Vernal Equinox Day (春分の日 Shunbun no hi) is a public holiday in Japan that occurs on the date of the vernal equinox in Japan Standard Time (the vernal equinox can occur on different dates in different timezones), usually March 20 or 21. The date of the holiday is not declared official until February of the previous year, due to the need for recent astronomical measurements.
Vernal Equinox Day became a public holiday in 1948. Prior to that it was the date of Shunki kōreisai ( 春季皇霊祭), an event relating to Shintoism. Like other Japanese holidays, this holiday was repackaged as a non-religious holiday for the sake of separation of religion and state in Japan’s postwar constitution.