The Creation of the “Permanent” Calendar

calendar-1568148-639x424When the Torah commands us to create a calendar, it includes two different responsibilities: First, to have Rosh Chodesh and the length of each month determined on the basis of when the new moon appears, and, second, to have the holiday of Pesach fall in the spring and the holiday of Sukkos in the autumn (in the northern hemisphere). Thus, we have two separate and very different requirements, one of having the months determined by the moon, which is a little more than every 29½ days, and having years that coordinate with the seasons, which follow the solar year, which is a bit less than 365¼ days.

To accomplish that the dates and holidays should fall according to the seasons, the halacha is that some years have 12 months, or approximately 354 days, and others have 13 months, or approximately 384 days. This ensures that the holidays fall in their appropriate seasons. The mitzvah of the Torah is that the head of the Sanhedrin should be in charge, every month, to decide whether a month is 29 days long or 30, and of deciding whether a year should have an extra month. In the latter case, he appointed a special committee, comprised of members of the Sanhedrin, to review the relevant information and determine whether the year should be 13 months (a leap year) or only 12 (a common year).

By the way, after the destruction of the Beis HaMikdash, the main Beis Din was not located in Yerushalayim, but wherever the Nasi of the Jewish people resided, as long as it was in Eretz Yisrael. This included several communities at various times of Jewish history, including Teverya, Yavneh, and Shafraam.[i] Indeed, during this period, if the head of the Beis Din was in the Diaspora and there was no one of his stature remaining in Eretz Yisrael, the special Beis Din met outside the land of Israel.[ii]

Initially, all these decisions were made by the heads of the Sanhedrin, and, indeed, when Moshiach comes, we will again have this system. This was the system in place for thousands of years – from the time of Moshe Rabbeinu until about 250 years after the destruction of the second Beis Hamikdash. At that time, the head of the Sanhedrin, Hillel Hanasi (not to be confused with his ancestor, Hillel Hazakein), realized that, because of Roman persecution, the Sanhedrin’s days were numbered and it would be necessary to switch to a different system for determining the calendar. Hillel Hanasi implemented a temporary Jewish calendar, which is the one that we currently use. Although many people refer to it as a “permanent calendar,” it will be in use only until we again have a Sanhedrin, which will then be in charge of the calendar.

Hillel’s calendar kept the same basic structure of 29- and 30-day months and 12- and 13-month years, but it is based purely on calculation and not on observation. The two major changes in this new calendar are:

  • A Leap of Fate

The leap years now occur following a regular pattern of seven leap years and 12 non-leap (usually called “common”) years in a 19 year cycle. The third, sixth, eighth, eleventh, fourteenth, seventeenth and nineteenth years of the cycle are always leap years, and the rest are common years. This year is the nineteenth year of the cycle, and thus is a leap year.

  • The Haves versus the Have-nots

The length of most months is now predetermined. Tishrei, Shvat, Adar Rishon (which exists only in a leap year), Nissan, Sivan and Av always have 30 days; whereas Teiveis, regular Adar (in a common, non-leap year), Adar Sheini (in a leap year), Iyar, Tamuz and Elul are always only 29 days long. The two months of Cheshvan[iii] and Kislev are the only months whose length varies, sometimes 29 days and sometimes 30.[iv] A year in which both Cheshvan and Kislev have only 29 days is called chaseirah, lacking or defective; one in which Cheshvan has 29 days and Kislev has 30 is called kesidrah, as expected or regular; and one in which both Cheshvan and Kislev have 30 days is called sheleimah, full or excessive.

The terms chaseirah, kesidrah, and sheleimah apply in both common and leap years.[v] Thus, in the new calendar, all common years are either 353 days (if both Cheshvan and Kislev have 29 days), 354 days (if Cheshvan has 29 days and Kislev has 30) or 355 days (if both Cheshvan and Kislev have 30 days); all leap years are either 383 days (if both Cheshvan and Kislev have 29 days), 384 days (if Cheshvan has 29 days and Kislev has 30) or 385 days (if both Cheshvan and Kislev have 30 days). Since Adar in a common year always has 29 days, Adar Rishon always has 30 days, and Adar Sheini always has 29 days, like the regular Adar, the addition of an extra month of Adar in a leap year always adds exactly thirty days.

