The Biblical Calendar and the Hebrew Calendar



The word “calendar” comes from the Latin terms “calendae” and “calendarium”.

 A “calendarium” was the book that epitomized the astronomical, agricultural and religious events of the month, indicating the number of its days, the length of days and nights, the various festivals and the constellation crossed by the Sun.

  The Latin word “calendae”, which derives from the verb “calare”, comes from the Greek καλεῖν: kalein, which means to “call” or “summon”. The name comes from the fact that on the first day (calendae) of each month, the community was summoned to participate in the monthly games and festivities. This summon that was not a Greek tradition but an exclusively Roman practice, is the source of the Roman adage “ad calenda graecas” or up “to the Greek summoning”, which means “never”, and is still applied to the remote end of a lengthy issue.

  The astronomical calendar provides the fundamental units of the measurement of time, and is based on the observation of the Sun, the Moon, and of some stars, as it was established by the Creator when he said: “Let the luminaries appear through the expansion of heaven, in order to divide day and night, and be a sign for the seasons, the days and the years”. (Genesis 1:14)

  There are since old times, different types of calendars; the lunar calendar based on the synodic cycle of the moon, the solar calendar based on the tropic cycle of the sun, and the so called lunisolar calendar, which integrates and synchronizes both cycles.


The synodic or moon cycle

  The synodic cycle covers the rotation period of the Moon around the planet, till it recovers its aligned position with the Sun and the Earth; this period can be defined as the time elapsed after a new moon and the next.

The complete cycle is divided into four phases, each comprising almost a week, really, about 7.38265 days. These four phases involve precisely the 29.5305888531 days of the lunar month and imply the full cycle of the synodic rotation.

(The word synodic comes from the Latin synodicum and from Greek Συνοδικός or synodikos, which mean gathering or conjunction).


The tropic or Sun cycle

  The tropic cycle or solar year includes the period between two successive transits of the Sun over the Zenith of the same tropic (see Annex), that is, between two solstices and two equinoxes of the same name. This period corresponds to the Earth's rotation around the Sun.

  The length of the tropic year is not constant; the reason is that the precession of the equinoxes, similar to the motion of a spinning top, causes variations on the orientation of the rotation axis of the Earth, shifting gradually the point zero. This led to the fixing of an average tropic year equal to 365.24218967 days, that is: 365 days, 5 hours, 48 minutes and 45.98 seconds.

(Tropic: from the Greek τροπικός: tropikόs, meaning rotation)


a)   A solar year does not correspond to a precise number of lunar months; this fact gave rise to different calendars for the solar and lunar cycles. Some of the calendars based on the tropic or solar cycle are: the ancient Egyptian calendar, the Julian calendar and the current Gregorian calendar, largely used around the world.


b)   The lunar calendar begins its months with the new moon's day. Two of the calendars based on the synodic or moon cycle are: the Bible calendar and the current Islamic calendar.


c)   The lunisolar system synchronizes the solar and lunar calendars, by alternating the 12 month years with some 13 month years, in accordance with the Metonic cycle (Greek: Μέτωνος κύκλος).

Some lunisolar calendars are: the ancient Assyrian-Babylonian and Hebrew calendars, and the current Hebrew calendar.


The Bible calendar

  In the book of Shemot, also called Exodus, Yahuh God tells Moses and Aaron: “This month shall be for you the head of the months, the first month of the year”. (Exodus 12:2) Therefore, the biblical calendar is that given by God to the people of Israel.

  The Mekilta, a work of Rabbi Yisma'el Merita (2nd century AD), contains the rules for the interpretation and exegesis of the Book of Exodus, and in a note on Exodus 12:2, says: “The nations do their counting with the Sun, but Israel, with the Moon”. And Psalm 104:19 also states: “God made the moon to calculate the time”.

  The Israelites used the lunar calendar until their exile in Babylon, and then adopted a lunisolar calendar derived from the Babylonian, which is the official calendar in the state of Israel.


The Hebrew Calendar (הלוח העברי, Ha-lu'ach ha-ibri)

  The Hebrew calendar is as stated, a lunisolar calendar derived from that of the Assyrian-Babylonians.

  Now, the difference between the twelve lunar month cycle and the solar year is approximately of 10 days and 21 hours; to compensate for this difference, the intercalation of a month every two or three years became necessary.

  It was later noted that a correct compensation could be obtained by inserting one month for three times, in a cycle of eight years. By this, at the end of the cycle the difference was of 87 days.

  This 8-year cycle called octaeteris, includes the 99 lunations after which, ​​the same lunar phase is performed in the same month of the year that began the previous cycle, with a difference of one day and a half. On the basis of the estimated half of this cycle, the Greeks fixed the date of their quadrennial games.

  In 433 BC, the Athenian astronomer Meton developed a more accurate compensation system based on a 19 year cycle, in which one month was inserted seven times.  His system exceeded octaeteris cycle, reducing the difference to two hours and five minutes.

