A year was divided into 24 solar terms on the traditional Japanese calendar. Geshi (夏至) literally meannig “to reach summer” is the 10th solar term. It usually begins around June 21st, the longest day of the year when the Sun is farthest north in the northern hemisphere and Sun gets the highest meridian altitude. As the axis of the Earth declines 23.5 degrees towards or away from the Sun ecliptic, the meridian altitude of the Sun differs from season to season. It is this declination that creates seasonal changes on the Earth.

The summer solstice marks the first day of the summer. Different from the winter solstice, there are relatively few social activities held in Japan. Farmers usually start rice planting on the day of Han-geshi, the 11th day from the summer solstice. In the Kansai region, people eat octopus on this day in hope that the roots of rice plants will grow steadily like octopus legs. In Sanuki area in Kagawa Prefecture, July 2nd is Day of Sanuki-udon Noodle, because farmers usually entertain assistant workers with Sanuki-udon noodles after rice planting.