(Because the nineteen-year cycle synchronizes the lunar calendar with the solar year, the Hebrew and English dates of births, anniversaries and other occasions usually coincide on the nineteenth anniversary of the event. If yours does not, but is off by a day or two, do not fret. Your record keeping is accurate, but the cycle of nineteen years only relates to whether it is a leap year, not to whether the years are of the exact same length. The lengths of Cheshvan and Kislev are determined by other factors, and this will affect whether your 19th, 38th or 57th birthday or anniversary exactly coincides with its Hebrew/secular counterpart, or whether it is slightly off.)

The new calendar bases itself on an estimate, an average time that it takes the moon to revolve around the Earth. This molad calculation is that each new moon appears 29 days, 12 hours, and 793 chalakim (singular: chelek) or 793/1080 of an hour after the previous new moon. Once one knows when the new moon, called the molad, occurred on the previous Rosh Hashanah, one could now add either 12 or 13 times the above figure and determine the time of the molad in the next year, which is the most important factor in determining the date of the next Rosh Hashanah. (The term chelek, used on Shabbos Mevorchim when announcing when the molad is, equals 1/1080 of an hour, or 3 and 1/3 seconds.)

There is one other factor: Sometimes Rosh Hashanah takes place not on the day of the molad, but the next day, because the molad occurred on the afternoon of Rosh Hashanah and would not be visible in Eretz Yisrael until the next day. When Rosh Hashanah was determined by the observation of witnesses, this information was important not only in determining when Rosh Hashanah falls, but also for interrogating potential witnesses testifying to the appearance of the new moon. However, Hillel’s calendar is no longer dependent on witnesses, Rosh Hashanah is still not established on a day when the molad falls on its afternoon, but is postponed. Based on this information, one can determine which day should be Rosh Hashanah in the coming year.

Another major innovation

Did you ever notice that Yom Kippur never falls on Friday or Sunday? If it did, we would observe two consecutive days that both have the stringency of Shabbos. Indeed, when the calendar was based on observation, this could and did happen.[vi]

However, Hillel Hanasi’s calendar included some innovations that were not part of the earlier calendar. His calendar does not allow Yom Kippur to fall on either a Sunday or a Friday, thus avoiding the difficulty of having two Shabbos-like days fall consecutively. Hillel Hanasi’s calendar also does not allow Hoshana Rabbah to fall on Shabbos, which would cause the cancellation of the Hoshanos ceremony. As long as the calendar was determined on the basis of eyewitness testimony, it was halachically more important to have Rosh Chodesh fall on its correct day than to be concerned about difficulties created when certain holidays fall on or next to Shabbos.[vii] However, once we are fulfilling the mitzvah in a less-preferred way with Hillel’s “permanent” calendar, keeping Yom Kippur from falling on Friday or Sunday, and Hoshana Rabbah from falling on Shabbos, are factors to be included in establishing the calendar.

In order to accommodate these innovations, Rosh Hashanah could fall only on Monday, Tuesday, Thursday or Shabbos, since if it falls on Sunday, Hoshana Rabbah falls on Shabbos; if Rosh Hashanah falls on Wednesday, Yom Kippur falls on Friday; and if Rosh Hashanah falls on Friday, then Yom Kippur falls on Sunday. This would mean that when Rosh Hashanah in the coming year would naturally fall on Sunday, Wednesday or Friday, an extra day is added to the calendar to make sure that Rosh Hashanah falls on Monday, Thursday or Shabbos instead.[viii] This calendar concept of guaranteeing that Rosh Hashanah not fall on Sunday, Wednesday or Friday is called לא אד”ו ראש, lo adu rosh, meaning that the beginning of the year, Rosh Hashanah, does not fall on א, the first day of the week, Sunday; ד, Wednesday; or ו , Friday. It is predominantly for this reason that there was a need to have Cheshvan and Kislev sometimes 29 days and sometimes 30, in order to make the exact length of the years flexible.

