calendar in common use throughout the western world is based on the
sun. Neither the year nor the months have anything to do with the phases
of the moon. The Muslims, on the other hand, reckon both the year and
the month according to the phases of the moon. Their year is therefore
shorter than the general year by about eleven days. A moon-year has
354 days, and a sun-year 365 days. The Jewish calendar is based on a
compromise between the two, and is reckoned according to both the sun
and the moon. The months are figured according to the moon (twelve months
of 29.5 days each), and the year according to the sun. In order to take
up the extra eleven days, a whole month is added to the calendar in
leap years. Every second or third year there is a thirteenth month,
a second Adar.
The Jewish calendar is a very old one. It has been established a long
time and every point and detail has been ironed out. But the history
of the calendar, how it evolved and how, in time, it came to be an established
fact, is very obscure.
It is to be presumed that in pre-historic times, when Jews were still
nomadic shepherd tribes in the wilderness, they reckoned time entirely
by the moon, as did all nomadic peoples. But it seems that after they
settled in Palestine and began to observe the agriculture seasons, they
also began to reckon according to the position of the sun. How the Jews
of the period equalized the sun-year and the moon-year we do not know.
It is possible that at one time they just added a number of days at
the end of each year. In time, however, the method of making every second
or third year a leap year was apparently established.
It appears that in the old days Jews figured their calendar - the month,
the year, and the festivals - entirely by observation, by testimony
offered that the moon had appeared and had been seen. Later, astronomic
calculation was instituted in connection with the calendar, but the
Jews were not certain of its exactness and still had recourse to witnesses.
The authority to hear this testimony and through it to establish the
beginning of the month, the intercalation of the calendar, and the dates
of the festivals was vested in the Sanhedrin.
When they accepted the report of the witnesses, the
New Moon was announced through the lighting of fires on the hill-tops.
Later, this method was not considered safe enough, and messengers were
sent out to proclaim the date. However, it took time for the messengers
of the Sanhedrin in Palestine to reach further lands inhabited by Jews
and proclaim there the arrival of the New Moon. It was, therefore, decreed
that outside of Palestine, in the lands of the Diaspora, festivals were
to be observed for two days instead of one. This added second day was
called "the second holiday of the Diaspora." An exception
was made in the case of Yom Kippur which, because of the hardship of
fasting, could not be prolonged. Rosh Hashanah was also an exception
in that it was observed for two days even in Palestine, for Rosh Hashanah
was also the New Moon, the first day of Tishrei. Even in Palestine it
could not always be ascertained on the preceding day whether the particular
day was the first day of Tishrei or the last day of Elul.
In later times the astronomical calculation of the calendar became so
precise that the practice of hearing witnesses was discarded, and the
Jewish calendar was established in every detail. Despite this, the observance
of the second day of festivals, known as the "second holiday of
the Diaspora," is still retained outside of Israel.
The Jewish Festivals: A Guide to Their History and Observance
(Schocken 1996, reprinted with the permission of the Union of American
of the Jewish calendar
Zodiac in the Jewish