(Crossposted to Mah Rabu.)
So the world didn’t end yesterday. To be fair, they weren’t actually predicting the end of the world until October 21, at the conclusion of five months of torment for those of us left behind. Yesterday was supposed to be only Judgment Day. But that didn’t happen either.
Of course this is all nonsense, but we can check their math and see whether it is at least internally consistent nonsense.
Let’s start with the year:
According to the tract explaining the calculations, the world was created in 11,013 “BC”, so we are now in the year 13,023 from creation. (It’s one less than you think because there was no year zero; 1 BCE was followed immediately by 1 CE.) The biblical flood occurred in the year 4990 “BC”, 6023 years after creation. God says in Genesis 7:4 that the flood will come in 7 days, and since one day to God is like 1000 years to us (they cite a New Testament verse for this, but we have the same idea in Psalm 90:4), this means the world will be destroyed 7000 years later, which comes out to 2011 CE.
I was baffled at how they arrived at this year count in the first place. According to the Jewish calendar, we are now in the year 5771 from creation, and the flood took place in the year 1656 from creation (4115 years ago, or 2105 BCE). While the exact count of the number of years from “creation” is somewhat controversial (particularly at the interface between biblical chronology and real history), counting the years in Genesis from creation to the flood is very easy, since we have a detailed list of how long each ancestor lived before the next generation was born. Assuming they’re reading the same Bible (and I just checked the King James and the numbers are the same), it’s hard to see how the totals could be off by so much. At first glance I thought they were just applying the same principle that 1 day to God is 1000 years to us, so the six days of creation would add an extra 5999 years (subtract one because, according to the rabbis, humans were created on Rosh Hashanah of the year 2, so creation began on 25 Elul of the year 1). But that can’t be it, because the time from the end of creation to the flood has to be much more than 24 years.
So I did some googling and it turns out that they get this chronology based on a general principle that a generation is a lifespan, so in these biblical genealogies, we can assume that the son was born in the year that the father died. For example, since Genesis 5:11 says that Enosh lived 905 years, they ascertain that the time from Enosh’s birth to his son Kenan’s birth was 905 years. Thus they completely disregard the explicit statements in Genesis 5:9-10 that Enosh lived for 90 years and then fathered Kenan, and then lived 815 years after that. By this method, they arrive at a stretched-out chronology. If they hadn’t done this, then the 7000-year anniversary of the flood wouldn’t take place until 4896 CE, so the end would be far from nigh.

Now let’s look at the day of the year.
According to Genesis 7:11, the flood began on the 17th day of the 2nd month. In the Hebrew calendar, even though the year begins in Tishrei (in the fall), the 1st month is Nisan (in the spring), and so we observe all the biblical holidays accordingly: Pesach (in “the first month”) in Nisan, and all the holidays of the “seventh month” in Tishrei. Based on this, the 2nd month would be Iyar, and yesterday (May 21, 2011) was indeed the 17th of Iyar, which would make it the anniversary of the flood by this count.
But it’s not that simple. First of all, yes, yesterday was 17 Iyar for the Jews, and that’s based on Rosh Chodesh Iyar having been on Thursday, May 5. But the actual astronomical new moon was on Tuesday, May 3. In our calendar algorithm, Rosh Chodesh is frequently observed later than the actual new moon due to various considerations: for example, Rosh Hashanah in the coming year will be on Thursday rather than Wednesday, so that Yom Kippur will not fall on Friday, immediately before Shabbat. By stating that yesterday was the 17th of the month, are these Christians endorsing rabbinic rules that were instituted centuries after the Jewish-Christian split?
Second of all, it’s not so clear that “the second month” in this context would be Iyar. In Exodus 12:2, God commands very clearly that “this month” (the month in which Pesach takes place, in the spring, understood to be Nisan) shall be the first of months. But the rabbis are split on which month was the first month before this command was given. In a baraita at Rosh Hashanah 10b-11a, Rabbi Eliezer says the world was created in Tishrei, and Rabbi Yehoshua says the world was created in Nisan. In another baraita at Rosh Hashanah 11b, it is made clear that in dating the flood, both of them count the months from creation. Since the flood began on the 17th day of the 2nd month, Rabbi Eliezer places it on 17 Cheshvan (the 2nd month starting from Tishrei), and Rabbi Yehoshua places it on 17 Iyar (the 2nd month starting from Nisan).
The May 21 doomsayers seem to be following R. Yehoshua, so they have some support for their position, but it is R. Eliezer’s view that has survived in Jewish tradition. Rosh Hashanah (1 Tishrei), not Nisan, is when we mark the anniversary of the world’s birth. The date 17 Cheshvan also comes up in Mishnah Ta’anit 1:4. The rainy season in Israel begins in Cheshvan, and the Mishnah says that if it hasn’t rained by 17 Cheshvan, individuals begin fasting for rain. The Yerushalmi (Ta’anit 64a) connects this date directly to the beginning of the flood. This is not a stretch, since both the biblical flood story and the theology of Masechet Ta’anit see rain as something sent by God in response to human actions. You can’t make the same connection for 17 Iyar, which is nowhere near the rainy season.
If the anniversary of the flood is on 17 Cheshvan in 2011 CE, then it won’t occur until Monday, November 14. Still, it’s not surprising that the Judgment Day folks went with May 21 instead. In yet another baraita at Rosh Hashanah 12a, it says that the sages of Israel date the flood according to R. Eliezer, and the sages of the nations of the world date the flood according to R. Yehoshua.
Finally, what’s up with October 21, 2011, as the end of the world?
They cite a verse from Revelation saying that people (excluding those who are raptured) will be tormented for 5 months after Judgment Day. Add 5 months to May 21 and you get October 21. Of course, this would be 5 Gregorian months, even though they got to May 21 in the first place by using the Hebrew calendar (and 5 lunar months after 17 Iyar would be 17 Tishrei, or October 15, 2011). But the Gregorian calendar is the Christian calendar, so we’ll give them that one.
But then they note that “October 21st of 2011 is also the last day of the Biblical Feast of Tabernacles”, and see eschatological significance in this (which, to be fair, we do too — check out Zechariah 14, the haftarah for the first day of Sukkot). Except that they’re wrong. Depending on how you look at it, “the last day of the Biblical Feast of Tabernacles” could refer to the 7th day of Sukkot (21 Tishrei) or to Shemini Atzeret (22 Tishrei). But October 21, 2011, is 23 Tishrei, the day that some Diaspora Jews observe as the 2nd day of Shemini Atzeret, or “Simchat Torah”. Even though this is still a holiday for some, no one would consider it to be a day of Sukkot: e.g., even though some have the practice of still eating in the sukkah on 22 Tishrei, no one does on 23 Tishrei. And even if some did, they’re talking about the biblical festival. There’s no way that Christian eschatology incorporates yom tov sheini, and in any case, the apocalypse should be centered on the land of Israel, where all agree that 23 Tishrei is not a holiday. So instead, they should expect the end of the world anywhere between October 15 (the 3rd day of Sukkot, 5 lunar months after 17 Iyar) and October 20 (Shemini Atzeret, the latest day that could reasonably be considered “the last day of the Feast of Tabernacles”).