Although the innovation of adding one day to the year so that Rosh Hashanah not fall on a Sunday, Wednesday or Friday seems relatively simple, it sometimes leads to more complex considerations. In some years, adjusting Rosh Hashanah to avoid Sunday, Wednesday and Friday creates a problem in the year before or the year after. Since Hillel Hanasi’s calendar did not allow a common year to be longer than 355 days and a leap year to be shorter than 383 days, the only way to avoid problems is to plan the calendar an additional year in advance and adjusting the calendar appropriately. In order to accomodate all these various calendar requirements, Hillel Hanasi established four rules, called dechiyos, which, together with the sod ha’ibur calculation and the 19 year leap year rotation, form the basis for determining our calendar.[ix]

To explain how this works, let us choose a sample year in which the molad calculation for Rosh Hashanah fell on Wednesday evening, and Rosh Hashanah therefore falls on Thursday, which is what we would expect. However, the next year’s molad for Rosh Hashanah falls on Tuesday less than two hours before the end of the day. Although the molad falls on Tuesday, it is too late in the day for this molad to be visible in Eretz Yisrael, and therefore, Rosh Hashanah cannot occur before Wednesday. However, since Rosh Hashanah cannot fall on a Wednesday because of the rule of lo adu rosh, it must be pushed off to Thursday, or two days after the molad. For this reason, that year must have an extra day. However, each year is limited how long it may be. In order to accommodate the proper dating of the second year, the year prior would have to have more days than the calendar allows. In order to resolve this, the year before is made longer than necessary. What is happening is that one Rosh Hashanah is postponed to allow that the next Rosh Hashanah should fall out in an acceptable way.

As I mentioned above, although the leap years follow an absolute nineteen-year cycle, whether the year is chaseirah, kesidrah, or sheleimah is determined by the other factors we have noted, and therefore does not follow the nineteen-year pattern. Rather, one first calculates when Rosh Hashanah should fall out based on the sod ha’ibur, checks the rules of the dechiyos to see what adjustments need to be made, and then determines on which day Rosh Hashanah should fall. As a result, whether the year in question needs to be chaseirah, kesidrah, or sheleimah requires calculating not only this year’s schedule, but also the coming year’s calendar requirements.

Based on all these calculations, there are seven prototype years for a common year and seven for a leap year that fulfill the calendar rules. Each of these fourteen prototype “years” is called by a three letter acronym in which the first letter identifies the day of the week of the first day of Rosh Hashanah, the second letter denotes whether the year is chaseirah, kesidrah, or sheleimah, and the third letter identifies the day of the week of the first day of Pesach. No letter is used to denote whether the year is common or leap, because this is understood by knowing how many days of the week Pesach follows Rosh Hashanah. In a common year that is kesidrah, Pesach falls two days later in the week than Rosh Hashanah, and in a leap year, it falls four days later, the two additional days being the extra two days that the extra month of Adar Rishon, thirty days long, adds to the day of the week count. Of course, these calculations must be adjusted one day in either direction, if the year is chaseirah or sheleimah. Either way, calculating how many days are between Rosh Hashanah and Pesach tells us whether it is a common or leap year, so there is no need to include this in the acronym.

Thus, this year 5776 is known as בשז because Rosh Hashanah fell on Monday (ב), it is a sheleimah (ש) year in which both Cheshvan and Kislev contain 30 days, and the first day of Pesach falls on Shabbos (ז).

At this point, we have the basic information to figure out how our calendar operates. Although we may not realize it, we actually already have enough information at our fingertips that we could already calculate the calendars for the coming years – indefinitely.


We understand well why our calendar involves use of the solar year – after all, our seasons, and the appropriate times for our holidays, are based on the sun. But why did the Torah insist that our months follow the moon? It seems that we could live fine without months that are dependent on the moon’s rotation around the earth!

One answer to this question is that the waxing and waning of the moon is symbolic of our own our relationship with Hashem – which is sometimes better and sometimes less so. However, we know that we can always improve that relationship, just as the moon after its waning and almost disappearing always renews itself.


[i] Rosh Hashanah 31b

[ii] Berachos 63a; Rambam, Hilchos Kiddush HaChodesh 1:8

[iii] Although the correct name of the month is Marcheshvan, we will follow the colloquial use of calling it Cheshvan.

