A Vernal Equinox is the time when the sun crosses the plain of the earths equator, making night and day of equal length all over Earth and occurring about March 21st.
first day of fall
March 20 (about: the dates/times vary and are corrected by leap years).
This question is unclear. Is the user asking for times, equinox dates for upcoming years, or a definition?
At the time of the equinox, daytime and night time are as close to equal in duration as they can get.