When equinoxes happen

The earth's year is not a consistent 365 days, often there is an extra quarter of a day that accumulates each year which causes the date of the equinox to shift.

Nevertheless, the equinox usually happens to mark the astronomical beginning of spring or autumn, but the meteorological beginning of these seasons are March 1st and September 1st.

This 2021, the spring equinox is bound to happen on March 20th, and the fall equinox to happen on September 22nd.