The last Sabbath of each Hebrew month, like today, is called Shabbat Mevarchim HaChodesh, or the Sabbath which blesses the month.
So today liturgically-observant Jews said the special prayer which asks God to "renew it [the coming new month] . . . for life and for peace, for gladness and for joy, for deliverance and for consolation."
And tonight already is Rosh Chodesh, the first of the month of Nissan.
In fact, it began at exactly 9:34:23 p.m.
How do we know? Well, the Hebrew calendar revolves around the moon, so to speak.
Each month represents one lunar cycle, the time it takes the moon to make one orbit around the earth.
There is a point when the moon is exactly between the earth and the sun, and so, hidden to anyone here on earth.
The molad is the time of the moon’s "birth," when it emerges just enough that a thin crescent of its illuminated surface can first be observed from Jerusalem.
This exact moment signals the beginning of a new Jewish month.
(This photo is just for illustration of a "banana moon."
It actually shows a rare phenomenon called the occultation of Venus which occurred last June 18. But that’s a different story!)
Wishing you chodesh tov and shavua tov, a good month and a good week.