About 24 Solar Terms


Summer, 5th "Setsu". when the sun reaches 75° in longitude. Grain in Ear; Time to plant grains.
Summer, 5th "Chuu". when the sun reaches 90° in longitude. Summer Solstice; Length of day becomes longest.

"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.