Also on your days of rejoicing, at your designated times and on Rosh-Hodesh, you are to sound the trumpets over your burnt offerings and over the sacrifices of your peace offerings; these will be your reminder before your G-d. I am Adonai your G-d.
Numbers 10:10 (CJB)
In ancient times, the new moon was announced by trumpets, messengers, and hilltop fires. Even though the new moon can be precisely calculated, tradition still dictates that the new month is announced and a prayer is recited asking for peace, prosperity, and piety during the coming month.
G-d said, “Let there be lights in the dome of the sky to divide the day from the night; let them be for signs, seasons, days and years; and let them be for lights in the dome of the sky to give light to the earth”; and that is how it was. G-d made the two great lights — the larger light to rule the day and the smaller light to rule the night — and the stars.
Genesis 1:14-16 (CJB)
The concept of a lunar calendar did not originate with Moses. Rather, it was built into the design of the universe. The existence of lunar calendars dates back thousands of years before the giving of the Torah at Sinai.
Adonai spoke to Moshe and Aharon in the land of Egypt; he said,“You are to begin your calendar with this month; it will be the first month of the year for you.
Exodus 12:1-2 (CJB)
The Hebrew calendar is what’s known as a lunisolar calendar. This means that while the months are based on the lunar cycle, the year is synchronized with the solar cycle. The Christian holiday of Easter, which originated from Passover, still uses a lunisolar calendar to determine on which date it falls during the Gregorian year.