Rosh Chodesh Musaf-offering
Requires Beit HaMikdash
BaMidbar 28:11 At the beginning of your months you shall bring a olah-offering to Hashem, two young bulls, one ram, seven yearling lambs, [all] without blemish.
We are commanded offer a sacrifice on every Rosh Chodesh (New Moon) in addition to the daily olah-offering, this being the Musaf (Additional)-offering of the Rosh Chodesh. In this connection it may be noted that, the Jewish calendar being essentially based upon the rotation of the moon around the earth, the appearance of the new moon, following the period of its invisibility (approx. 2 days), was always marked by a festival-day in Yisrael. The Musaf-offering brought on that day emphasized the importance of the occasion.