Q&A: Fixing the Months by Calculation
Fixing the Months by Calculation
Question
Hello to the Rabbi.
As is well known, Hillel II established the Jewish calendar based on calculating the years, but this wisdom had already been known from earlier times, as Abaye says in the Talmud, tractate Rosh Hashanah.
And likewise, when they sanctified the month based on sighting, they would check the witnesses to see whether they were telling the truth.
And here the son asks: why for years did the people of the Diaspora observe a second festival day, with a blessing and fulfillment of the commandments on both days, just so that they could hear with their own ears
what was already openly known and established—that the month had been sanctified in the Land of Israel?
Answer
The sanctification was not always done in accordance with the calculation. If witnesses did not arrive, they would not sanctify on the first day even if by calculation they knew that was the correct day. There are other reasons as well to deviate from the calculation. What determines it is the actual sanctification by the religious court.