What Are Solar Terms?
The Solar Terms (Jieqi), or the twenty-four Solar Terms, are a calendrical system devised in ancient China that divides the year into 24 equal segments based on the sun's position along the ecliptic. Each Solar Term spans approximately 15 days, reflecting seasonal changes and the rhythm of waxing and waning of the qi of heaven and earth.
In Bazi, Solar Terms are not merely a calendrical concept — they are the core temporal framework for chart casting: the Month Pillar begins and ends at the "Jie" (nodes), and the Year Pillar begins and ends at the Start of Spring (Lichun).
Complete Table of the Twenty-Four Solar Terms
The twenty-four Solar Terms are divided into 12 "Jie" (nodes) and 12 "Qi" (midpoints), arranged in alternating order:
| No. | Solar Term | Type | Month Branch | Approx. Gregorian Date |
|---|---|---|---|---|
| 1 | Minor Cold | Jie | Chou month start | Jan 5–7 |
| 2 | Great Cold | Qi | Chou mid-month | Jan 20–21 |
| 3 | Start of Spring | Jie | Yin month start | Feb 3–5 |
| 4 | Rain Water | Qi | Yin mid-month | Feb 18–20 |
| 5 | Awakening of Insects | Jie | Mao month start | Mar 5–7 |
| 6 | Spring Equinox | Qi | Mao mid-month | Mar 20–21 |
| 7 | Pure Brightness | Jie | Chen month start | Apr 4–6 |
| 8 | Grain Rain | Qi | Chen mid-month | Apr 19–21 |
| 9 | Start of Summer | Jie | Si month start | May 5–7 |
| 10 | Grain Full | Qi | Si mid-month | May 20–22 |
| 11 | Grain in Ear | Jie | Wu month start | Jun 5–7 |
| 12 | Summer Solstice | Qi | Wu mid-month | Jun 21–22 |
| 13 | Minor Heat | Jie | Wei month start | Jul 6–8 |
| 14 | Great Heat | Qi | Wei mid-month | Jul 22–24 |
| 15 | Start of Autumn | Jie | Shen month start | Aug 7–9 |
| 16 | Limit of Heat | Qi | Shen mid-month | Aug 22–24 |
| 17 | White Dew | Jie | You month start | Sep 7–9 |
| 18 | Autumn Equinox | Qi | You mid-month | Sep 22–24 |
| 19 | Cold Dew | Jie | Xu month start | Oct 7–9 |
| 20 | Frost Descent | Qi | Xu mid-month | Oct 23–24 |
| 21 | Start of Winter | Jie | Hai month start | Nov 7–8 |
| 22 | Minor Snow | Qi | Hai mid-month | Nov 22–23 |
| 23 | Great Snow | Jie | Zi month start | Dec 6–8 |
| 24 | Winter Solstice | Qi | Zi mid-month | Dec 21–23 |
Months change at the Jie: whenever a Jie arrives, the Month Pillar switches to the next month. The Qi (midpoints) do not change the month; they only mark the midpoint of a Month Command.
Solar Terms and the Year Stem-Branch
Start of Spring as the Year's Beginning
In Bazi, the Start of Spring (Lichun) (approximately February 3–5 each year) marks the beginning of the year, not the first day of the lunar new year. Those born before Lichun retain the previous Stem-Branch year in their Year Pillar; those born after Lichun switch to the new year.
Examples:
- 2025-01-20 (Lunar 12th month, 1st day): Lichun has not yet arrived, so the year Stem-Branch remains Jia-Chen
- After 2025-02-03 (post-Lichun): the year Stem-Branch switches to Yi-Si
Calculating the Year Stem-Branch
The Year Stem-Branch cycles every 60 years. The Heavenly Stems (Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui) pair with the Earthly Branches (Zi, Chou, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu, Hai), advancing one position each year. For example:
- Jia-Zi → Yi-Chou → Bing-Yin … and so on.
Solar Terms and the Month Stem-Branch
Months Change at the Jie
In Bazi chart casting, only the 12 Jie determine the switching of the Month Pillar. Each Jie corresponds to a fixed Earthly Branch for the Month Command:
| Jie | Month Branch | Commanding Element |
|---|---|---|
| Start of Spring | Yin month | Wood |
| Awakening of Insects | Mao month | Wood |
| Pure Brightness | Chen month | Earth (late Wood) |
| Start of Summer | Si month | Fire |
| Grain in Ear | Wu month | Fire |
| Minor Heat | Wei month | Earth (late Fire) |
| Start of Autumn | Shen month | Metal |
| White Dew | You month | Metal |
| Cold Dew | Xu month | Earth (late Metal) |
| Start of Winter | Hai month | Water |
| Great Snow | Zi month | Water |
| Minor Cold | Chou month | Earth (late Water) |
Calculating the Month Stem — "Five Tigers Chase the Year" Method
The Month Branch is fixed by Solar Terms, while the Month Stem is determined by the Year Stem, using the mnemonic known as the "Five Tigers Chase the Year" method:
| Year Stem | Yin month Stem starts at | Pattern |
|---|---|---|
| Jia or Ji year | Bing-Yin | Yin month begins at Bing |
| Yi or Geng year | Wu-Yin | Yin month begins at Wu |
| Bing or Xin year | Geng-Yin | Yin month begins at Geng |
| Ding or Ren year | Ren-Yin | Yin month begins at Ren |
| Wu or Gui year | Jia-Yin | Yin month begins at Jia |
From the Yin month stem onward, advance sequentially to obtain the stems for all months of that year:
- For a Jia-Zi year: Yin month = Bing-Yin, Mao month = Ding-Mao, Chen month = Wu-Chen … and so on.
The Critical Role of Solar Terms in Practical Chart Casting
- Determining the Year Pillar: Whether Lichun has passed determines which year Stem-Branch applies.
- Determining the Month Pillar: Whether the relevant Jie has passed at the time of birth determines the Month Stem-Branch. Births just one minute on either side of a Jie boundary can result in a completely different Month Pillar.
- Determining the Start of the Luck Cycle: The starting age of the Luck Cycle is calculated by converting the number of days from birth to the nearest Jie into years; the exact moment of the Jie must be precise.
- Reference for the Human Element Commander: The number of days after the preceding Jie within the month determines which segment — Remaining Qi, Secondary Qi, or Primary Qi — of the Month Command's Hidden Stems is in authority.
The Distinction Between Jie and Qi
- Jie (nodes): The temporal boundaries at which months change. They govern the switching of the Month Pillar and are the most important for Bazi chart casting.
- Qi (midpoints): Mark the midpoint of a Month Command. They do not change the month, though traditional calendrical systems use Qi to determine which lunar month a period belongs to — a logic distinct from Bazi chart casting.
In Bazi, only the Jie are used for changing months, never the Qi. This is a different system from the lunar calendar's rule of "determining months by Qi," and beginners should take special care to distinguish between the two.