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
The First Temple, why was it destroyed? Because of idolatry, murder and adultery.
The Second Temple, when they were occupied in studying Torah, doing mitzvahs, and acts of loving-kindness, why was it destroyed?
Because there were those who were intolerant of others without cause. Which teaches us that senseless intolerance is equal to idolatry, murder and adultery combined. (Talmud Yoma 9b.)
There is no sin of senseless intolerance listed in Torah. And yet, while the cardinal sins of Torah demanded only 70 years of exile, intolerance is so sinister, so powerful, it can take us almost two thousand years to heal from its wounds.
In simple terms, it’s much easier to deal with obvious, open failures and repair them. Intolerance, however, comes concealed beneath layers of justifications and self-righteousness. When you don’t believe you’ve done anything wrong, and on the contrary, that you were fighting a holy war, it’s hard to make up for all the damage caused.
Yet there is a deeper reason: Other sins, even the most heinous sins, are symptoms of flaws in the human person. To repair those flaws, each of us is granted 70 years upon this earth—ten years for each of the seven categories of emotions.
But intolerance of the other lies at the primal genesis of evil, at the point of fissure and subsequent fragmentation that occurred in the earliest stages of creation, as the universe lost contact with the infinite divine light that preceded it.
Because it is embedded so close to the core of our reality, it can attack the core of the human psyche, chochmah, the seminal point of reason.
That is why its antidote must also transcend reason. It must be related to the primordial infinite light itself, a light that knows no bounds. The key to healing humanity is therefore unreasonable.
Which means that with a single unpredictable and unconditional act of one human caring for another, connecting with another, especially another he feels he cannot tolerate, the whole of creation is healed and fulfilled.