[iv] Rambam, Hilchos Kiddush Hachodesh 8:5

[v] By the way, because Kislev is sometimes 29 days and sometimes 30, the last day of Chanukah is sometimes on the second day of Teiveis, and sometimes on the third.

[vi] She’iltos of Rav Acha’ei Geon, #67; Rambam, Hilchos Shabbos 5:21; Ha’emek She’eilah ad loc., Note 22.

[vii] Ha’emek She’ailah ibid; Gri”z, Hilchos Kiddush Hachodesh

[viii] Rambam, Hilchos Kiddush Hachodesh 7:1.

[ix] Because these dechiyos are extremely technical, I did not explain all of them.

Why Parshas Naso Sometimes Introduces Shavuos

Question #1: In most years, the parsha of Bamidbar falls on the Shabbos before Shavuos, and Parshas Naso falls the Shabbos after Shavuos. However, this year Bamidbar falls out a week earlier, and Naso is also before Shavuos. Why is this year different from the other years?

Question #2: Why are most of the “Double Parshiyos” clustered together in and around Sefer Vayikra?

Question #3: Why are the Torah’s parshiyos of such disparate length? Some parshiyos are very long — the longest being this week’s Parsha, Naso, which contains 176 pesukim. Yet at the end of the Torah we have four parshiyos that are extremely short – all of them between 30 and 52 pesukim. Why aren’t the parshiyos of similar length?


The Gemara teaches:

Ezra decreed that the Jews should read the curses of the Tochacha in Vayikra before Shavuos and those of Devarim before Rosh Hashanah. Why? In order to end the year together with its curses! [The Gemara then comments:] We well understand why we read the Tochacha of Devarim before Rosh Hashanah because the year is ending, but why is that of Vayikra read before Shavuos. Is Shavuos the beginning of a year? Yes, Shavuos is the beginning of a new year, as the Mishnah explains that the world is judged on Shavuos for its fruit” (Megillah 31b).

However, this Gemara does not seem to explain our practice. There are two Tochachos in the Torah, one in Parshas Bechukosai, the last parsha of sefer Vayikra, and the second in Parshas Ki Savo, but neither of these parshiyos is ever read immediately before Shavuos or Rosh Hashanah. There is always at least one other Shabbos wedged between. In the case of the Tochacha of Parshas Bechukosai, Shavuos occurs usually after the next parsha, Bamidbar, but occasionally after the following parsha, Naso, as it does this year. The reading of the second Tochacha, Ki Savo is never the parsha before Rosh Hashanah. The parsha after it, Netzavim, always has the distinction of being read on the Shabbos immediately before Rosh Hashanah.

Tosafos (ad loc.) explains that the Tochacha should be read two weeks before each “New Year” to allow a buffer week between the Tochacha and the beginning of the year. Thus, Ezra’s decree was that the two Tochachos should be read early enough so that there is another reading following them before the “year” is over. The Levush (Orach Chayim 428:4) explains that without the intervening Shabbos reading as a shield, the Satan could use the Tochacha as a means of prosecuting against us on the judgment day. The intervenient Shabbos when we read a different parsha prevents the Satan from prosecuting, and as a result we can declare: End the year together with its curses!

Divide and Conquer!

We can now explain why the very end of the Torah is divided into such small parshiyos. The Tochacha of Parshas Ki Savo is located towards the end of Sefer Devarim. In order to complete our annual reading of the Torah on Simchas Torah, we want to read this Tochacha at least two weeks before Rosh Hashanah, which means that we must divide the remainder of Sefer Devarim into enough parshiyos for:

(1) A buffer parsha between the Tochacha and Rosh Hashanah.

(2) One or two Shabbosos between Rosh Hashanah and Sukkos.

(3) The Torah reading for Simchas Torah, when we complete the year’s reading, as established by Chazal (Megillah 31a).

To accommodate all this, the end of Devarim is divided into four tiny parshiyos: Netzavim, Vayeileich, Haazinu, and Vezos Haberacha:

Netzavim always becomes the “buffer parsha” read on the Shabbos before Rosh Hashanah. When we need two Shabbos readings between Rosh Hashanah and Sukkos, then Vayeileich is read as a separate parsha on Shabbos Shuva, and Haazinu is read on the Shabbos between Yom Kippur and Sukkos. When there is only one Shabbos between Rosh Hashanah and Sukkos, then Haazinu is read on that Shabbos, which is Shabbos Shuva. And Parshas Haazinu must be short enough to create a parsha after it, Vezos Haberacha, which serves as the reading for Simchas Torah.

