Vernal Equinox Day春分の日[ Shunbun no hi ]

Vernal Equinox Day (春分の日, Shunbun no Hi) is a public holiday in Japan that occurs on the date of the Northward equinox in Japan Standard Time (the vernal equinox can occur on different dates in different time-zones), usually March 20 or 21. The date of the holiday is not officially declared until February of the previous year, due to the need for recent astronomical measurements.

from Vernal_Equinox_Day (Wikipedia) CC BY SA 3.0