Calculating the new moon – Ask the Rabbi
Q. How can the proclamation of a new month have been based on witnesses seeing the new moon if Jonathan says in I Samuel 20, “Tomorrow is the new moon”? Doesn’t this indicate that there was a system of calculation?
A. A means of calculation preceded the fixing of Rosh Chodesh by eye-witness testimony, so that when problems arose with the eye-witness method, calculation was resumed. It must have been used during the 40 years in the wilderness since the clouds of glory would have precluded seeing the sky.
