To determine the correct date, several pieces of information need to be obtained, using astronomical tables:

(1.) Date and time of the Vernal (Spring) Equinox of the given year.

(2.) Date and time of the New Moon preceding the Equinox.

(3.) Date and time of the New Moon following the Equinox.

(4.) Date and time of the New Moon which occurs closest to the Equinox.

(5.) To find Nisan 1, add two hours and twenty-one minutes to account for the time difference at the meridian in Jerusalem.

Data for 2025

(1.) Date and time of the Vernal (Spring) Equinox: March 20 at 9:03 a.m.

(2.) Date and time of the New Moon preceding the Equinox: February 28 at 12:46 a.m.

(3.) Date and time of the New Moon following the Equinox: March 29 at 10:59 a.m.

(4.) Date and time of the New Moon which occurs closest to the Equinox: March 29 at 10:59 a.m.

(5.) Add two hours and twenty-one minutes to determine the beginning of Nisan 1 at the meridian in Jerusalem: March 29 at 1:20 p.m.

To determine the date of Nisan 1, let us remember that the Jewish day runs from 6:00 p.m. in the evening to 6:00 p.m. the following evening, unlike our customary midnight to midnight reckoning. By knowing the exact time in which Nisan 1 begins at Jerusalem in a given year, we are able to determine the date of Nisan 1 for that year.

For 2025, Nisan 1 begins on March 29 at 1:20 p.m. in Jerusalem. Backing up to the nearest preceding 6:00 p.m. indicates that Nisan 1 starts at 6:00 p.m. on March 28.

To determine the date of Nisan 14, the date to celebrate the Memorial, we need to count forward thirteen full days, which brings us to April 10. So, Nisan 14 starts at 6:00 p.m. on Thursday, April 10, your local time.

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Source: Astronomical Tables of the Sun, Moon, and Planets by Jean Meeus (Willmann-Bell, Inc.; 1983), pp. 3-43, 4-20.

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