"24 Sekki" or 24 Solar Terms are traditional ways of expressing seasons in Japan and China. Each term is defined by the ecliptic longitude of the Sun (λ). For example, "Shunbun" is the time when the longitude of the Sun becomes 0°, and "Shuubun" is when the longitude becomes 180°.
In luni-solar calendar era, 24 Solar Terms were also necessary for deciding when to insert leap month. A year has four seasons, and each season has 3 "Setsu" and 3 "Chuu" arranged alternately.
| Name | Month | λ | Explanation |
|---|---|---|---|
| 立春 "Risshun" | 1st "Setsu" | 315° | Beginning of Spring; Coldest days are almost over and we can feel the sign of spring. |
| 雨水 "Usui" | 1st "Chuu" | 330° | Rain Water; It becomes warmer. Snow and ice start melting and snow becomes rain. |
| 啓蟄 "Keichitsu" | 2nd "Setsu" | 345° | Insects Awakening; Insects come out of hibernation. |
| 春分 "Shunbun" | 2nd "Chuu" | 0° | Spring Equinox or Vernal Equinox; Length of day and night becomes nearly equal. |
| 清明 "Seimei" | 3rd "Setsu" | 15° | Fresh Green; Everything looks fresh and pure. |
| 穀雨 "Kokuu" | 3rd "Chuu" | 30° | Grain Rain; Spring rain showers for grains. |
| Name | Month | λ | Explanation |
|---|---|---|---|
| 立夏 "Rikka" | 4th "Setsu" | 45° | Beginning of Summer; Times when we can feel the sign of summer |
| 小満 "Shouman" | 4th "Chuu" | 60° | Lesser Fullness; Everything grows. |
| 芒種 "Boushu" | 5th "Setsu" | 75° | Grain in Ear; Times to plant grains |
| 夏至 "Geshi" | 5th "Chuu" | 90° | Summer Solstice; Length of day becomes longest. |
| 小暑 "Shousho" | 6th "Setsu" | 105° | Lesser Heat; Times when the rainy season ends and it becomes hot. |
| 大暑 "Taisho" | 6th "Chuu" | 120° | Greater Heat; Hottest days |
| Name | Month | λ | Explanation |
|---|---|---|---|
| 立秋 "Risshuu" | 7th "Setsu" | 135° | Beginning of Autumn; Times when we can feel the sign of autumn |
| 処暑 "Shosho" | 7th "Chuu" | 150° | End of Heat; Times when we feel less heat |
| 白露 "Hakuro" | 8th "Setsu" | 165° | White Dew; White dew stays on the grass. |
| 秋分 "Shuubun" | 8th "Chuu" | 180° | Autumnal Equinox; Length of day and night becomes nearly equal. |
| 寒露 "Kanro" | 9th "Setsu" | 195° | Cold Dew; Cold dews drops on wild grasses. |
| 霜降 "Soukou" | 9th "Chuu" | 210° | First Frost; Times when frost falls |
| Name | Month | λ | Explanation |
|---|---|---|---|
| 立冬 "Rittou" | 10th "Setsu" | 225° | Beginning of Winter; Times when we can feel the sign of winter |
| 小雪 "Shousetsu" | 10th "Chuu" | 240° | Light Snow; Chilly Season. Rain becomes snow. |
| 大雪 "Taisetsu" | 11th "Setsu" | 255° | Heavy Snow; Snow starts falling. |
| 冬至 "Touji" | 11th "Chuu" | 270° | Winter Solstice; Length of day becomes shortest. |
| 小寒 "Shoukan" | 12th "Setsu" | 285° | Lesser Cold; Start of cold season |
| 大寒 "Daikan" | 12th "Chuu" | 300° | Greater Cold; Coldest days |
"Zassetsu" or Supplementary Solar Terms are additional terms for seasons that complement 24 Solar Terms. "Doyou" and "Higan" shows the start day of "Doyou" and "Higan" period, respectively.
| Name | λ | Explanation |
|---|---|---|
| 土用 "Doyou" | 27°, 117°, 207°, 297° | In the old days, "Doyou" is the 18 day period before "Risshun", "Rikka", "Risshuu", and "Rittou". |
| 節分 "Setsubun" | - | The border of seasons. Originally, we had 4 "Setsubun" for each season, but only spring "Setsubun" remains nowadays. The next day of "Setsubun" is "Risshun". |
| 彼岸 "Higan" | - | "Higan" is the 7 day period from 3 days before "Shunbun" (or "Shuubun") to 3 days after "Shunbun" (or "Shuubun"). 1st day of "Higan" is called "Higan no Iri", and the last day of "Higan" is called "Ake". |
| 八十八夜 "88 Ya" | - | The 88th day from "Risshun". Times when frost is fewer. |
| 入梅 "Nyuubai" | 80° | In the old days, "Mizunoe" after "Boushu". Times when rainy season comes. |
| 半夏生 "Hangeshou" | 100° | In the old days, it was the 10th day from "Geshi". |
| 二百十日 "210 Ka" | - | The 210th day from "Risshun". |