Question: what is the first day of nisan 2020?
Answer: According to this for 2020 (5780) both systems have a short year, with Nisan starting with the new moon just after the spring equinox. That astronomical conjunction of the moon and the sun will occur at 11:29 am on March 24th (28th day of the Jewish month Adar) Jerusalem time, with the sun setting just before 6 pm.