After understanding why it is that we keep a double-standard year, and what was involved in creating the Jewish calendar, let’s take a step back for a moment in order to understand one of the most interesting issues of the Jewish world today: why keep a two-day Yom Tov?
In light of the ease of travel that we have, today, relative to yesteryear, crossing international date-lines, leaving Israel after Yom Tov only to arrive in, say, America during the second day of Yom Tov, or even leaving one country after Shabbos to arrive in another ON Shabbos are all feasible possibilities. What do we do in these situations? Should we put ourselves into them? All of these are serious questions and a competent halachik authority should be consulted if there is a pressing need to enter them.
Of all of the above issues the easiest to address is that of the two-day (and sometimes three-day, such as this year) Yom Tov. Why do we have to keep them today? Why is Rosh haShanna different in this regard? Why is Yom Kippur only one day?
The answer to this takes us back to the issue that we elaborated on in the previous blog, Jewish Time 4, the essential Kiddush haChodesh.
During Torah/Prophet/Mishna/Gemara times the way that the Jewish month was establishes was solely based on the authority of the Sanhedrin. This is true for as long as the Sanhedrin existed as the governing body of all halacha in Israel, whether they were sitting in their “proper” home, in Lishkat haGazit (the Hewn Stone Chamber) in the Beis haMikdash (the Holy Temple in Jerusalem), or whether they were in any of the other 9 places to which the Sanhedrin moved to after leaving their proper place. This practice continued for an indeterminate amount of time after the Mishna period, during which time there still existed a functioning Sanhedrin. During the entire Mishna period the center of all Judaism and of all Torah was Israel, even though the actual “home” travelled around the country.
Again, the procedure for Kiddush haChodesh was always the same: at the correct approximate time witnesses would come to testify in front of the Beis Din of the Sanhedrin, which was responsible for establishing the beginning of the new month. Their family history (to insure they were kosher and reliable witnesses) and testimony was checked and verified, after which the Rosh Beit haDin would establish the new month by proclamation “Mekudash! Mekudash!”. Once this was done – today became the 1st of the new month for all matters: festivals, bar/bat-mitzvah’s and more.
Obviously, this was a very difficult thing for calendar makers, because you just can’t make a proper monthly planner when the 1st of the month is up to the Sanhedrin to establish. Meheirah yiboneh Beis haMikdash (the Beis haMikdash should be speedily rebuilt (AMEN!)) and we’ll deal with the problem then. Don’t worry! There WILL be an app for that!
However, calendars aside it was also very difficult simply because Israel was not the only home of the Jewish people. During the times of the Mishna there was still a significant Jewish community living in Babylonia, in Rome, and in many other places as well (depending upon the time period as the Jewish people slowly spread out). How were they supposed to know when the new month began?
Realistically, they couldn’t. It’s not because we lacked the ingenuity, the Mishna in Tractate Rosh haShanna (Chapt. 2, Mish. 4) describes for us in detail that at one point in time an elaborate bonfire system was set up which allowed the news to be quickly and easily spread. However, because of our antagonists of the time, the Sadducees, that system came to a screeching halt and needed to be replaced with the only other “official” system available at the time: the “town crier”. Called “shluchim” (=sent people) in the Mishna the only way to relay the news of the declaration of the new month was by sending an official messenger on horseback all the way to Babylon to relay the news. This was a difficult process and would take several weeks to achieve. As a result, a significant amount of the time there was no way to know during the months of Nissan and Tishrei on which of the two possible days (day 30 or 31 from the last new month) this month was going to begin, and conversely, when the 15th of these months came around they didn’t know if today was (for example) the first day of Pesach or if it was tomorrow. As a result, because the performance of melachos (the 39 categories of creative acts forbidden on Shabbos, of which all food-related melachos are permitted on Yom Tov with certain stipulations (yes, the halachos must be learned)) was forbidden and it wasn’t known whether the davening (prayers) of Yom Tov were to be said today or tomorrow, as well. The result was that they treated both days as if they were both Yom Tov, both at the beginning and the end of these two festivals, and for the first two days of the festival of Shavuot. Any positive mitzvos which were commanded to do on Yom Tov were kept and all negative mitzvos were refrained from. Therefore, in chutz la’aretz (outside of the land of Israel) they would sit in the sukkah on day eight, which was a possible day-seven assuming that the second possible day of Rosh Chodesh was the new moon, and they would refrain from putting on tefillin on the ninth day, assuming it was possibly the eighth day. During all of the possible days of “Yom Tov” the festival prayers were also recited.
Now, the above is all nice-and-good when it comes to the general festivals. However, when it comes to the topic of Yom Kippur it becomes an entirely different issue. After all: how can a Jew possibly get by without eating?
If you think about it, (Tisha b’Av aside), there isn’t a single Jewish festival which isn’t celebrated with food! Even Yom Kippur is celebrated with food! It’s just that we do it on the day before.
In any case: Jews without food is not just funny. It’s potentially life-threatening. It was therefore decided that despite the quandary in which we found ourselves concerning the festivals, we couldn’t take that road as far as Yom Kippur was concerned. It is just not possible for a Jew to fast for two entire days straight without eating and drinking. (Especially in a time before air conditioning!) Therefore, all Jews everywhere kept only one day of Yom Kippur.
