When is Nisan 14 in 2020 (Jewish Calendar Year 5780)?

New Moon in the Western Sky begins the lunar month.

The Jewish Calendar consists of 12 lunar months of 29.5 days each, bringing the “return of the year” in 354 days, falling short by 11 and one-quarter days of the solar year length.  So the first problem in determining the date is to choose which new moon will mark the first month of the sacred year (as opposed to the start of the agricultural year which is 6 months latter).

In the 4th century of our common era the rabbi Hillel II established an official Jewish Calendar that has been in use since then.  A 13th lunar month is added 7 times in 19 years to make up the shortfall.  The long years (13 months) occur at the end of years 3, 6, 8, 11, 14, 17 and 19 in the cycle, which is named for the Greek astronomer, Meton, who first devised it in the fifth century before our common era.

This cycle pattern is similar to the black keys on the piano, representing the grouping of long years.

Piano Key pattern of 13-month years in 19 year Metonic Cycle

This means that by simply observing the calendar, we can determine which years correspond to this pattern of long years.  Since the 20th century the first year on the Jewish calendar in the 19-year groups began in 1902, and again in 1921, 1940, 1959, 1978, 1997, and 2016. The first 13-month year of the current cycle occurred in 2019, corresponding with C# on the piano scales as year 3.

Jehovah’s Witnesses have followed this same pattern since the first World War.  However, their first year in the cycle occurs 14 years after the Jewish system, or 5 years earlier in the over-lapping scale of time. So in 2020, the Jewish calendar is at year 5 (12 months), while the Witnesses are at year 10 (also 12 months.)  The mis-matches between the two parallel systems occur in years 1, 9 and 12 of the Jewish system, when those years are short, whereas the Witnesses are observing long years 6, 14, and 17 at the same corresponding time.  Likewise, while the Jews are observing adar-adar, their 13th month in their years 3 and 14, Witnesses are starting Nisan a month earlier. This means that although Witnesses claim to follow the Jewish passover for Nisan 14, in 5 out of 19 years, there is a month difference in setting the date for Nisan 14.

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. In order for a star or a dark face moon to be visible, the sun must be at least 8 degrees below the horizon, and the body observed must be 3 degrees above the horizon.  Therefore, the new moon will not be visible in Jerusalem that evening, even with the best weather, and the next day will be the 29th of Adar.

The moon moves to the left of the sun when the sun is high in the sky in its daily arc, or it appears to rise above it at sunset at the rate of one diameter per hour or 0.508 degrees of arc out of 360.  Therefore to separate from the sun by the required 11 degrees, at least 22 hours of time must elapse after the time of conjunction or point of passing in the observed sky.

Sunset the next evening in Jerusalem on March 25th will occur at 5:54 pm local time (GMT+2), when the sun will descend below the horizon. Thirty-two minutes later the sun will be 8 degrees below the horizon, but the lunar month’s astronomical age will be 30.5 hours old, placing the moon about 7 degrees above the horizon, allowing for a visual sighting.  Therefore, Witnesses will start their month of Nisan at sunset on Wednesday March 25th.  This means that Nisan 14 will begin at sunset on Tuesday, April 7th, which is the evening set for the Memorial observance at Kingdom Halls and places of meeting.