which is why AstroBazi defaults to true solar time.
See our companion article: True Solar Time vs Clock Time.
5. How to Use the Shichen System Today
Not for fortune-telling — for understanding the natural energy rhythm of a day.
Traditional Chinese medicine (TCM) maps each shichen to a meridian:
- Yin hour (3-5 AM) — Lung meridian: deep breathing in early morning is most expansive
- Mao hour (5-7 AM) — Large Intestine meridian: bowel movement is smoothest after waking
- Wu hour (11 AM-1 PM) — Heart meridian: yang peaks; ideal for decisive action
- You hour (5-7 PM) — Kidney meridian: storage time; favor stillness
- Zi hour (11 PM-1 AM) — Gallbladder meridian: deep sleep matters most
You don't have to follow this prescriptively. But it points to one truth: humans are not islands disconnected from the natural rhythm. The ancient Chinese organized daily life around the shichen because they wanted to breathe in sync with heaven and earth. This tradition has survived 3,000 years not because it's superstition — because it captures a real pattern.
Closing
The shichen is a way of seeing time — not by mechanical ticks, but by where the sun and stars actually are in the sky.
It gives Bazi the foundation of the Hour Pillar, and gives modern readers a lens for reflecting on the rhythm of their own day: which segment of the day are you currently in? Is your energy in sync with this moment of heaven and earth?
Want to see which pillar your birth moment falls into? Your Day Pillar, Month Pillar, and Hour Pillar together describe who you are. Calculate your free Bazi chart →
Further reading:
- True Solar Time vs Clock Time: Why Your Bazi Chart Should Use the Sun — why the shichen must be measured by true solar time
- Earthly Branches and the Chinese Zodiac — the other dimension of the Earthly Branches (space and zodiac)
- What's Your Day Master? Bazi's 10 Personality Types, Explained — find the protagonist of your Bazi chart