Core answer: The 24 solar terms (二十四节气) divide the sun's ecliptic year into 24 slices of 15° each — Lichun (Feb 3–5), Chunfen (Mar 20–22), Qingming (Apr 4–6) … each fixed to the solar calendar within ±2 days. Created ~2,000 years ago for farming, they still drive Qingming Festival, the "counting-nine" cold calendar, and dog-days (三伏) scheduling. UNESCO listed them in 2016.
The 24 terms at a glance
| Season | Terms (Gregorian dates) |
|---|---|
| Spring | Lichun Feb 3–5 · Yushui Feb 18–20 · Jingzhe Mar 5–7 · Chunfen Mar 20–22 · Qingming Apr 4–6 · Guyu Apr 19–21 |
| Summer | Lixia May 5–7 · Xiaoman May 20–22 · Mangzhong Jun 5–7 · Xiazhi Jun 21–22 · Xiaoshu Jul 6–8 · Dashu Jul 22–24 |
| Autumn | Liqiu Aug 7–9 · Chushu Aug 22–24 · Bailu Sep 7–9 · Qiufen Sep 22–24 · Hanlu Oct 8–9 · Shuangjiang Oct 23–24 |
| Winter | Lidong Nov 7–8 · Xiaoxue Nov 22–23 · Daxue Dec 6–8 · Dongzhi Dec 21–23 · Xiaohan Jan 5–7 · Dahan Jan 20–21 |
The three living traditions
1. Qingming (Apr 4–6). The only solar term that is also a statutory festival — tomb sweeping plus spring outings. It's solar-fixed, so it never drifts like lunar festivals.
2. Dog days 三伏. Summer's hottest 30–40 days, counted from the 3rd 庚 day after Xiazhi (mid-July to mid-August). 2025's 三伏: Jul 20 – Aug 18. "Winter illness treated in summer" (冬病夏治) plasters follow this calendar.
3. Counting nines 数九. Nine 9-day periods from Dongzhi: "一九二九不出手，三九四九冰上走" — the coldest stretch (三九/四九) lands mid-to-late January; 九九 ends around Mar 12, plums bloom, spring plowing starts.
Worked examples
Example 1 — Tea picking. 明前龙井 ("before Qingming") means leaves picked before Apr 4–6 — the solar-term boundary is why "Mingqian" commands 2–3× prices over 雨前 (before Guyu, Apr 20).
Example 2 — Travel planning. Chunfen/Qiufen (equinoxes) have exactly 12-h days worldwide; Dongzhi in Beijing: ~9.3 h daylight; Xiazhi: ~15 h. Photography golden hours shift accordingly.
Example 3 — Health customs. "头伏饺子二伏面" — the dog-days eating calendar anchors to 三伏 dates, computable each year from Xiazhi + the sexagenary day count.
Common mistakes and myths
- "Solar terms are lunar" — they're pure SOLAR phenomena; the lunar calendar borrows them, which is why Qingming stays Apr 4–6 while Spring Festival wanders a month.
- Equinox = equal day/night everywhere — almost: atmospheric refraction adds a few minutes of daylight; true 12:00:00 equality happens a few days before/after.
- Lichun = spring weather — it's astronomical spring; Beijing averages still below freezing. Phenological spring (5-day avg ≥ 10 °C) arrives ~40 days later.
- Dog days always 30 days — 30 or 40 depending on the 庚-day count; 2025 has 30.
- "Outdated superstition" — solar terms encode orbital geometry with 15° precision; they're astronomy, not folklore, and still the most elegant seasonal calendar in use.