אלה מועדי ה" מקראי קדש אשר תקראו אתם במועדם

Judaism uses the Hebrew calendar for all the religious matters, feasts and anniversaries. It is the Israeli official calendar, although the Gregorian calendar is in use for all the secular domains.

The Jewish calendar is based on both the cycles of the moon and of the seasons, in order to observe the solemnities of the Torah.

In the ancient times, a few people appointed by the Rabbis in Jerusalem would testify having seen the new moon, and then the Sanhedrin (rabbinical court) would sanctify the new month^[xxxiii]. It took some time then to propagate the news to the neighbouring cities and further to the extent of the whole Jewish population. If the next month to be sanctified was Nissan, and the signs of the sprint season could not be seen yet in the fields, an additional month was then inserted ^[xlvii], in order to observe the feast of Pesach in the spring^[xxxi].

Later, after the fall of Jerusalem by the Roman empire, and because of the threat of dissolution of the Sanhedrin, Rabbi Hillel son of Yehuda Hanassi, who was presiding the Sanhedrin, established the calculation rules of the calendar in year 358 of the common era in order to facilitate its observance accross the world.

This site presents the features of the Jewish calendar, the natural and astronomical phenomena that rule on it, and the religious events whose basis it is. Also I propose a perpetual calculation method and a few tools for translating Jewish dates into secular and vice versa.