How does the Jewish calendar work?
The year
The Jewish calendar is a lunisolar calendar, meaning it is based on both the phases of the moon and the rhythm of the sun. The months are calculated according to the moon, so a Jewish month is 29 or 30 days long. Twelve months make up a year, which accordingly consists of 354 days, a difference of eleven days from the solar cycle.
To align the calendar with the solar year and to prevent holidays from shifting from one season to the next (many of them belong to a specific season), a leap month is inserted every two to three years, giving the year a total of 13 months. In a 19-year cycle, there are seven such leap years: every third, sixth, eighth, eleventh, fourteenth, seventeenth, and nineteenth year.
The counting of years in the Jewish calendar begins with the creation of the world. According to calculations based on the Torah, the creation of the world took place 3,761 years before the Christian calendar. To convert from the Christian year to the Jewish year, one must add 3,760 years. The year 2024 is therefore the year 5784 of the Jewish calendar. The year count is called 'AM' (Anno Mundi = in the year of the world).
The months
A Jewish month always begins with a new moon. Before a fixed calendar was introduced, the new moon had to be confirmed by two witnesses. Only then were all Jewish communities informed by fire signals or messengers, which could take longer depending on the distance. To ensure that major festivals were celebrated on the correct day, they lasted longer in more distant communities: the first day of the festival was celebrated twice.
The Jewish year begins on the first day of the 30-day month of Tishri (September-October), with the holiday of Rosh Hashanah (= head of the year). These months follow:
Heshvan (October – November) 29 or 30 days
Kislev (November – December) 30 or 29 days
Tevet (December – January) 29 days
Shvat (January – February) 30 days
Adar (February – March) 29 days
Nissan (March – April) 30 days
Ijjar (April – May) 29 days
Siwan (May – June) 30 days
Tammuz (June – July) 29 days
Aw (July – August) 30 days
Elul (August – September) 29 days
In leap years, a 30-day month is inserted between Shvat and Adar, called Adar I. The actual Adar becomes Adar II or Adar Sheni. All holidays and observances that fall in the month of Adar are celebrated in Adar II.
Weeks and days
The Jewish week has seven days, although the days do not have specific names but are numbered. The only exception is Shabbat, the weekly day of rest. According to the seven days in which God created the world, the week begins with Sunday and ends with Saturday (Shabbat), the holiest day of the week, dedicated to rest and spiritual renewal.
The days in the Jewish calendar do not begin at midnight, but at nightfall, and end at the same time the next day. Thus, Shabbat begins on Friday evening and ends at nightfall on Saturday. The same applies to all other days and holidays.
Important festivals and holidays
The Jewish calendar is rich in festivals and holidays that have both historical and religious significance. The most important are:
Rosh Hashanah : The Jewish New Year, celebrated at the beginning of the month of Tishri (September/October).
Yom Kippur : The Day of Atonement, ten days after Rosh Hashanah, is considered the holiest day of the year.
Sukkot : The Feast of Tabernacles is celebrated on the 15th of Tishri and commemorates the Exodus from Egypt.
Hanukkah : The Festival of Lights begins on the 25th of Kislev (November/December) and celebrates the rededication of the Temple in Jerusalem after the Maccabees' victory over the Seleucids.
Purim : A joyful festival commemorating the salvation of the Jewish people in ancient Persia. It is celebrated on the 14th of Adar (February/March).
Passover : Passover is celebrated on the 15th of Nissan (March/April). It commemorates the exodus of the Israelites from Egyptian slavery and the beginning of their journey to the Promised Land.
Shavuot : The Feast of Weeks Shavuot commemorates the giving of the Torah to the Jewish people at Mount Sinai, seven weeks after the Exodus from Egypt, i.e. on the 6th of Sivan (May/June).
You can find out when these holidays are celebrated according to the Gregorian calendar here:
https://de.chabad.org/holidays/default_cdo/jewish/holidays.htm