403. Blue Moon: The obligation to bring additional offerings on Rosh Chodesh

Just as on Shabbos, as discussed in the previous mitzvah, an additional sacrifice was also offered on Rosh Chodesh, the start of the new month. (Many people translate Rosh Chodesh as “new moon,” but in its current astronomical sense that refers to the time of the month when no moon is visible. We will avoid the use of that phrase in order to avoid confusing two discrete astronomical events.)

The reason for this mitzvah is related to the importance of the moon. Obviously, the moon is important for light at night. And, notably, it affects the Earth’s tides. Historically, the moon has also played a role in navigation, in agriculture, in timekeeping and even in medicine. All of this is possible because the moon is not static; it goes through its phases, waning and waxing. It is God Who set the moon in motion, causing it to renew each month. It is therefore appropriate to bring an extra offering on the day that the moon is renewed, to thank Him for this gift and to recognize that all the goodness the moon brings about comes from Him.

This mitzvah applies when the Temple service is in effect. In the Talmud, it is discussed in tractate Menachos on pages 49a-b. It is codified in the Mishneh Torah in Hilchos Temidin U’Musafin. This mitzvah is #42 of the 248 positive mitzvos in the Rambam’s Sefer HaMitzvos.