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The Hebrew Calendar


The Hebrew Calendar, unlike our Gregorian Calendar, is a calendar based on lunar phases.  Each new month in the Hebrew Calendar starts at the beginning of the lunar cycle, which is called “the new moon.”  The “new moon” is marked by the very first crescent of the moon to become visible in the sky after the conjunction of the earth, moon and sun.  So with the advent of “modern astronomy” with its super-telescopes coupled to high-speed supercomputers, some people think that they can improve on the Hebrew Calendar, how it’s computed, making it more accurate.  The Big Question is:  Have these people succeeded?   Secondly, and more important, we need to know whether the Hebrew Calendar and the way it is calculated, and has been calculated for thousands of years by the Jews, is God-ordained and God-authorized in the Bible.  If it is, and we can prove it, then we shouldn’t be tampering with it.  It’s just that simple.  Hopefully we’ll answer both questions in this short study.


Astronomical Conjunction verses Mean Conjunction


The Hebrew calendar does not attempt to calculate the astronomical conjunction, as does the Naval Observatory.

The astronomical conjunction occurs when the sun, moon and earth are on the same longitude.  i.e. the moon is directly between the earth and sun, so it is completely darkened out.

While the U.S. Naval Observatory uses detailed astronomical data to calculate the exact time of the astronomical conjunction (with the moon 100 percent darkened), the Hebrew calendar uses the average time of the conjunction, or the mean conjunction (see Maimonides, “Sanctification of the New Moon”, p.27)  i.e. The determination of the new moon of Tishri (7th month of the Hebrew calendar) is not based on the exact time of the conjunction, but on the average time of the conjunction, which rarely coincides with the actual conjunction.  The Hebrew term Molad means average or mean conjunction.  The purpose of calculating the Molad, or mean conjunction is to determine the earliest time that the new crescent may possibly be seen from Jerusalem.  If that time falls before noon Jerusalem time (JT), and the day is not contradicted by the Rules of Postponement, that day is declared the New Moon.  According to the Hebrew calendar, the New Moon of Tishri (7th month) is not the astronomical conjunction but the “new crescent.”  What I would say we need first of all is to find Scriptural evidence that this system utilizing the Molad was in use during Biblical times, giving it God-ordained authenticity.


Initial Scriptural Evidence


David and Jonathan knew when the New Moon would occur ahead of time, showing the Hebrew Calendar was already being calculated in advance of the actual occurrence of the New Moon.  The Hebrew word used for “new moon” is ghoh-desh (Strongs #2320).  It is first found in 1st Samuel 20:5, 18, “And David said to Jonathan, ‘Indeed tomorrow is the New Moon, and I should not fail to sit with the king to eat.  But let me go, that I may hide in the field until the third day at evening…Then Jonathan said to David, ‘Tomorrow is the New Moon; and you will be missed, because your seat will be empty.”  How did David know that the New Moon, the ghoh-desh would occur on the following day?  The first crescent occurs, at the very minimum, 17.2 hours after the astronomical conjunction, so it wouldn’t be visible to David one day before the actual first sighting of the crescent moon, which is the New Moon.  The only answer is that the New Moon had already been calculated out in advance!  Jonathan did not say “maybe” the New Moon, he said “tomorrow is the New Moon.”  They both knew that the Hebrew calendar had predicted the occurrence of the New Moon on the following day.  1st Samuel 20:24, “Then David hid in the field.  And when the New Moon had come, the king sat down on his seat to eat the feast.”  Also the Hebrew noun ghoh-desh (New Moon) is used with the Hebrew verb hay-yah (Strongs #1961), and translates to “was come.”  Hay-yah means to arise or appear, as also seen in Genesis 1:5 in reference to the appearance of the evening and the morning (sunset and sunrise) on the first day of creation.  The use of the verb hay-yah in 1st Samuel 20 reveals that when king Saul sat down to observe the Feast of Trumpets, the New Moon was clearly visible in the evening sky.  This is clearly evidence that the New Moon of Scripture is not the astronomical conjunction.  The astronomical conjunction takes place during “the dark of the moon”, and is not visible from any point on earth.  No part of the moon can appear in the sky during the astronomical conjunction.  Yet the verb hay-yah records the New Moon appeared in the sky above the palace of Saul and above the field where David was hiding.  That day, which had been calculated in advance, was confirmed by the appearance of the New Moon.


