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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 for Spring

Risshun1st Setsu315° Coldest days are almost over and we can feel the sign of spring.
Usui1st Chuu330° It becomes warmer. Snow and ice starts melting and snow becomes rain.
Keichitsu2nd Setsu345° Insects come out of hibernation.
Shunbun2nd Chuu Length of day and night becomes nearly equal.
Seimei3rd Setsu15° Everything looks fresh and pure.
Kokuu3rd Chuu30° Spring rain showers for grains.

24 Sekki for Summer

Rikka4th Setsu45° We feel the sign of Summer.
Shouman4th Chuu60° Everything grows.
Boushu5th Setsu75° Time to plant grains
Geshi5th Chuu90° Length of day becomes longest.
Shousho6th Setsu105° Times when the rainy season ends and it becomes hot
Taisho6th Chuu120° Hottest days

24 Sekki for Fall

Risshuu7th Setsu135° Times when we feel the sign of fall
Shosho7th Chuu150° Times when we feel less heat
Hakuro8th Setsu165° White dew stays on the grass.
Shuubun8th Chuu180° Length of day and night becomes nearly equal.
Kanro9th Setsu195° Cold dews drops on wild grasses.
Soukou9th Chuu210° Times when frost falls

24 Sekki for Winter

Rittou10th Setsu225° Times when we feel the sign of winter
Shousetsu10th Chuu240° Chilly Season. Rain becomes Snow.
Taisetsu11th Setsu255° Snow starts falling
Touji11th Chuu270° Times when the length of a day becomes shortest
Shoukan12th Setsu285° Start of cold season
Daikan12th Chuu300° 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.

Doyou Setsubun Higan 88 Ya Nyuubai Hangeshou 210 Ka
Doyou27°, 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.
Nyuubai80° In the old days, Mizunoe after Boushu. Times when rainy season comes.
Hangeshou100° In the old days, it was the 10th day from Geshi.
210 Ka- The 210th day from Risshun.