This Shabbat is Shabbat Mevarchim ("the Shabbat that blesses" the new month): a special prayer is recited blessing the Rosh Chodesh ("Head of the Month") of the upcoming month of Iyar, which falls on Monday and Tuesday of the following week.
Prior to the blessing, we announce the precise time of the molad, the "birth" of the new moon. See molad times.
It came to pass on the eighth day (Leviticus 9:1)
That day took ten crowns: It was the first day of creation (i.e., a Sunday), the first for the offerings of the nesi'im (tribal heads), the first for the priesthood, the first for [public] sacrifice, the first for the fall of fire from heaven, the first for the eating of sacred food, the first for the dwelling of the Divine Presence in Israel, the first for the priestly blessing of Israel, the first day on which it was forbidden to sacrifice to G‑d anywhere but in the Sanctuary, and the first of months.
(Talmud, Shabbat 87b)
That day was as joyous to G‑d as the day on which heaven and earth were created.
(Talmud, Megillah 10b)
https://w2.chabad.org/media/pdf/14405.pdf