The New Moon of Modern Astronomy is not the New Moon of Scripture


The astronomical conjunction does not determine the appointed times of God (i.e. the calculations for the beginning of each month, when Passover falls for the 14th Nisan, and the 1st of Tishri when the Feast of Trumpets falls).  On modern calendars the astronomical conjunction of the moon, earth and sun is designated as the “new moon.”  Because the conjunction takes place during the “dark of the moon,” the “new moon” is depicted as a black circle in the modern Gregorian calendars.  But the “new moon” of modern astronomy is not the new moon of Scripture.  The astronomical conjunction does not determine the appointed times of God.  What determines the appointed times of is the earliest possible visibility of the new crescent of the moon as calculated on the Hebrew calendar.  A minimum of 17.2 hours must pass from the time of the astronomical conjunction before the crescent can possibly be seen by the naked eye.  Naval Observatory astronomical conjunctions will always differ from those of the Hebrew calendar.  Why?  Rather than calculate the astronomical conjunction the Hebrew calendar uses the mean conjunction to project the earliest visible crescent. 


Why use the mean conjunction to calculate the new moons?


The “mean conjunction” provides a consistent basis for the calculation of the new moon of Tishri 1 from year to year.  Tishri 1 is always used to set up the next year’s calendar, and not Nisan 1 (we’ll get into that later).  But why use the “mean conjunction”?  This is why.  The actual time from one astronomical conjunction to another---from one month to another---fluctuates from five minutes to three hours, and may vary more than twelve hours in the course of the year.  “To calculate the exact time of conjunction for each and every month for a whole year would require double-precision (64-bit) arithmetic”  (Dershowitz and Reingold, The Calendrical Calculations, p. 135).  The Hebrew calendar resolves the problem by using the average or mean time---that is, 29.5 days for the length of its months (alternating between 29 and 30 days every other month).  The variation in length of time between astronomical conjunctions is caused by the countless irregularities that occur in the moon’s orbit.  To date, astronomers have identified more than 5,000 perturbations of the moon as it circles the earth.  Before modern astronomy with its computerized mathematics, it would have been an impossible task to calculate the exact astronomical conjunctions from month to month and year to year, and then calculate on that basis the day of the new moon (i.e. when the first crescent appears).  That is why God established the mean conjunction as the basis for calculating the New Moon. The use of that mean conjunction provides a simple, reliable and consistent basis for calculation in the Hebrew calendar. 


Determining the New Moon Day


In the days of David and the early kings of Israel the lunar cycle was much more constant.  During the reigns of Ahaz and later in Hezekiah’s reign God directly altered the arrangement of the heavenly bodies (within the solar system, sun, moon, etc.).  Those changes required new steps to be added to the process of determining the New Moon.  Among the procedures that were instituted to adjust the Hebrew calendar to the changes in the heavenly bodies are what are called “The Rules of Postponement.”  Some claim these Rules of Postponement postpone the observation of Tishri 1 past the time of the New Moon.  But they do no such thing.  Instead, they keep the observation of Tishri 1 “in harmony” with the cycle of the heavenly bodies.  In as many as six years out of ten, these rules must be applied in order to ensure that the declaration of Tishri 1 is as accurate as possible.


Evidence the Rules of Postponement Were Being Followed in the time of Ezra and Nehemiah


In two separate instances (Ezra 3:1-6; 6:1-22) during the time of Ezra, knowing the exact day Tishri 1 was observed and kept, and by comparing data from very accurate Hebrew calendar software programmed to John Kossey’s “The Hebrew Calendar: A Mathematical Introduction” proves the Rules of Postponement were being employed by Ezra, and also that these “Rules of Postponement” were adjusting the declaration of Tishri 1 to the actual time when the crescent of the New Moon would become visible (astronomically from Jerusalem).  The second passage in Ezra shows the declaration of the New Moon accurately using the Rules of Postponement for the 5th month on the Hebrew calendar through programmed calculations using Kossey’s “The Hebrew Calendar: A Mathematical Introduction.” 


