Vernal Equinox Day is a public holiday in Japan which occurs on March 20 or 21, and became a public holiday in 1948. Before that, this day was called Sunki Koreisai, or Vernal Festival of Past Emperors, and was used to worship the past emperors, as well as the imperial family since the Meiji Era.
Vernal Equinox Day celebrates the spring equinox. It is one of the two days of the year where the daylight and night-time are of equal lengths, the other day being the Autumnal Equinox Day.
Japanese families usually use this day to clean the house, similar to the spring cleaning in western countries. People also go out to appreciate the pleasant weather, as well as the blooming of nature after a long winter.