Zassetsu is Japanese original terms that complement 24 Solar Terms.
They were used for farmers to compreghend seasons, and still now they give us a sence of seasons and have a big impact on the seasonal events in Japan.
Here are some of them, which we are familiar with and till strongly connect to our custom.
the perood of 18 days before the beginning of four sesons in 24 solar terms
立春(Risshun - the beginning of spring - approx. 4 Feb)
立夏(Rikka- the beginning of summer - approx. 5 May)
立秋(Risshu- the beginning of autumn - approx. 7 August)
立冬(Ritto- the beginning of winter - approx. 7 November)
＊土用の丑の日(Do-yo no ushi no hi) is the day we have a custom of eating eels.
the day before 立春(Risshun)
＊the day of Bean-throwing tradition
the period of 7days which contains 立春(Risshun) and 立秋(Risshu) in the middle
＊We have a custom to go to our cemetary during this period.
4.八十八夜(Hachi ju hachi ya)
88 days after 立春(Risshun) , which is approx. on 2 May
＊There is a well-known song, saying `Hachi-ju-hachi-ya when summer approaches ...'
80 degrees in the ecliptic longitude, which is approx. on 11 June
＊It literally means `to enter plums'. As this is the season of plums, we use this term to describe the wet season begins.
Similarly, 梅雨(tsu-yu) means the wet season in Japan. `Plum rain' is its literal meaning.