Rosh Hashanah 19 - The court sets the time

As we learned earlier, once the court (Sanhedrin) confirms the New Moon, the day becomes the first day of the month (Rosh Chodesh.) The calendar for Shabbat is different. Shabbat comes on the seventh day, and the court has no power to accelerate or delay this. By contrast, the first of the following month comes either twenty-nine or thirty days after the previous. Depending on the court's determination, the exact date for every Holiday, such as Rosh Hashanah and Passover, may change. This setting of the date will affect the dates when people can or cannot do work. It will also affect the dates when they can or cannot eat chametz and should eat matzah.

Therefore, the court would send messengers who would travel to distant lands such as Babylonia and inform the Jewish community about the date when the New Moon was declared. There were a total of six months when this knowledge was necessary. One of them was Elul - because of Rosh Hashanah that followed that month. The other was the month of Tishrei - because of Yom Kippur on the tenth day of Tishrei. Why did they have to trouble the messengers two months in a row, seeing that the month of Elul was almost always twenty-nine days, and thus the month could be calculated directly? In setting the next month, the court took the needs of the whole nation into account. Therefore, they could make the Elul month complete thirty days and delay Rosh Hashanah on rare occasions.

Art: Crescent Moon by Andrew Wyeth