The equinox in the northern hemisphere happens twice a year, around the 20 March (spring equinox) and the 22 September (autumn equinox).
The spring equinox marks the beginning of astronomical spring when we get nearly equal hours of day and night, and from this day onwards, the day is longer than the night. The autumn equinox marks the start of autumn as the night becomes longer than the day.
See the current view from Meteosat-11 on our Earth view stream over the Atlantic Ocean (https://www.eumetsat.int/real-time-imagery/earth-view )