The Sanhedrin in charge of Calendrical calculations


During the time of Christ the Nasi or President of the Sanhedrin was in charge of the calculations for the Hebrew Calendar.  The Nasi or President of the Sanhedrin had a lineage going back to Ezra, who then goes back to Hilkiah the high priest who was the father of Jeremiah the Prophet.  They had all inherited a full knowledge of the Hebrew calendar, including intercalculations and the Rules of Postponement.  These nasi’s ruled, right after the time of Christ, outside of Jerusalem up to Hillel II in the 300s AD.  So we see the regulation of the Hebrew Calendar by a central authority and single family going from the 300s AD back to Ezra, and then back to Hilkiah the high priest and father of Jeremiah the Prophet!  Anyone who says Hillel II invented the Rules of Postponement is going directly against the records of history, both in the Bible and those histories accurately maintained by the Jews themselves.  Hillel II, as the last of the great sages, used his office of nasi to absolutely guarantee that the knowledge of the Hebrew Calendar and its methods of calculation would not be lost.  He made sure this priestly knowledge---withheld from the general populace until his day---was imparted worldwide to all the Jews.  Why?  He was worried that continued Roman persecution might do away with the observance of the Holy Days at the proper times commanded by God in his Word.  The New Moons of Nisan 1 and Tishri 1 were determined far in advance, and were only verified by direct observation.  The discussion of the ancient rabbis in the tractate Rosh Hashanah offers historical evidence that the Hebrew Calendar at the time of Christ and the apostle Paul was both calculated and intercalculated when the bet din calculated the calendar for the upcoming year.  The most important part of their work was determining the New Moon of Tishri, which would set the Holy Day season for the entire upcoming year.  Included in their calculations was the application of rules, whether written or not, which called for the intercalculation in a set pattern of years (3, 6, 8, 11, 14, 17, 19) [in a 19-year time cycle---which would then be repeated for the next 19-year time cycle, and so forth].  The addition of a 13th month in these years (3, 6, 8, 11, 14, 17, 19) automatically made Tishri 1, and all the Holy Days, fall a month later in the solar year, keeping these days in harmony with the harvest seasons.  The calendar was further adjusted by applying the Rules of Postponement, which delayed the declaration of the New Moon of Tishri by one or two days.  This “fine tuning” of the calendar kept the months of the year aligned with the lunar cycle.  The calculation of the New Moon and the practice of intercalculation did not begin at the time of Hillel II, as some have claimed.  The records of the Jerusalem Talmud clearly contradict this assertion.  The historical evidence in the tractate Rosh Hashanah confirms that the calculated Hebrew calendar was in effect at the time of Christ and Paul---more than 300 years before Hillel II, who merely codified the rules.


Rules of Postponement


1.  The Feast of Trumpets, Rosh Hashanah, Tishri 1, may not occur on Sunday, Wednesday, or Friday.  If Rosh Hashanah were on Sunday, Hosha’na Rabbah (the 7th day of the Feast of Tabernacles) would be on Saturday, and this must be avoided because it would prevent the proper celebration of the Festival of Willows.  If Rosh Hashanah were on Wednesday, Yom Kippur would be on a Friday and this would cause undue hardship because there would be two days in a row with severe restrictions.  If Rosh Hashanah were on a Friday, Yom Kippur would be on a Sunday, and, again, we would have two days in a row with severe restrictions.  Therefore, if the new moon (Molad) is on either Sunday, Wednesday or Friday, the first day of Tishri (7th month) is postponed to the following day.


2.  If the New Moon (Molad) of Tishri occurs at noon or later, the New Moon (Rosh Hodesh) is declared to be the following day.  Thus, if the Molad (new moon) is Monday at noon or later, Tuesday is declared to be Rosh Hodesh (New Moon).  The reason is that if the Molad (new moon) is before noon, it is certain that the new crescent will be visible in some part of the world before sunset of the same day.  If however, the new moon (Molad) occurs after midday, the new crescent will not be visible before sunset of the same day [which makes it the beginning of the next day].  If the following day is Sunday, Wednesday, or Friday [employing rule #1] on which the first day of Tishri may not occur, it is further postponed to the next following day, so that the first of Tishri is the third day counting from, and including, the day of the Molad (new moon).


3.  If the Molad of Tishri in an ordinary year is on Tuesday at 3:204/1080 A.M. or later, the first of Tishri is postponed to Thursday.  It cannot be on Tuesday because then the next year’s New Moon (Molad) of Tishri would be on Saturday afternoon and new moon (Rosh Hodesh) would have to be postponed to Sunday.  This would make the year in question 356 days long, which is more than the statutory limit of 355 days.


4.  This occurs if the New Moon (Molad) of Tishri, in a year succeeding a leap year, is on a Monday after 9:00 A.M. (ie. The fifteenth hour from the beginning of the night before) and 589/1080 parts.  If this year were to begin on Monday, Rosh Hashanah of the preceding year would have fallen on Tuesday noon, and would have been postponed to Wednesday.  This would make the current year 382 days in length, which is lower than the statutory limit of 383 days.  [statutory limit, that is, for a leap year containing one extra month.]


I know most of those rules seem real complicated.  It’s just important to understand that they were designed as a system to “fine tune” the  calculated calendar so it would always stay in harmony with both the seasons and the actual spotting of the new moon, the first crescent, as it appears in the sky a minimum of 17.2 hours after the Molad or mean conjunction of earth, sun and moon.  We don’t have to know how to use them to calculate our own calendar, the Jews do a good and accurate enough job of that.  We’ll see just how accurate a job they do in a little while.


