About 24 Solar Terms

February

"Risshun"

Spring, 1st "Setsu". when the sun reaches 315° in longitude. Beginning of Spring; Coldest days are almost over and we can feel the sign of spring.

"Usui"

Spring, 1st "Chuu". when the sun reaches 330° in longitude. Rain Water; It becomes warmer. Snow and ice starts melting and snow becomes rain.

"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.