Bamidbar is always before Shavuos

Returning back to the Gemara in Megillah, we now understand why the end of Sefer Vayikra always falls at least two Shabbosos before Shavuos. Since the Tochacha is located at the end of Vayikra, Bamidbar must always be read before Shavuos to be a buffer between the Tochacha and the “new year” of the produce of the trees, as explained by the Gemara.

We can now refer back to one of our original questions: Why are most of the “Double Parshiyos” clustered together in and around Sefer Vayikra?

The “Double Parshiyos”

There are seven potential occurrences when we read “double parshiyos“, that is, two consecutive parshiyos are read on one Shabbos as if they are one long parsha. These seven are:

Vayakheil/Pekudei, the last two parshiyos of Sefer Shemos.

Tazria/Metzora, in Sefer Vayikra.

Acharei Mos/Kedoshim, in Sefer Vayikra.

Behar/Bechukosai, in Sefer Vayikra.

Chukas/Balak, in Sefer Bamidbar.

Matos/Masei, the last two parshiyos of Sefer Bamidbar.

Netzavim/Vayeileich, towards the end of Sefer Devarim.

This leads us to a series of interesting questions:

(1) Why are there no doubled parshiyos in Bereishis, nor any for almost the entire length of Sefer Shemos?

(2) Why do we cluster together four doubled parshiyos between the last week of Shemos and Sefer Vayikra?

(3) And lastly, why do we not double any parshiyos at the beginning of Sefer Bamidbar?

With a little more background, we will be able to answer all of these questions.

In this article, I will discuss the reason for the first four of these doubling of the parshiyos.

Leap and Common Years

When Hashem commanded us to create a calendar, He insisted that we use the moon to define the months, and yet keep our year consistent with the seasons, which are dependent on the sun. (The word “month” originally meant “a period of time corresponding to the moon’s cycle,” which is approximately 29 1/2 days, but the use of “month” today in the western calendar is simply a convenient way to divide the year and has nothing to do with the moon’s cycle.)

This mitzvah does not allow us to create either a purely solar calendar, the basis of the common western calendar, which ignores the moon’s changing phases. Nor does it allow us to create a perfectly lunar calendar of twelve lunar months, since this lunar “year” is approximately eleven days shorter than a solar year. If we were to follow a calendar of twelve lunar months every year, our months would not fall out in the same season. Pesach would occur sometimes in the dead of winter and Sukkos in the spring. This is exactly what transpires in the Moslem calendar, which always has exactly twelve lunar months in every year. Moslem months do not fall out in the same season. For example, Ramadan this year falls in the summer, but in a few years will occur in the winter.

The Torah requires that Pesach fall in the spring, yet requires that the months correlate to the cycle of the moon. We fulfill this mitzvah by occasionally adding an extra month to the year – thereby creating 13 month years, which we call “leap years,” to offset the almost 11 day difference between twelve lunar months and a solar year. These extra months keep the Yomim Tovim in their appropriate seasons.

When we add an extra month to the year, we add four and sometimes five Shabbosos to the year, yet we want each calendar year to complete the entire Torah reading on the next Simchas Torah! In order to have a reading for every possible Shabbos, we need to divide the Torah into enough parshiyos so that even the longest year has a parsha for each Shabbos. Since a Jewish leap year may contain 55 Shabbosos, Chumash is divided into a total of 54 parshiyos so that there is always a parsha to read every week. (There are 54 parshiyos, and not 55, because we do not read a consecutive Torah parsha on the Shabbos that occurs during Pesach. Although this is also true on Sukkos, remember that on Simchas Torah we read Parshas Vezos Haberacha, which is one of the 54 parshiyos, so Sukkos does not eliminate the need for a parsha that week.)

