Calendar Vocabulary
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1 part (halek  or chalyek)


76 moments (reaim)

A part consists of 76 moments.

1 hour


1080 parts (halakim or chalakim)

The hour consists of 1080 parts or halakim or chalakim. Each halek is equal to 3 1/3 seconds. Use of parts or halakim has the advantage of eliminating fractions. We will use the English word parts for simplicity.

1 day


24 hours

Genesis 1:5 shows that a day begins in the evening. While a new day begins with the setting of the sun, 6 p.m. is the arbitrary start of a new day e.g., Monday starts on Sunday 6 p.m. This moment is called Monday 0 h in the Jewish calendar. At John 11:9 Jesus refers to the daytime consisting of 12 hours.

1 week


7 days


1 mean synodic month


29 days 12 hours 793 parts

A lunar month is the time needed for the moon to revolve around the earth. As this period, called a lunation, varies from month-to-month, a mean synodic month of 29 days 12 hours 793 parts, or 44 minutes 3 1/3 seconds, is the traditional average used for calculation. Actual calendars cannot be based upon 29 days so the Hebrew Calendar incorporates months of 29 and 30 days.

start of new year


  The year starts with the moment of the mean molad (mean conjunction, mean astronomical New Moon) of the month of Tishri (Frank1956:14).

1 common year


12 lunar months

A common year will have 353, 354, or 355 days.

1 intercalary year


13 lunar months

An intercalary year, also called an embolismic year or leap year,  will have an extra month of 30 days. Leap years may have 383, 384, or 385 days.

1 nineteen year cycle


235 lunar months, or 12 common years and 7 intercalary years

Every 19 solar years (of some 365 days), the moon has revolved around the earth 235 times. Each lunation being on the average of 29 days 12 hours 793 parts. This is also known as the cycle of Meton or Metonic cycle. This astronomical relationship makes it possible to combine common years and leap years together in a fundamental pattern which repeats itself every nineteen years. Nevertheless, you should be aware that 235 lunar months is about an 1 hours less than 19 Julian years. To be precise, 235 lunations is 1 hour 485 parts less than 19 Julian years.




The computed time for the conjunction of the sun, moon, and the earth is a molad, from the Hebrew molad (plural, moledoth). The word means rejuvenation or renewal.

Molad Tohu



The time of the mean molad at the beginning of its year 1, 2nd day (Monday) 5 hours after the beginning of Monday (reckoning days in Hebrew time beginning at 6 p.m.), which is Sunday 11 p.m. or 23 h 204 p. Sunday. In Jewish tradition "This moment would fall almost 12 months before Creation and is, therefore, proleptic, a chronological fiction....and only its final 5 days and 14 hours were after creation" (Frank 1956:15).

The bench mark (the Molad of Tishri) for the year 3761 BCE


1 day 23 hours 204 parts (Sunday, October 6 on the Julian Calendar)

Tishri is the seventh month on the sacred calendar and the first month of the civil calendar. The Molad of Tishri is the computed time of the new moon of the month of Tishri.

Any known molad expressed as day of the month, day of the week, hours, and parts, e.g., October 6, Sunday, 23 h 204 p in 3761 BCE (reckoning days in Roman time beginning at midnight), can serve as bench mark. For ease in calculation the most practical choice for a bench mark is the Molad of Tishri of year one in a 19-year cycle. 

molad advancement


  A molad advances with respect to a known molad because of the excess time in one average lunar month over a full number of weeks.

Leap Years in the present-day Jewish Calendar (New Cycle)


Year 3, 6, 8, 11, 14, 17, and 19 in a nineteen year cycle

A difference of 6 minutes 39.371 seconds in the Hebrew calendar's solar year and the true astronomical value causes Passover to occur one day later every 216 years. This eventually would place Pentecost in the beginning of summer. This violates the rule that Pentecost must be in the spring necessitating a postponement, by one year, of the intercalary months on or after 257 CE.

Leap Years in the time of Moses through the Apostolic Age (Old Cycle)


Year 2, 5, 7, 10, 13, 16, and 18 in a nineteen year cycle

Computer calendar programs which do not take into account the one year postponement in the leap years provide incorrect dates.

Leap Years in the time of the Patriarchs (Patriarchal Cycle)


Year 1, 4, 6, 9, 12, 15, and 17 in a nineteen year cycle

The rule that Pentecost can only occur in the spring also requires that a postponement, by one year, of the intercalary months had to have occurred in patriarchal times. The phenomenon occurs about every two thousand years.

elapsed time


  The excess over full weeks from the bench mark to the molad of the required year. The total molad advancement is simply the excess over the number of full weeks in the elapsed time from the bench mark to the molad Tishri of the desired Roman year.



Seder Olam




Anno Mundi



Page last edited: 04/06/06 09:18 PM

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