Is the Law of Moses based on the lunar calendar?

According to Genesis 8:3-4 the ark of Noah rested on Mount Ararat "on the 17th day of the seventh month."

Genesis 8:3-4 (NASB)
3 and the water receded steadily from the earth, and at the end of one hundred and fifty days the water decreased. 4 In the seventh month, on the seventeenth day of the month, the ark rested upon the mountains of Ararat.

In other words, prior to the grounding of the ark on Mount Ararat the flood had started 150 days earlier "on the 17th day of the second month."

Genesis 7:11 (NASB)
11 In the six hundredth year of Noah’s life, in the second month, on the seventeenth day of the month, on the same day all the fountains of the great deep burst open, and the floodgates of the sky were opened.

So from the 17th of the second month (beginning of flood) to the 17th of the seventh month (ending of flood) the text indicates five months, which was 150 days. Therefore we infer that the month was based on the lunar calendar. However, in this context of these passages in Genesis, is the last day counted?

For example, if the last day in fact is counted, then Noah's Ark grounding on Mount Ararat would have been the 151st day. Is this the appropriate approach to counting months and weeks in the lunar calendar in the Mosaic Law?

  • There's a debate between the Karaite Jews and Rabbanite Jews on how to calculate the calendar. Karaites insist on physical observation of the moon (which rabbanites admit used to be how it was done) while rabbanites use a mathematical formula decided on by the president of the last functioning Sanhedrin (who lived 400-425). Commented Sep 5, 2014 at 4:44
  • 2
    @davidbrainerd. Yes, but in both cases it is a lunar, or more precisely, a luni-solar calendar. Recent research shows (by the way) that the present rabbinic calendar, based on arithmetic calculation of the molad, is not attestable before the 9th century CE.
    – fdb
    Commented Sep 7, 2014 at 12:26
  • Forty-nine lunations are exactly two weeks short of a Julian cycle. The error of this approximation amounts to about a day in three and a half millennia.
    – Lucian
    Commented Jul 30, 2017 at 17:21

3 Answers 3


You are correct to say that the two verses in Genesis imply that the time from the 17th day of the 2nd month to the 17th day of the 7th month is exactly 5 x 30 = 150 days; that is: each month is exactly 30 days. What you overlook is that in a lunar calendar the time from one sighting of the new moon to the next sighting will be 30 days in about half of the months and 29 days in about half of the months. (This is because the true synodic month is 29.53059 days, as has been known at least since the time of Hipparchus). Thus, 5 lunar months are actually about 147 or 148 days. The discrepancy in the Genesis text has been commented on for centuries; the Rabbinical tradition explains it with the assumption that because the sky was clouded Noah could not see the new moon and consequently assigned each month the maximum length of 30 days. Another possibility is that “150 days” simply means “about 150 days”; the text is thus not actually about calendar months but about a rough estimate of the elapsed time. The latter is broadly speaking the position taken by Bruce K. Gardner, The Genesis Calendar: The Synchronistic Tradition in Genesis 1-11 (Lanham, MD: University Press of America, 2001).

We have recently discussed a closely related question here: Ancient Hebrew Calendar(s) and Modern Translations of "Years". You might want to look at my answer to that question and the recent scholarly literature mentioned there.


The answer is Lunar Shabbat(Genesis 1:14) with complete and incomplete weeks (Leviticus 23:15). This means that Shabbats are always on 1-8-15-22-29th of the month. There are 4 complete weeks in a month, and sometimes there can be incomplete weeks (1-2days + New Moon Shabbat). This also means that Hebrew month can never be 30 days, otherwise we would have 2 Shabbats in a row (29th+New Moon).

Click here to see my reconstruction of the calendar. Calculate the days and it will be exactly 150 if you count end date (inclusive counting). Here is the result

  • Welcome to Stack Exchange, we are glad you are here. Be sure to check out the site tour and read how this site is a little different than other sites. Could you further explain Lunar Shabbat and Complete and Incomplete weeks? Occasionally answers will be removed if they are a "link only answer" and I fear that this could be the case with this answer without a little exposition. Commented Jan 28, 2016 at 16:36
  • 1
    @AleksandrSigalov Welcome to Biblical Hermeneutics Stack Exchange! I'm very grateful for your participation here. :) Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here (summarize the relevant portions of the resource that answer this question), and provide the link for reference. Commented Jan 28, 2016 at 17:41
  • @PaulVargas - I thought about asking that too, but looking at the Links, it would take some engineering to convert these HTML5 widgets into something that will fit within the markdown restrictions here. Commented Jan 28, 2016 at 20:41
  • The target of the "Click here" link no longer exists, making this answer somewhat useless. Commented Jul 27, 2019 at 13:34

Because God is revealing to you that his calendar is based off the lunar phases and not the solar phases. Psalms 104:19 "he (God) appointed the MOON for MOEDIM". God gave you specific dates so that you could prove his calendar has never changed. Most bible scholars falsely claim that during the pre-flood era, there were exactly 30 days per month and 360 days per year. This is not true and easily proven false by Noah's flood account. Let me show you, and prove Gods calendar is based of the lunar phases.