To sum up, the reason for dividing the Torah into 54 parshiyos is so that there are enough parshiyos for every Shabbos of the yearly cycle that begins and ends on Simchas Torah. In reality, the need for reading each of the 54 parshiyos on a different Shabbos occurs very rarely – only on leap years when Erev Pesach falls on Shabbos. Only that particular year has 54 Shabbosos that do not coincide with any Yom Tov dates (or more accurately, 53 Shabbosos plus Simchas Torah).

Why do we “double” Parshiyos?

Since most years require less than 54 parshiyos, how do we make sure that we complete the Torah reading for the year on Simchas Torah? The answer is that we combine parshiyos.

In almost every occurrence of a common year, we double the following parshiyos: Tazria/Metzora; Acharei Mos/Kedoshim and Behar/Bechukosai. Why these three sets of parshiyos, all of which are in Sefer Vayikra?

Just as a leap year is created by adding an extra month to Adar shortly before Pesach, the parshiyos are not doubled until the month of Nisan. Thus, we do not add these extra parshiyos until the year is clearly a common year.

At this point we can answer the second question raised above: Why do we “double up” so many parshiyos in Sefer Vayikra?

The answer is that we do not double parshiyos until it is already obvious whether it is a leap or common year, yet we need to read the parshiyos in a way that we complete this process early enough to read Bamidbar before Shavuos. The above-mentioned parshiyos are not read until the beginning of the month of Nisan. Thus, we have a small window between the beginning of Nissan and the end of Sefer Vayikra in which we try to complete all the double parshiyos necessary.

Why did I write above “in almost every occurrence of a common year, we double these parshiyos“? Because there is one instance in which the parshiyos of Behar and Bechukosai are combined in Chutz La’aretz, but they are read on separate weeks in Eretz Yisrael. This occurs in a common year when the eighth day of Pesach, observed only outside Eretz Yisrael, falls on a Shabbos. The communities of the exile read a Yom Tov reading, whereas in Eretz Yisrael communities read Parshas Shemini, the next reading in order. In this instance, the communities of Eretz Yisrael must separate Behar from Bechukosai to avoid the Tochacha from being read the week before Shavuos.


Almost, but not all common years, also combine together the last two parshiyos in Sefer Shemos, Vayakheil/Pekudei. There is one instance of a common year when this does not happen. When Rosh Hashanah and Shemini Atzeres fall on Thursday in a common year that has 355 days, a fairly rare occurence [and one of the instances of a common year when Erev Pesach falls on Shabbos], there is an extra Shabbos between Sukkos and the next Rosh Hashanah, and in this year Vayakheil and Pekudei are read on separate weeks even though it is a common year.

I still have not explained the answer to our first question: Why this year does Bamidbar fall out two weeks before Shavuos, rather than the week immediately before Shavuos.

The Longest Year

The answer is that whenever a leap year falls out with Rosh Hashanah on a Thursday, as it does this year, that year has an extra Shabbos. In this instance, the leap year added five shabbosos to the year. The result of having no double parshiyos in these years between Simchas Torah and Rosh Hashanah is that both Bamidbar and Naso fall before Shavuos.}


We now understand what the printers and calendar makers have known all along: Why and when certain parshiyos are doubled and when not. All this is to guarantee that we have a chance to revisit every part of the Torah in the course of the year, and to celebrate our annual siyum haTorah on Simchas Torah!

Asarah BeTeiveis on Friday?!

In the Yeshiva where I teach, one of my students came to me rather incredulously- "I heard that the Tenth of Teiveis falls on a Friday this year—but I thought that we cannot have fast days on a Friday? I don’t remember a fast ever falling on Friday!"

Although Moshe’s halachic assumption is inaccurate, it is easy to comprehend why he made this mistake. In our current fixed calendar, the only fast day that ever falls on a Friday is Asarah BeTeiveis. And the last time this happened was exactly ten years ago, before he was old enough to fast.

There is another, more sophisticated, basis for Moshe’s question. In a "regular" (kesidrah) year Marcheshvan (usually, but inaccurately called simply "Marcheshvan") contains 29 days and Kislev 30. In such a year, Asarah BeTeiveis always falls on the same day of the week as Rosh Hashanah. And, since Rosh Hashanah cannot fall on a Friday, one might think that Asarah BeTeiveis should not fall on Friday either.

