One might expect the observance of Rosh Chodesh, the New Month, to take place when the moon is full; when its luminance is most pronounced. But Rosh Chodesh is celebrated at the new moon, when the moon's presence is essentially invisible in the dark, night sky. What is the lesson here? The Talmud tells us that Jews use a lunar calendar, while the nations of the world make use of the solar calendar. The reason says the S'fat Emet, is because the nations of the world can only function and exist when conditions are favorable... When their sun sets, so do their empires. Jews, on the other hand, live and exist even in darkness...