  The fact that the cycle of the Sun and Moon coincided almost exactly every 19 years was already known by the Babylonians since the time of Nabonassar, very long time before Meton.

  The Hebrew calendar is based on the Metonic cycle, which they call גוחאדז"ט, Gou'hadzat. It is divided in common years or peshutim, and embolismic years or meubbarim, to which a thirteenth month is added.

  These years are the 3rd, 6th, 8th, 11th, 14th, 17th and 19th of the cycle, which has 12 years of 12 months, totaling 144 months, and seven years of 13 months, totaling 91 months. This makes 235 lunar months that coincide almost precisely with 19 solar years, being the difference of only 6 minutes and 35 seconds per year.

  The following tables show the equivalence between the years of the Bible calendar, and of the Hebrew and Assyrian-Babylonian calendars.

The first day of the year

  There are three celebrations of the first day of the year on the Hebrew calendar, each one of them with a different meaning. The beginning of the year as considered in Western culture, is identified with the celebration of Rosh Hashana (ראש השנה), on the 1st of Tishri; this is the first day of the year for legal contracts. The Mishnah (משנה: study, repetition) establishes it as the basis to compute the progression of the years and therefore, to calculate the Sabbatical year and the Jubilee. The book of Leviticus says: “The first day of the seventh month shall be for you a rest day commemorated with the sound of the horn; it will be a holy convocation”. (Leviticus 23:24) This first day of the year introduces the ten penitential days leading up to Yom Kippur, in which the Jewish people become aware of their behavior on the previous year and invoke the Lord's forgiveness.

  Another first day of the year is the 15th of Shebhat, the day of Tu B'Shvat (ט״ו בשבט), this is the first day of the year for trees, and is mainly linked to the agricultural year.

  In ancient Israel, this was the time to consign one tenth of the product of the year, which was divided according to the seven-year cycle of the Hebrew calendar. Each year the first tenth of the total product was entirely delivered to the tribe of Levi, and then, one-tenth of what was left, was assigned according to the year of the cycle. In the years 3rd and 6th it was distributed to the poor, and in the years 1st, 2nd, 4th, 5th, it was held by the producer, who had to consume it personally in Jerusalem. The 7th year was a sabbatical year and the earth products were not collected.

  The third first day of the year is on the 1st of the month of Nissan; the month that begins the religious year, as we read on the book of Exodus, which says: “This month shall be for you the head of the months, the first month of the year”. (Exodus 12:2)


The week

  Another feature of the Hebrew calendar is that the day starts when the sun sets, when the sky becomes dark enough to display three stars or planets.

  This practice is due to the commands of the Law given to Moses; the instructions for the Passover say: “The children of Israel must celebrate the Pesach in its due time. You shall celebrate it between the two evenings of the fourteenth day of this month, and you will fulfill all its mandates and requirements”. (Numbers 9: 2..3) Besides, Moses was told with regard to the Day of Atonement: “On that day you will do no work ... it will be for you as a Sabbath of rest... and you will rest from the sunset of the ninth day of the month until the following sunset“. (Leviticus 23:28 and 32)

  All these instructions reflect that the day began in the evening after sunset, and ended at the next sunset.

  This table shows the week days of the Hebrew calendar and their correspondences.


  The first day of Nissan marks the beginning of all year festivities, which according to their meaning can be annotated as follows:


1)  The 14th of Nissan (initially called Abib), is the feast of the Passover (פסח). This is the first and most important celebration of the calendar, one of the three pilgrimage festivals, called Shalosh regalim (3 pilgrimages), in which all the people of Israel journeyed to Jerusalem to attend the Temple. This celebration reminds the liberation of Israel’s slavery in Egypt, provided by God through Moses.

  The seven days following the Passover are called Feast of Unleavened Breads. The first and last days are days of rest and require to abstain from work. In the Book of Numbers 28:16..18 and 25 we read: “The fourteenth day of the first month will be held the Passover of Yahuh, and the fifteenth day of the month, the Feast of Unleavened Breads that must be eaten for seven days. The first day shall be a holy convocation and you will do no work of service... and the seventh day shall be a holy convocation for you, so you will not bear out any task of service”.


2)  In the month of Siwan, fifty days after Passover, starting from the following Saturday after the seven days of the unleavened bread, comes the feast of Pentecost, a term that comes from the Greek πεντηκοστῆς or pentekosté, and means “fiftieth” day. This feast called in Hebrew שָׁבֻעֹת or shavuot (weeks), refers to the seven weeks after the unleavened breads. In the Bible, the feast is connected to the first fruits of harvest. The Scriptures defines it as “the Feast of the Harvest, of the first fruits of what you have sown and cultivated in the field”. (Exodus 23:16)


3) The 17th day of Tammúz (שבעה עשר בתמוז, Shiv'ah Asar b'Tammúz) is a fast day in memory of the fall of Jerusalem.


