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
More than Rosh Hashanah is about the One Above, it is about us below.
He created the world. But we drive it to its destiny.
That is why it is called “the beginning of Your works”—even though it is not the anniversary of the creation of the universe, but of the human being. It is the true beginning, as all of time begins on this day.
Because on this day, more than any other, we are empowered to switch tracks, to transform our destiny and thereby the destiny of all of creation. Through us, the bitter darkness that shrouded truth and goodness can become a flaming torch of light.
All is defined by the destiny to which it leads. Even the past is redefined by the arrow of its future. The very existence of that time that held that past is re-created once it achieves its hidden destiny. A destiny that only you can reveal.
That is all that matters: What you do with your life right now.
Because today is the first day of your entire life, future and past.