Gen. 7:11 - The rain started in the 2nd month, 17th day.
Gen. 7:12 - It rained 40 days and 40 nights.
Gen. 7:24 - Then, the waters "prevailed" 150 days.
Gen. 8:3 - Then, the waters "abated" 150 days.
Gen. 8:13 - Waters dried on the 1st day of the new year.

These facts reveal that between the 17th day of the 2nd month and the last day of that year, totaled 340 days. But then add the first 16 days of the 2nd month that weren't counted, and then add the 29 days in the first month (Hebrew months had 29 or 30 days per month), and you get a total of 385 days.

Now ask yourself, are there 385 days in a single year, in your pagan solar calendar? Nope. I just showed you how there were 385 days in a year during the life of Noah, this proves a 13th month was present during the times of Noah. This also proves that it is impossible for every month to be exactly 30 days long. The ancient Hebrew calendar had either 354 days per year (totaling 12 months) or 384-385 days per year (totaling 13 months).

The chronological facts that are recorded in the account in the book of Genesis clearly establish a period of 385 days in the year of the Noachian Flood. This year length is significant because it is the exact number of days required for an excessive leap year in the Hebrew Calendar. This remarkable account of the Flood, which God inspired to be recorded in His Word, is indisputable evidence that the Hebrew Calendar bears His stamp of approval. There can be no doubt that the calculations of the Hebrew Calendar have been the basis of God’s true calendar from the beginning.

Now back to my statement about our calendar being dictated by the MOON. God commanded in Psalms 104:19 "I appointed the MOON for MOEDIM". So what are Gods MOEDIM that must be appointed according to the MOON (not the SUN)? Leviticus chapter 23 lists a total of 8 MOEDIM that are to be appointed according to the MOON. The 7th day Sabbath is the very first MOEDIM listed in Lev.23 to be appointed by the moon, not the solar cycle like pagan Rome enforced in the 4th century under emperor Constantine, and accepted by the Roman Catholic Church. Now think back to Daniel 7:25, when God warned us how we know if we have been deceived by the Devil. Daniel 7:25 "The BEAST will think to CHANGE my TIMES and LAWS". I just showed you how the Roman Catholic church, paired with Constantine, changed Gods "TIMES". They switched Gods luni-solar calendar to a "solar only" calendar. This was only possible when Emperor Constantine declared under penalty of death, that no one could obey the "Jewish" holy days. This eliminated the "New Moon Day". Which starts the beginning of all of Gods months. Ezekiel 46:1 tells us there are 3 types of days (New moon day, 6 work days and then a 7th day Sabbath). Rome enforced the elimination of the new moon day, meaning the 6 work days started a day earlier than God scheduled, making it so the 7th day Sabbath was now to be calculated according to a 7 day weekly cycle, according to the sun, not moon. Be aware and do not learn the ways of the heathen. Even Zechariah 14:16 promises us that when Jesus returns, all nations must obey the feast days (according to the moon/Psalms 104:19) and Zechariah 14:21 says that when Jesus returns to earth we all must obey the new moon days and Sabbaths AND we will still bring sacrifices to him.

The word "Christian" was only used 3 times in the bible. We are told a Christian is someone who "obeys and teaches everything that Jesus did and taught". Jesus taught the feast days, the MOEDIM, according to the MOON, just like his father commanded in Psalms 104:19. It wasn't until about 300 years AFTER the death and resurrection of Jesus that any country in this world switched to a SOLAR BASED CALENDAR! Don't be fooled.

During the Exodus from Egypt, we are told the 15th day of the 1st, 2nd AND 3rd month were Sabbaths. This is impossible on a solar, 7 day weekly cycle calendar. Wake up friends, God does not calculate his Sabbaths according to the sun cycle like pagan sungod worshipers do. God commanded his 7th day Sabbath to be appointed according to the moon, just like the Passover, unleavened bread, first fruits, weeks, trumpets, atonement, and tabernacles. "I appointed the MOON for MOEDIM". The Sabbath is literally defined as Gods very first MOEDIM, which means it MUST be appointed by the MOON.

  • God's inspired scriptures accurately record many things without the implication that what it describes is inspired. It does seem plausible that the calendar of Noah's time used leap months. That doesn't make such a calendar any more God inspired than a solar calendar. Of course if the calendar was purely lunar there would be no reason for leap months. And Genesis 1:14 says all the lights are for the moedim.
    – curiousdannii
    Commented Jul 27, 2019 at 8:34
  • v. 12 indicates that the rain was upon the forty days. This indicates the end not the beginning of a 40 day period.
    – David
    Commented Feb 19 at 10:10

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