"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 the luni-solar calendar, 24 Solar Terms were also necessary for assigning ordinary and leap months. Each 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.
| Name | λ | Explanation |
|---|---|---|
| 土用 "Doyou" | 27°, 117°, 207°, 297° | "Doyou" is the almost 18-day period before "Risshun", "Rikka", "Risshuu", and "Rittou". The start of the "Doyou" period is shown in the calendars. |
| 節分 "Setsubun" | - | The day before "Risshun". Originally, we had "Setsubun" for each season, but only spring "Setsubun" remains nowadays. |
| 彼岸 "Higan" | - | "Higan" is the 7-day period centered around "Shunbun" or "Shuubun". The start of the "Higan" period is shown in the calendars. |
| 八十八夜 "88 Ya" | - | The 88th day from "Risshun". Caution for the late frost. |
| 入梅 "Nyuubai" | 80° | About 10 days before "Geshi". Times for the rainy season. |
| 半夏生 "Hangeshou" | 100° | About 10 days after "Geshi". Times to end planting rice. |
| 二百十日 "210 Ka" | - | The 210th day from "Risshun". Times when the storms come frequently. |