However, our fixed calendar system has fourteen "types of years," seven leap years, and seven common years. Of those fourteen "types of years," four of them result in Asarah BeTeiveis falling on Friday, two of them in a leap year and two in a common year. This is because if Rosh Hashanah falls on Thursday and the year must have a day added (sheleimah), (I explain this concept in a different article which I will be sending in one of the nearcoming weeks) the day added is the 30th of MarMarcheshvan, which postpones Asarah BeTeiveis to a day later in the week – to Friday. In addition, if Rosh Hashanah falls on Shabbos and the year must have a day deleted (chaseirah), the day subtracted is the 30th of Kislev, which moves Asarah BeTeiveis forward one day in the week – again to Friday. Since both of these scenarios can happen in either a normal year or in a leap year, there are four different "years" that result in Asarah BeTeiveis falling on Friday.

This year provides an example. Rosh Hashanah fell on Thursday and the year is sheleimah, meaning that both Marcheshvan and Kislev have 30 days, which avoids Rosh Hashanah from falling next year on Wednesday. But adding the 30th day to Marcheshvan causes Asarah BeTeiveis to fall on Friday. This type of year is referred to as a השג year, theה  standing for Thursday (the fifth day of the week), the day of Rosh Hashanah; the  ש for sheleimah, and the  ג for the day of week that Pesach will fall this year, which is Tuesday, the third day of the week, which result because this is a leap year.

(By the way, the year 5774, which occurs in three years, is also a השג year exactly as this year is, so remember not to throw away your Hebrew calendar at the end of the year; you can reuse it in three years. On the other hand, the molad times will be different, as will the times for zman keriyas shma [which is dependent on the solar calendar], so maybe that is not such a good idea. Good thing for the calendar makers.)

If we plan a bit ahead, we will discover that all four types of years when Asarah BeTeiveis falls on Friday will occur within the next few years. The year 5781 (the end of the secular year 2020), is a common year in which Rosh Hashanah falls on Shabbos. Both Marcheshvan and Kislev are 29 days that year, which results that the last day of Chanukah that year is a Friday, the 3rd of Teiveis, and the fast of Asarah BeTeiveis falls on the following Friday.


If we look ahead to the Hebrew calendar years 5784 and 5785, corresponding roughly to the secular years 2023 through 2025, we discover the fairly unusual situation of having back-to-back years with Asarah BeTeiveis falling on Friday both in 5784 (2023) and in 5785, (when it falls on January 10, 2025), each for a different reason: In 5784, which is a leap year, Rosh Hashanah falls on Shabbos and it is a chaseirah since both Marcheshvan and Kislev have 29 days, thus causing Asarah BeTeiveis to occur one day earlier in the week than Rosh Hashanah – Friday. 5785 is a common year when Rosh Hashanah falls on Thursday and it is a sheleimah when both Marcheshvan and Kislev have 30 days. Of course, I’m sure you noticed that there is no Asarah BeTeiveis in the secular year 2024, but it falls out twice in 2025. I will explain this phenomenon shortly.

A rocket scientist once attempted to explain to me why Asarah BeTeiveis falls occasionally consecutively on Friday. I am going to attempt to explain what he told me. When Rosh Hashanah in a leap year falls on Shabbos, that year cannot be a regular leap year of 384 days, because that would cause the next Rosh Hashanah to fall on Friday, violating the rule of lo adu Rosh, since this would result in Yom Kippur falling on Sunday. To avoid this happening, that year must either be shortened by a day (chaseirah), moving the next Rosh Hashanah forward to Thursday, or by adding a day (sheleimah), pushing the next Rosh Hashanah to Shabbos. Which of these happens is dependent on when the molad of the new moon for the next Rosh Hashanah falls. But if the year is indeed chaseirah, the loss of the day moves Asarah BeTeiveis to Friday, a day earlier in the week than was Rosh Hashanah.

Now then: When the year is made chaseirah (and Rosh Hashanah of the second year falls on Thursday as a result), it sometimes results that the second year requires an extra day to avoid the following year’s molad from falling too early. What has basically transpired is that because one year was shortened by a day, the next year requires a compensation of an additional day. When this happens, both Marcheshvan and Kislev in the second year now have 30 days. This results in Asarah BeTeiveis in the second year being postponed from Thursday to Friday.