The Abib, Season of the Ripening Ears


Some have rejected the intercalary rules of the Hebrew calendar.  They claim that it is no longer necessary for the months of the year to coincide with the harvest cycle [in Palestine].  Because the Wave Sheaf is no longer offered [it was being offered all the way up to 70AD], they see no reason to wait for the ripening of the first barley [sheaf] before the beginning of the new year.  Those who hold this view are ignoring the fact that when God linked the year to the harvest cycle, he did not make any reference to the offering of the Wave Sheaf.  God’s instructions were only to observe the Passover and Days of Unleavened Bread in the first month.  This month is clearly identified in Scripture as the time of the ripening of barley, although the offering of the Wave Sheaf did not begin until 40 years later---after the children of Israel had entered the Promised Land.


God gave Moses the timing, when the first day of the first month was to begin


The book of Exodus records that the knowledge of when to begin the new year was spoken directly to Moses, who delivered it to the elders of the tribes of Israel.  Exodus 12:1-3a, “And the LORD spake unto Moses and Aaron in the land of Egypt, saying, This month shall be unto you the beginning of months:  it shall be the first month of the year.  Speak ye unto all the congregation of Israel, saying, In the tenth day of this month they shall take to them every man a lamb,…”  How would they have known the tenth day, unless God had directly revealed the very first day of the first month to Moses.  Verses 1-2 are not a general statement, but a revealing of the exact timing for the beginning of the first day of the first month.  Abib is not the title of the month but a descriptive term linking the first month with the beginning of the spring harvest cycle, abib meaning “green ears.”  God told Moses exactly when the first day of the first month began.  Each new month began at the new moon (at the first appearance of the crescent moon).  Since a major Holy Day started on the first day of the seventh month, Tishri 1, the Aaronic/Levitical priesthood from Aaron and his sons on out used Tishri 1 for the calculating of the Hebrew Calendar, with its Holy Days.  The use of the word abib in the Hebrew text of Exodus makes it clear that the beginning of the Hebrew year hinges on the state of the barley harvest.  There is no evidence in Scripture to support the claim that God’s command for beginning the year with the Abib no longer applies.  To the contrary, the Scriptures clearly command that the festivals of God in the first month of the year be observed “in season” (read Leviticus 23:4; Numbers 9: 1-3).  The new moon of the first month is not a festival, or annual Sabbath, as the New Moon of the seventh month.  The New Moon of the seventh month is the only new moon of the year that has been sanctified by God as a Holy Day.  There is no Scriptural basis for observing the new moon of the first month.  Neither is there any Scriptural basis for calculating the other months of the year from the first month.  The Scriptures reveal that God ordained the New Moon of the seventh month as the basis for calculating the New Year.  Psalm 81:3-5, “Blow up the trumpet in the new moon, in the time appointed, on our solemn feast day.  For this was a statute for Israel, and a law of the God of Jacob.  This he ordained in Joseph for a testimony, when he went out through the land of Egypt:  where I heard language that I understood not” (KJV).  When we understand the meaning of the Hebrew words, it is evident that at the time of the Exodus from Egypt, God issued Moses and Aaron “a law of a festival” ghohk.  The festival for which this law was issued was the New Moon of the seventh month.  This law decreed that each year the New Moon of the seventh month was to be presented for judgment by computation, and that a written prescription, or calendar, was to be issued.  The record we find in Psalm 81:3-5 reveals that God wrote the initial “calendar prescription” by computing the calendar for Israel at the time they left Egypt.  It was decreed by God that the molad of the seventh month be calculated year by year.  The Hebrew text clearly contradicts those who claim that the new moon of the first month should determine the appointed times of God (cf. Psalm 81:3-5).  The New Moon of the seventh month is the new moon that God ordained to set the months of the year.  Those who use the new moon of the first month are violating the clear decree of God himself as recorded in Psalm 81.


U.S. Naval Observatory Data verses the Hebrew Calendar


Does the use of observatory data lead to more accurate results than the Jewish calculations for the Hebrew Calendar?  The U.S. Naval Observatory calculated the astronomical conjunction of Nisan 1 in the year 2000 to occur at 20:13 JT (10:13 PM) on Tuesday, April 4.  Since the conjunction falls after sunset, this figure would place Nisan 1 on Wednesday, April 5, and Nisan 15 on Wednesday, April 19.  The new moon on the eve of Wednesday, April 5, will not be visible because the conjunction will occur at 10:13 PM that evening.  A minimum of 17.2 hours must pass from the time of the conjunction [black of the moon] before the new crescent can possibly be seen.  The full moon on the eve of April 19, which by this reckoning would be Nisan 15, the first day of the Feast of Unleavened Bread, will be a perfect100 %, indicating that the declaration was on target.  However, the full moon on the eve of Tishri 15, which by this reckoning would be Thursday, October 12, will be only 96% accuracy for the two dates.


