Today (April 10th) is the 1st Nissan.
"And the LORD spake unto Moses and Aaron in the land of Egypt, saying,
This month shall be unto you the beginning of months: it shall be the first month of the year to you.
Speak ye unto all the congregation of Israel, saying, In the tenth day of this month they shall take to them every man a lamb, according to the house of their fathers, a lamb for an house: And if the household be too little for the lamb, let him and his neighbour next unto his house take it according to the number of the souls; every man according to his eating shall make your count for the lamb.
Your lamb shall be without blemish, a male of the first year: ye shall take it out from the sheep, or from the goats:
And ye shall keep it up until the fourteenth day of the same month: and the whole assembly of the congregation of Israel shall kill it in the evening." - Exodus 12:1-6
It is the month of Passover.
We even have evidence in the gregorian calendar that spring used to be the New Year - October, November, December come from the 8th, 9th and 10th months.
Technically, this is a little late, as it has been posted after sunset, and we therfore now have the 2nd Nissan - Sorry!