If I understood the rocket scientist correctly, the only way this phenomenon of Asarah BeTeiveis falling in two consecutive years on a Friday is when the first year is a leap year that begins on Shabbos that was chaseirah and the second year is a common sheleimah year that begins on Thursday. Every time I have found this on the calendar it has been such a phenomenon, but I take no responsibility for ascertaining that this is the only way this can happen. I make no claim to be a rocket scientist.

What did Teddy Roosevelt and Richard Nixon have uniquely in common?

The last time Asarah BeTeiveis fell in two consecutive years on Fridays was in 5733 (on December 15, 1972, when Richard Nixon was president) and 5734 (on January 4, 1974). Few of those reading this article were fasting the previous time that Asarah BeTeiveis occurred on Friday in back-to-back years since this was on December 20, 1901 and January 9, 1903. Teddy Roosevelt was president, having succeeded to the office when William McKinley succumbed on September 14, 1901, to the wounds inflicted by Leon Frank Czolgosz. According to my research, these were the only two times the phenomenon of Asarah BeTeiveis falling in two consecutive years on Fridays occurred in the Twentieth Century. Is there any significance to the fact that both Roosevelt and Nixon were Republicans? Let us wait eagerly to see who wins the election of 2020 to see who will be president in 2023 and on January 10, 2025, the next back-to-back Asarah BeTeiveis on Friday. Perhaps the Republicans can keep this streak running!

The wait for the next back-to-back Friday Asarah BeTeiveis observances after 2023 and 2025 is not quite as long. Someone planning on good health and longevity can look forward to fasting on two Fridays of Asarah BeTeiveis in the years 5831 (on December 12, 2070) and 5832 (January 1, 2072), providing an auspicious way to celebrate the secular New Year.

By now, you presumably have noted that the secular years 1902 and 1973 both missed having Asarah BeTeiveis, and that so will 2024 and 2071. That a secular year misses Asarah BeTeiveis is not particularly significant. Almost every halachic leap year causes the pushing of Asarah BeTeiveis into the next secular year, and means that Asarah BeTeiveis misses one secular year, and falls out in January and then December of the year following. As a result, seven of nineteen secular years miss out on Asarah BeTeiveis. (Actually, it is slightly less, since about twice a century Asarah BeTeiveis in a leap year falls on December 30 or 31.)


Biblical Source

Although it would appear that the reason no other fast occurs on a Friday is simply a coincidence of the fixed calendar, one early authority contends that observing Asarah BeTeiveis on Friday has a Tanach basis and deep halachic significance. The Avudraham explains that since the verse in Yechezkel (24:2) identifies the Tenth of Teiveis as etzem hayom hazeh, this very day, these words require that Asarah BeTeiveis be observed on the date that it occurs and may not be moved. The Avudraham expressly states that if Asarah BeTeiveis were to fall on Shabbos, we would be required to fast on Shabbos just as we are required to fast when it falls on a Friday. This means that prior to the establishing of our calendar by Hillel Hasheini, whenever Asarah BeTeiveis fell on Shabbos (during the period after the Churban), Klal Yisrael fasted on Shabbos, similar to the fasting we do when Yom Kippur falls on Shabbos! This ruling of the Avudraham seems unusual – particularly, since there is no record in the Gemara of such a halacha.

We can easily understand why the Beis Yosef (Orach Chayim 550) takes strong issue with Avudraham’s approach, and questions why one should treat Asarah BeTeiveis more strictly than any other rabbinically ordained fast. In addition, Avudraham’s position conflicts both with Rashi (Megillah 5a s.v. aval) and the Rambam (Hilchos Taanis 5:5), both of whom mention that when Asarah BeTeiveis occurs on Shabbos, the fast is postponed to Sunday.

Nevertheless, we must understand the conceptual basis why the Avudraham understands Asarah BeTeiveis to be a stricter fast than the others. It would seem that its significance is because it is the beginning of the tragedies that resulted in the churban, a message we should take to heart when we observe this fast, whether or not it occurs on Friday.