24 Sekki

24 Sekki is a traditional way of expressing seasons in Japan and 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 Sekki was 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.

[24 Sekki]
Sekki Month λ Meaning
Risshun 1st Setsu 315° Coldest days are almost over and we can feel the sign of spring.
Usui 1st Chuu 330° It becomes warmer. Snow and ice starts melting and snow becomes rain.
Keichitsu 2nd Setsu 345° Insects come out of hibernation.
Shunbun 2nd Chuu Length of day and night becomes nearly equal.
Seimei 3rd Setsu 15° Everything looks fresh and pure.
Kokuu 3rd Chuu 30° Spring rain showers for grains.
Sekki Month λ Meaning
Rikka 4th Setsu 45° We feel the sign of Summer.
Shouman 4th Chuu 60° Everything grows.
Boushu 5th Setsu 75° Time to plant grains
Geshi 5th Chuu 90° Length of day becomes longest.
Shousho 6th Setsu 105° Times when the rainy season ends and it becomes hot
Taisho 6th Chuu 120° Hottest days
Sekki Month λ Meaning
Risshuu 7th Setsu 135° Times when we feel the sign of fall
Shosho 7th Chuu 150° Times when we feel less heat
Hakuro 8th Setsu 165° White dew stays on the grass.
Shuubun 8th Chuu 180° Length of day and night becomes nearly equal.
Kanro 9th Setsu 195° Cold dews drops on wild grasses.
Soukou 9th Chuu 210° Times when frost falls
Sekki Month λ Meaning
Rittou 10th Setsu 225° Times when we feel the sign of winter
Shousetsu 10th Chuu 240° Chilly Season. Rain becomes Snow.
Taisetsu 11th Setsu 255° Snow starts falling
Touji 11th Chuu 270° Times when the length of a day becomes shortest
Shoukan 12th Setsu 285° Start of cold season
Daikan 12th Chuu 300° Coldest days


Zassetsu is another sign of season that complements 24 Sekki. Doyou and Higan shows the start day of Doyou and Higan period, respectively.

Name λ Explanation
Doyou 27°, 117°,
207°, 297°
In the old days, Doyou is the 18 day period before Risshun, Rikka, Risshuu, and Rittou.
Setsubun - The border of seasons. Originally we had 4 Setsubun for each season, but we only refer the spring Setsubun nowadays. The next day of Setsubun is Risshun.
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".
88 Ya - The 88th day from Risshun. Times when frost is fewer.
Nyuubai 80° In the old days, Mizunoe after Boushu. Times when rainy season comes.
Hangeshou 100° In the old days, it was the 10th day from Geshi.
210 Ka - The 210th day from Risshun.