The Western calendars are based on the Gregorian solar calendar of 365 days (Wikipedia Gregorian calendar).
Othes countries use the lunar calendar. The lunar year has between 354 and 355 days. There is therefore a difference of about 11 days between the solar calendar (365 days) and the lunar calendar (354 days). Nevertheless, the Hebrew lunar calendar, also takes into account the solar cycle of 365 days, so it is a "lunisolar" calendar (Wikipedia Hebrew lunar calendar).
The important points to know about the biblical calendar, like the Hebrew calendar, are the following (important to understand the biblical reasoning that will follow):
In the Bible, the days begin in the evening after the sunset. For example in Genesis 1:5, regarding the first day of the symbolic “And there was evening and there was morning, a first day".
In the Bible, the months began at the "new moon" (Psalms 81:3). Lunar months are either 30 or 29 days.

Nevertheless, at this stage of the study, there is a significant difficulty regarding the biblical definition of the new moon (Wikipedia New Moon). Some think that this is the moment when the moon completely disappears (in the current Hebrew calendar). Others think that this is the first crescent of the moon. For this reason, there is a special study of the theme of the New Moon that will indicate the necessary and important choice between these two options to determine exactly a biblical date (that of the memorial to the death of Jesus Christ (Nisan 14th) and Tishri 10th) (After this article (below)).


The lunar year has 12 months of 29 or 30 days. The intercalary month (Veadar) is regularly added to compensate for the difference of 11 days between the lunar year (354 days) and the solar year (365 days). In this case, this year has exceptionally 13 months, it is a “lunisolar”. In the Bible there is no direct mention of this process in order to adjust the lunisolar calendar to the solar year. Nevertheless, indirect information shows that this adjustment was made. For example, some months had to coincide regularly with seasonal crops, either spring (Abib (Nisan): spring) or autumn (Ethanim (Tishri): autumn) (Exodus 23:15). It is obvious that the Israelites of the biblical times realized this adjustment by the addition of the intercalary month (Veadar). The festivals celebrated the month in spring, remained spring, over the years. And all the autumn festivals of the month of Tishri, remained autumnal, over the years (Leviticus 23:37).

Currently the adjustment system, used by the Hebrew calendar, is made with a “metonic cycle”: 7 adjustments with 7 lunisolar years of 13 months, over a period of 19 years.

In the book of Ezekiel we can understand that the year in which the Great Tribulation will occur will be Lunisolar, with 13 months, according to the Jewish calendar. In Ezekiel chapters 38 and 39 we have the prophetic story of events before, during and after the Great Tribulation. After the Great Tribulation the prophecy gives the information of a seven-month period of cleansing the Earth: "The house of Israel will spend seven months burying them in order to cleanse the land" (Ezek. 39:12-14). How would this simple information make us understand that this would be a year of 13 months?

According to Revelation 11:19 the Great Tribulation will take place a Tishri 10th. At the end of the seven months written in Ezekiel 39: 12-14, it is written that the prophet had the vision of the Temple which represents the dominion of the Kingdom of God on earth, a certain in Nisan 10th: " In the 25th year of our exile, at the beginning of the year, on the tenth day of the month, in the 14th year after the city had fallen, on that very day the hand of Jehovah was upon me, and he took me to the city" (Ezekiel 40:1)

The simple cross-checking of information from the 7 months period, with the period from Tishri 10th to Nisan 10th (6 months normally), we understand that there will be the intercalary month of Veadar: The year when the Great Tribulation will take place will be a Lunisolar Year of 13 months.

Astronomical table of the lunar cycle of May 2019

Hebrew Calendar - Chiourim - May 2019 (written in french) (Nisan / Iyar 5779):
Two days late with the biblical system of the new moon (Psalms 81:3)

New Moon

"Blow the horn on the new moon, On the full moon, for the day of our festival"

(Psalms 81:3)

There are two definitions of the new moon:

1 - "The new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the unaided eye, except when silhouetted during a solar eclipse. Daylight outshines the earthlight that dimly illuminates the dark side of the new Moon. The actual phase is usually a very thin crescent because the Moon rarely passes directly in front of the Sun, except in a solar eclipse" (Wikipedia New Moon).

