This year Passover begin at sundown on Friday April 19, and
conclude at sundown on Saturday April 27, the end of Shabbat.
The uncertainty surrounding when the Jewish holidays begin
can be chalked up to two main factors:
They begin at sundown and align with the lunar calendar.
Unlike secular holidays, which begin at 12:01 a.m.
on the respective day, Jewish holidays begin at sundown
the night beforehand. So the first full day of a Jewish holiday
isn’t the holiday’s actual beginning.
Another reason for the constant wondering of when Jewish holidays,
in this case specifically Passover,
begin is that the Jewish calendar follows the lunar cycle,
not the solar cycle, as the Gregorian calendar does.
Passover, in accordance with the Hebrew calendar,
spans the 15 to the 22 days of the month, Nissan.
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