Rosh haShanna, comparatively, is completely different than all of the other festivals, and that is because it, itself, falls out on Rosh Chodesh. In light of this, in all places and in all times, there was only one thing to do when it came to Rosh haShanna, and that is to keep two days. After all, if the eidim (the witnesses) don’t come on the first day of Rosh haShanna to testify that they saw the new moon then the proclamation of “Mekudash” wasn’t made, and therefore the second day of Rosh haShanna became, de facto, the first day of the month of Tishrei.
Concerning all of the above, although manageable, it became quite difficult to adjust to life. However, when we stopped doing Kiddush haChodesh based on the testimony/Beis Din system one would think that life would now become easier! After all, once we have switched to a mathematical system, in which we can “predict” already well ahead of time when the next 50,000 (or so) Rosh Chodashim are going to be – so why are we still keeping the two days? Because of a safek (doubt) as to which day is Rosh Chodesh? We don’t have a doubt anymore!
This isn’t a new question. In fact, the Gemara in Tractate Beitzah asks this question:
אתמר “שני ימים טובים של גליות רב אמר ונולדה בזה מותרת בזה ורב אסי אמר נולדה בזה אסורה בזה”. לימא קא סבר רב אסי קדושה אחת היא? והא רב אסי מבדיל מיומא טבא לחבריה! רב אסי ספוקי מספקא ליה ועביד הכא לחומרא והכא לחומרא. אמר ר’ זירא “כותיה דרב אסי מסתברא, דהאידנא ידעינן בקביעא דירחא וקא עבדינן תרי יומי”. אמר אביי “כותיה דרב מסתברא, דתנן ‘בראשונה היו משיאין משואות. משקלקלו הכותים התקינו שיהו שלוחין יוצאין’, ואילו בטלו כותים עבדינן חד יומא. והיכא דמטו שלוחין עבדינן חד יומא. והשתא דידעינן בקביעא דירחא מאי טעמא עבדינן תרי יומי? משום דשלחו מתם ‘הזהרו במנהג אבותיכם בידיכם!’, זמנין דגזרו המלכות גזרה ואתי לאקלקולי.
The Gemara presents an argument between Rabbi Zeira and Abaye in how we are to understand the argument of the great sages of the first generation of the Gemara period, Rav and Rav Assi. Both Rabbi Zeira and Abaye try and understand the words of these greats in light of the fact that in their days they were “familiar with the establishment of the moon”, (ידעינן בקביעא דירחא), which means that they knew the mathematical formulae required to establish the new moon because the Sanhedrin was no longer doing that which was done throughout time: proclaiming the new moon. The problem being: why do we still keep two days? Rabbi Zeira’s answer was that both days were made into a “single” day as far as their kedusha is concerned, and therefore any stringencies that apply to day one also applies to day two, for example an egg laid on day one is also forbidden on day two. Abaye’s opinion, however, is that in reality no such geziera (enactment) of Beis Din was ever made. Therefore, both days are considered separate and were kept only out of doubt as to which one was THE day. So today, when we no longer have such a doubt, why is it that we still keep two days? To which Abaye answers that a message was sent from “there” (a reference to the Great Beis Din in the land of Israel) “Be wary (to keep) the minhag (custom) of your forefathers in your hand (i.e. keep doing what your fathers did)” despite that it is no longer necessary. The reason given is quite simple: who is to say that you will be able to keep doing what you’re doing? Who’s to say that the foreign governments who rule over you won’t be oppressive and succeed in repressing you, mess up your calculations and cause them to be forgotten. Then what do you do? The answer: keep doing what your parents did and you won’t mess up. However, this reasoning is even more far-reaching and we’ll explain in the summary.
It is for this reason that, to this day outside of the land of Israel all festivals are kept for two-days.
To sum up:
Rosh haShanna was always a safek everywhere. Because of the doubts as to which day would be established and become THE Rosh Chodesh it was established at some point in time that both days of Rosh haShanna were to be considered one day in all respects, “one kedusha”. Even to this day everywhere, even in the land of Israel, it is kept as two days both because it is “one kedusha” AND because of the reasoning “be careful with the minhag of your parents in your hand”, keep doing what your parents did and don’t rely solely on the math. Therefore, Rosh haShanna is a two-day Yom Tov.
Yom Kippur, due to the difficulty and likely danger that would come from fasting for two days straight, was never kept as a two-day Yom Tov everywhere. There is no reason for us to change that today, especially in light of the fact that we are familiar with the lunar cycles and we know when Rosh Chodesh is.
Concerning all other festivals, the minhag of Eretz Yisroel has always been to keep one-day and in chutz la’aretz it has always been to keep two days. Le’halacha this is because of the reasoning of Abaye, who said that it was a special enactment from the Great Beis Din in Israel that proclaimed that this is how we are to continue to behave until the re-establishment of the Sanhedrin. May it be speedily in our times!
 See Tractate Rosh haShanna 31a for more detail on this
 Concerning this issue there is a bit of an argument among the sages, ob”m, as to whether or not the proclamation of “Mekudash” still needs to be made or whether it becomes mekudash without our help. See Rosh haShanna 2:8