2 - "The original meaning of the term new moon, which is still sometimes used in non-astronomical contexts, was the first visible crescent of the Moon, after conjunction with the Sun. This crescent Moon is briefly visible when low above the western horizon shortly after sunset and before moonset" (Wikipedia New Moon).

The first definition of the new moon, is corroborated by what is written in Psalms 81:3: "Blow the horn on the new moon, On the full moon, for the day of our festival". According to the context of this Psalm, it is the festival of booths which was celebrated from Ethanim 15th (Tishri 15) to Ethanim 22nd. It was an autumn festival, in the time of the last harvests. While the festival of unfermented cakes, was celebrated from Nisan 15 to 22, in the spring, at the beginning of the first harvests.

In Psalms 81:1 it is written: "Shout joyfully to God our strength. Shout in triumph to the God of Jacob". The festival that most symbolized the joy and exuberance, was undoubtedly the fest of booths. Regarding it, Jehovah had told Moses, for his people Israel: "Seven days you will celebrate the festival to Jehovah your God in the place that Jehovah chooses, for Jehovah your God will bless all your produce and all that you do, and you will become nothing but joyful" (Deuteronomy 16:15 (see verse 13)). The expression of Psalms 81, "Shout joyfully to God our strength", describes perfectly the feeling of joy asked by God, in Deuteronomy 16:15. The complete appearance of the "full moon", marking the middle of the lunar month, is in the poetic contrast to the "new moon", which is at this stage, invisible, and represents the start of the month.

Looking at the astronomical tables of the lunar cycles, if we go back, starting from the full moon (whether it's the Tishri, 15 or the Nisan, 15), we arrive at the beginning of the month, at the new moon, at the moment "when the Moon and Sun have the same ecliptic longitude" and therefore, it is invisible ( In the example presented in the photo (above), of the lunar cycle of May 2019: After the sunset of May, 17 to May 18, is the full moon, biblically speaking, the 15th of the month of "Iyyar" (or Ziv), of the Hebrew month. Going back fifteen days, we reach the date of Iyyar 1st (biblical month), May 3rd, 2019 (gregorian calendar), after sunset.

Nevertheless, in the current Hebrew calendar (Hebrew Calendar - Chiourim (In French)), Iyyar 1st is after the sunset of May 5th to May 6, 2019, there are two days late (See photo to the right). In this case, it is the chosen option of "the first visible crescent of the Moon" (see photo above, comparing it to the Hebrew Calendar (in Jerusalem). What option to choose? The invisible new moon or the first visible crescent?

The Biblical Tishri 10, corresponds to 22 (after sundown) / 23 September 2023, the date from the summer solstice to the autumnal equinox (early winter, according to the Bible (Zechariah 14: 8 ))

Hebrew Calendar - Chiourim - September 2023 (Elul / Tishri 5783),
10 Tishri corresponds to September 24/25, 2023 (two days late with the Biblical Tishri 10 (see photo above))

"It will happen in summer and in winter"

(Zechariah 14:8)


Jehovah clearly announces "His One Day" (14:7), the Great Tribulation, will take place in the day ot the change of season, from the summer solstice to the autumnal equinox (representing the beginning of winter, in the Bible), September 22nd (after the sunset) to 23rd (gregorian calendar). In many biblical quotes, it is known that the Great Tribulation will take place in Ethanim 10th (Tishri 10th), in a luni-solar year of 13 Biblical months. Regarding Zachariah 14:7,8 : The "one day" of Jehovah, the date of the great tribulation will take place : Tishri 10th = September 22/23.