4)  The 9th day of ‘Abh is a fast day in memory of the destruction of the Temple.


5)  The 1st day of Tishrí is the celebration of Rosh haShana, the second first day of the year (ראש השנה). The Israelites used to celebrate the first day of every month, called “new moon”, but as we read in Leviticus 23:23..25, the most solemn new moon was the “new moon of the seventh month”, greeted with the sound of the horn and celebrated as the first day of the civil calendar.


6)  The 10th day of Tishrí, is the Day of Atonement: (יֹום הַכִּפֻּרִים, yóm hakipurim). It is a day of fasting for purification, a day to humble oneself and be reconciled with God. In Leviticus 16:10 and 23:27..32, we read that the high priest symbolically loaded the sins of Israel upon a male goat that was forsaken in the moor.


7)  In the days 14 to 16 of Tishri, is the Feast of Tabernacles (סוכות, Sukkoth) or Feast of Harvesting. It is the end of the season for agricultural crops: grain, olives, fruit and vintage. The feast recalls the life of the people of Israel in the wilderness, who lived in huts or tents (Sukkoth) while traveling to the Promised Land.

  The tribes of Israel gathered to commemorate it and to renew their covenant with God.


8)   From the 25th of Kisléw to the 2nd of Tebheth, the Feast of Dedication (חנכהחג, Hanukkáh-hag) is celebrated as a reminder of the purification and re-consecration of the Temple of Jerusalem, on the time of the Maccabees. During these seven days the Hanukkah candelabrum is lit up.

  The historian Josephus Flavius ​​writes that in the 1st century AD, this celebration was also known as the “Feast of Lights”, because when the moment to relight the Temple's candelabrum came, the provision of pure ceremonial oil that was only enough for one day, miraculously lasted for eight days. In memory of this wonder, a nine arm candlestick is lit instead of the usual menoráh (מנורה) with seven candles, described in Exodus 25:31..40. The eight arms of the Hanukkiyah represent the light of the eight days, while the central branch called sammash or server, is used to light the flame on the arms.

  On the evening of Kisléw 25th the sammash is lit, then are lit the other eight candles, one each day. This feast was celebrated in the time of Jesus (John 10:22), and is still celebrated around the world by the Israelites.


9)   The 10th of Tebheth is Fast Day, in remembrance of the Babylonian siege of Jerusalem.


10) The Feast of Purim (פורים: lots) is celebrated on the14th and 15th of Adhar. Its origin is reported on the Book of Esther. The fast on the 14th lengthens from dawn to sunset and is called “Fast of Esther”, in memory of the fast of Esther and Mordecai, when Haman, the counselor of King Ahasuerus (אֲחַשְׁוֵרֹושׁ ʾăḥašwērôš, or Xerxes 1st), plotted the destruction of the Hebrew people, by convincing the king of the need to eliminate them.


11)  All Saturday (שַׁבָּת, Sabbath: cease or rest) must be observed. The Sabbath was a day of required rest in remembrance of the Creator's rest after his creation periods. It was a day of joy, a day to rest from daily work. The requirement of observing the Sabbath is the second mandate of the Law that God gave to Moses, and it says: “Remember to sanctify the Sabbath day, you will work for six days and deal with all your tasks, but the seventh day is a Sabbath for your God Yahuh”. (Exodus 20:8..10)

  The Sabbath begins at sunset, with the ceremony of “lightning the lights”, and ends after the next sunset, with the recitation of Havadalah, which is the formula for the closing of all celebrations.



  Zenith is the intersection of the vertical between a place and the visible celestial hemisphere. It is the highest point in the sky, 90° right over the head of the observer; the vertical of a place that cuts the celestial sphere in two points.

  The name derives from the Arabic term samt al-ra's (head direction), where the word samt is a transliteration of the Greek term semeion. The Latin transliteration was from the Italian mathematician and astronomer Tiburtinus Plate (1116-1138), who used the word “zenith capitisor “zenith capitum”.


  The point diametrically opposite to the Zenith is the Nadir. Zenith and Nadir are the poles of the horizon. Nadir is the point at the antipodes of the zenith; it represents the absolute South and the intersection of the perpendicular to the horizon, passing through the observer, with the invisible sky hemisphere. The word derives from the Arabic al-samt nazir, meaning “corresponding to the zenith”, or to the direction of the head.

The word Tropic comes from the Latin tropicus, which comes from the Greek τροπικός: tropikόs, meaning rotation.

 The Tropics are the parallels of latitude 23°26'16" north and south, corresponding to the inclination angle of Earth's axis with respect to the perpendicular orbital plane. These represent the maximum latitude North and South of the equator, where only its zenith can arrive. This occurs in both hemispheres at the time of their respective summer solstice, around June 21st in the northern hemisphere, and December 21st in the southern hemisphere.