More than 3,000 years ago, G-d commanded the Jews, then slaves in Egypt, to proclaim the holiness of the month of Nisan.  Since that first mitzvah, the first collective act of Jewish nationhood, the lunar-determined calendar has guided the Jewish People throughout its history.

During the times of the First and Second Temples, the Sanhedrin (Great Assembly) certified witnesses of the New Moon and sanctified each New Month (Rosh Chodesh) which they announce through a network of hilltop fires and messengers.  

In the 4th century C.E., Hillel II set all future Jewish months and years in an order of time that endures until this day, universally accepted in Israel and the Diaspora.

The lunar year contains 354 days, eleven days less thatn the solar year. Since the Torah requires holidays to occur within specific seasons, it is necessary to add a 13th month to the Jewish Calendar ot gu9arantee that Passover is always celebrated in the Spring.  This extra month, Adar I, is added tseven times over a nineteen year span.

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