Starting from these three extremely important Biblical information, it is sufficient to look first in the current Jewish calendar (Hebrew Calendar - Chiourim (written in french)), in what luni-solar year of 13 months, the Ethanim, (Tishri 10), corresponds to the September 22nd and 23rd, the date of the transition from the summer solstice to the autumnal equinox. Based on this official Jewish calendar, we must search until the year 2034, where Tishri 10th exactly corresponds from Friday, September 22 (after sunset) to Saturday, September 23, 2034.

Regarding the other biblical method based on the astronomical new moon, we get the date from Friday, September 22 (after sunset) to Saturday, September 23, 2023 (which is a luni-solar year), corresponding to the biblical Ethanim,10 (Tishri,10). How to obtain the Ethanim 1st (Tishri 1st)? We must take into account the annual alternation of lunar months given its duration of 29 days and a half (this half day must be integrated every other month): a lunar month of 30 days, followed by a month of 29 days, etc. The alternation of the beginning of the biblical year (which begins in Nisan), to the month of Tishri is the following: Nisan: 30 days , Iyyar (or Ziv): 29 days, Sivan: 30 days, Tammuz: 29 days, Ab: 30 days, Elul: 29 days and Ethanim (or Tishri) 30 days.

To get exactly Ethanim 1st (Tishri 1st) 2023, just start with the new moon of the previous month, Elul 1st, which, given the annual alternation, has only 29 days, which allows to obtain the Tishri 1st. The new moon corresponding to Elul 1st, will be in the day of August 16, 2023 (gregorian calendar). That means, Elul 1st will begin on August 15th, after sunset, to August 16, 2023. Adding, 29 days, in accordance with the annual alternation, the 29th of Elul will be the in September 12th (after sunset), to the 13th of September 2023.

So, Ethanim 1st (Tishri 1st), in September 13th (after sunset) to September 14th. Therefore, the Biblical Ethanim 10th (Tishri 10th), will be: Friday, September 22nd (after sunset), to Saturday, September 23rd, 2023.

Comparing this date with the Hebrew calendar Chiourim, there are two days late in this calendar: September 22/23, 2023 corresponds to Tishri 8th. It is the biblical option of the new moon (without visible crescent) that was chosen for the calculation of the date of 22/23 September 2023 (Psalms 81:3). It is on this same biblical basis of calculation that the date of the next commemoration of the death of Jesus Christ is determined on Sunday, April 5, 2020, after sunset.



A fourth biblical information allows taking into account the calculation of the date of September, 22/23, 2023, corresponding to the Biblical Ethanim 10 (Tishri 10): The prophecy of Daniel chapter 8:23-25, in connexion with the description of the last king, who will face the King Jesus Christ during the great tribulation:

"And in the final part of their kingdom, as the transgressors act to a completion, a fierce-looking king who understands ambiguous sayings will stand up. His power will become great, but not through his own power. He will bring ruin in an extraordinary way, and he will be successful and act effectively. He will bring mighty ones to ruin, also the people made up of the holy ones. And by his cunning he will use deception to succeed; and in his heart he will exalt himself; and during a time of security he will bring many to ruin. He will even stand up against the Prince of princes, but he will be broken without human hand" (Daniel 8:23-25).

Everything indicates that it is the "king" or the president of the United States: Mister Donald Trump. Be that as it may, he must be re-elected in a second term, because the year 2023 will be almost at the end of his future second presidency. His re-election will be a double biblical confirmation: First, that he is indeed the last king of the last world power, mentioned in the prophecy of Daniel 8: 23-25. Second, that the date of Friday, September 22 (after sunset), September 23, 2023, for the Biblical Ethanim 10 (Tishri 10), is the date of the future worldwide great tribulation (Matthew 24:21). Let us look forward to the outcome of the US elections of November 3, 2020 (Revelation 3:3): "For the Sovereign Lord Jehovah will not do a thing Unless he has revealed his confidential matter to his servants the prophets" (Amos 3:7).