How do the calculations of the Hebrew Calendar compare?


The Hebrew Calendar places Nisan 1 on Thursday, April 6, and Nisan 15 on Thursday, April 20.  The new moon on the eve of Thursday, April 6, will be visible over Jerusalem for a little less than one hour after sunset.  The crescent will be visible because almost 20 hours will have passed since the conjunction the evening before.  The full moon on the eve of Nisan 15 will be 99%, which is 1% less than the date set by the observatory reckoning.  However, the full moon on the eve of Tishri 15, which by Hebrew Calendar rules falls on Sunday, October 14, will be a perfect 100%.  Thus the Hebrew Calendar achieves an average of 99.5% accuracy for the two dates.  The calculations of the Hebrew Calendar for the months of Nisan and Tishri are more accurately aligned with the phases of the moon than are the dates that are calculated by observatory data.  No astronomical tables were consulted to validate the dates for these festivals.  After thousands of years of festival dates have been calculated, why do some assume that there is a need to improve the calculations of the Hebrew Calendar? 


New Testament Scriptural Evidence


Much of the New Testament chronology centers around the declarations of the holy days of God, which Jesus observed.  Should we now attempt to invalidate the observances that are documented in the Gospel accounts, when Jesus himself sanctioned these declarations by his own example?  Look up for yourself all the places where Jesus went to the Feasts, both Passover and Tabernacles, throughout his 3.5 year ministry.  These Holy Days were calculated by the acting Sanhedrin to formulate the Hebrew Calendar year by year for the entire lifetime of Jesus, from childhood to his crucifixion.  Then 50 days after this last Passover, the disciples of Jesus were observing the Day of Pentecost, Shevuot, on the same day the Jews in Jerusalem were, in the very Temple of God!  Again, why do some assume that there is a need to improve the Hebrew Calendar?  Such action would show arrogant disregard for the inspiration of Scripture and the Lordship of Jesus Christ.  The Postponement Rules and mathematical constants of the Hebrew Calendar supersede all the astronomical calculations that may be obtained from an observatory, almanac, or other source of lunar information.  None of these sources had any bearing on the declarations of the feasts of God.  The Hebrew Calendar does not now nor has it ever defined the Molad of Tishri as the time of the astronomical conjunction.  The two calculations are not aimed at defining the same event.  Determining the exact time of the moon’s conjunction is not part of the calculations for the dates of the feast days.  Astronomical data cannot improve on the accuracy of the Hebrew Calendar.  All attempts to forge a better calendar by the infusion of mounds of information have demonstrated that, while it is not possible to construct a perfect relationship between lunar phases and God’s feast days, the Hebrew Calendar is, nonetheless, the best calendar possible. 


Mathematical Evidence


Plain mathematical evidence exists to show that the calculations of the Hebrew Calendar are aimed at mid-course corrections based on an average, which reduces the potential for errors.  The Hebrew Calendar avoids specific readings of the moon’s position at a finite point in time.  The results of using the average or mean lunar period and applying the four Rules of Postponement will demonstrate that this method is much more accurate than calculations that are based on specific astronomical data.  The figures speak for themselves.  Since postponements are applicable 61% of the years, gross miscalculations would occur if these rules were not valid.  A comparison of the calculated Hebrew Calendar with calendars that are based on the moment of the darkest moon or the observation of the new crescent will demonstrate that through the years, the Hebrew Calendar achieves the highest percentage of accuracy in matching day of the month to the desired lunar phase.  This degree of success would not be possible without the Rules of Postponement and the use of the average lunar month (29.53 days) for calculations.  The increased availability of astronomical data that is offered by our modern hi-tech computer age cannot improve the accuracy of the lunar dates that are calculated by the Hebrew Calendar.


This year’s Hebrew Calendar


To see an up-to-date Hebrew Calendar side by side with the Gregorian (astronomical) Calendar, log onto:



Most of the text for this booklet has been directly excerpted from “The Feast of Trumpets 2000 AD” by Dwight Blevins & Carl D. Franklin, Christian Biblical Church of God, P.O. Box 1442, Hollister, CA  95024-1442.  For a more in-depth treatment of this subject, be sure to write to the above address and request a free copy of their booklet “The Feast of Trumpets 2000 AD” for yourself. 

Copyright © 2010, Christian Biblical Church of God, all rights reserved.


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