**Molad** (plural

*Moladot*) is a

Hebrew word meaning "birth" that also
generically refers to the time at which the New Moon is "born". The
word is ambiguous, however, because depending on the context it
could refer to the

**actual** or

**mean**
astronomical lunar conjunction (calculated by a specified method,
for a specified time zone), or the

*molad* of the
traditional Hebrew calendar (or another specified calendar), or at
a specified locale the first visibility of the new lunar crescent
after a lunar conjunction.

*Molad Emtzai* (Average *Molad*)

The
**molad emtzai** (average *molad*,
used for the traditional Hebrew calendar) is based on a constant
interval cycle that is widely but incorrectly regarded as an
approximation of the time in Jerusalem of the mean lunar conjunction. Each

*molad* moment occurs exactly 29 days 12 hours 44 minutes
and 3+

^{1}/

_{3} seconds after the previous

*molad* moment. This interval is numerically exactly the
same as the length of the mean synodic month that was published by

Ptolemy in the

Almagest. Although this interval quite closely
approximates the average time between lunar

conjunctions, in the present era it
is about

^{3}/

_{5} second too long.

The traditional

epoch of the
cycle was 5 hours 11 minutes and 20 seconds after the

**mean
sunset** (considered to be 6 hours before midnight) at the
epoch of the Hebrew calendar (first eve of

*Tishrei* of
Hebrew year 1).

Historically, the original *molad*
reference meridian of longitude was halfway between the Nile river and the end of the Euphrates river, but the excess length of the
*molad* interval causes it to drift progressively eastward
at an accelerating rate — in the present era it is at a meridian
that passes near Qandahar,
Afghanistan!
Although the moment of the traditional Hebrew calendar

*molad* is announced in

synagogues
on the

*Shabbat* prior to each month
(except before

*Tishrei*), its only
relevance to the present day fixed arithmetic

lunisolar Hebrew
calendar is that the

*molad* of the month of

*Tishrei* determines the date of the
New Year Day (

*Rosh Hashanah*),
subject to possible postponements of 0, 1 or 2 days (depending on
certain postponement rules).

Traditionally the announced or printed

*molad* moment is
quoted in terms of the hours, minutes, and 18

^{ths} of a
minute elapsed from mean sunset, because

Hebrew calendar days begin at sunset. Some
printed sources subtract 6 hours to convert the

*molad*
moment to "civil" time, but doing so causes the Hebrew weekday to
be wrong 25% of the time (whenever the

*molad* moment is
between sunset and midnight). Also, some printed sources even add
an hour during the summertime for "daylight saving", but that is
also a mistake because that would affect the

*molad* of

*Tishrei* and occasionally imply an
erroneous date for

*Rosh
Hashanah*.

*Molad Amiti* (True *Molad*)

The
**molad amiti** (true *molad*), which
has no relevance to the Hebrew calendar, is the time at which the
actual astronomical lunar
conjunction occurs, often expressed either as the mean solar
time in Jerusalem (Universal Time + 2h
20m 56s or simply + 2h 21m) or as the clock time in Israel. If
the moment is desired for ritual or social purposes then it may be
best to express it in terms of the local clock time.

On average the traditional

*molad* of the Hebrew calendar is
currently >2 hours late, and there are substantial periodic
variations in the astronomical lunar cycle length, such that in the
present era it varies over a 28-hour span ranging from 12 hours
early to 16 hours late, compared to the Jerusalem mean solar time

*molad amiti*, if all months are included in the evaluation.
If the evaluation is limited to a single Hebrew month, however, for
example

*Tishrei*, then the portion of the variations that
are due to Earth orbital eccentricity are for the most part
eliminated and the average has an offset that is month-specific,
such that presently the

*molad* of

*Tishrei* varies
over about a 20-hour span ranging from 4 hours early to 16 hours
late.

## See also

## External links