About 24 Solar Terms


Spring, 2nd "Setsu". when the sun reaches 345° in longitude. Insects Awakening; Insects come out of hibernation.
Spring, 2nd "Chuu". when the sun reaches 0° in longitude. Spring Equinox; Length of day and night becomes nearly equal.

"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.