Question: what is the first day of nisan?
Answer: Nisan-years begin in the Spring season. Technically, its New Year's Day is the day after the New Moon closest to (within fifteen days before or after) the Spring equinox, when the day and the night is of equal length, set at March 21 in the Gregorian Calendar). It begins the first month, named Nisanu/Nisan/Abib.