Shortly before sundown on the 29th of Adar, G-d commanded Moses regarding the mitzvah of sanctifying the crescent new moon and establishing a lunar calendar. This is the first mitzvah the Jews were given as a nation.
Moses had difficulty envisaging the moon's appearance at the exact moment of its monthly rebirth. After the sun set, G-d showed Moses the crescent new moon of the new month of Nissan, showing him the precise dimensions of the moon at the moment the new month is to be consecrated.
For the generations that followed, each new month was ushered in when two witnesses testified before the Sanhedrin (rabbinic supreme court) that they had seen the molad, the new moon. In the 4th century CE, Hillel II foresaw that the Jews would no longer be able to follow a Sanhedrin-based calendar. So Hillel and his rabbinical court established the perpetual calendar which is followed today -- until Moshiach will come and reestablish the Sanhedrin.
Links::
Lunar Time
Rosh Chodesh
The Molad
A few months after its creation, Napoleon's "Sanhedrin" (rabbinical supreme court) was dissolved. The Sanhedrin was created to approve certain religious regulations requested by the French "Assembly of Notables." The regulations were designed to blur the distinction between Jews and non-Jews.
The rulings of this pseudo-Sanhedrin were never adopted by Jewish communities.
Link:: Napoleon Bonoparte
Every year, our sages taught, with the cry of the shofar, the entire universe is reborn.
And so, at that time, with our resolutions and our prayers, we hold an awesome power: To determine what sort of child this newborn year shall be—how it will take its first breaths, how it will struggle to its feet, and how it will carry us through life for the twelve months to come.
In truth, it is not only once a year. At every new moon, in a smaller way, all life is renewed again.
And so too, every morning, we are all reborn from a nighttime taste of death.
And at every moment—in the smallest increment of time—every particle of the universe is projected into being out of absolute nothingness, as it was at the very beginning.
Which is why there is always hope. Because at every moment, life is born anew. And we are the masters of how this new moment will be born.