The Hebrew calendar is both solar and lunar, with twelve months. The lunar calendar is approximately eleven days shorter than twelve months, thus, every few years a leap month is added.
The day begins at sunset, the week begins on Saturday night, the month begins with the new moon, and the New Year, Rosh Hashanah, is in autumn.
There are twelve months in the Jewish calendar. The numbering of years is calculated from the creation of the world, which is traditionally understood to coincide with 3760 BCE.
The Hebrew calendar serves the religious and cultural purpose of keeping track of Holy Days, marriages, and the anniversaries of deaths. As a result of the discrepancy in days between the Jewish calendar year and the Gregorian calendar year, the date of each Holy Day will rotate each year. However, the difference from year to year is usually minor and each Holy Day can be expected to occur during the same season every year (e.g. Rosh Hashanah in the Fall, Pesach in the Spring, etc.)
The Jewish Sabbath begins at sundown on Friday evening and ends after sundown on Saturday evening.
Candles are lit, the kiddush, an ancient prayer over wine, is recited, and hallah (traditional bread) is served. Observant Jews go to synagogue Friday evening, Saturday morning, and Saturday evening.
All work is prohibited on Shabbat in order to commemorate G-d’s day of rest on the seventh day of creation as well as the Exodus from Egypt. It is a time for spiritual renewal, contemplation, learning, and family gathering.
Please note that on Shabbat, observant Jews do not work from Friday sundown to Saturday after sundown and that, as the days grow shorter in the winter months, early departure from school or work may be required.
In Jewish tradition, work includes a range of creative activities rather than simply physical or occupational labour. On Shabbat, observant Jews abstain from using technology, driving, writing, cooking, and commercial activities, among other tasks.
In the Bible, in addition to the Sabbath, the Holy Days are the three pilgrimage harvest festivals of Sukkot, Passover, and Shavuot; as well as the “Days of Awe,” the New Year and the Day of Atonement.
On all of these Holy Days, including the Sabbath (Saturdays), work is forbidden.
There are other post-biblical festivals on which work is permitted, such as Chanukah and Purim. In all cases, Holy Days are marked by special synagogue services and celebration in the home.