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Letter to a Friend: Negotiating Z’manim (Part 1)

November 4, 2014

Dear ***,

With regards to halachic z’manim, the system I recommend you use is actually quite simple. It is the one that is implied in the writings of Maimonides and endorsed by the Vilna Gaon, and the one that figures most prominently in the common calendars you find in synagogues, although in the last few years, the z’manim of the Magen Avraham and Rabbeinu Tam have been displayed more prominently, and more have been advocating subscribing to them as a humra.

First some background: all the basic times are calculated using a day that starts at sunrise and ends at sunset, and the (seasonal) “hours” are defined as one twelfth of that time. If the day has 12 actual hours from sunrise to sunset, then each of those seasonal “hours” is 60 minutes long. Here in Israel, the longest day is 14 hours from sunrise to sunset, and the shortest day is ten hours from sunrise to sunset, so the longest “hour” is one twelfth of 840 minutes, or 70 minutes, and the shortest seasonal “hour” is one twelfth of 600 minutes, or 50 minutes. Most of the halachic times are based on these fluctuating hours. In New York, the day ranges from about 16 to 8 hours, and seasonal “hours” can be even longer or even shorter.

The major points of contention are the following:

According to Rabbeinu Tam, the sunset of the halacha is not the visible sunset. Instead, it is a moment in time after actual sunset, specifically, after the amount of time it takes an ordinary man to walk 3 and 1/4 Roman miles. How long is that? Roman miles were approximately kilometers, and various estimates range between 18 minutes and 24 minutes to actually walk one. The actual time it takes is not so important within the system I recommend. Rabbeinu Tam also says that the stars come out (the halachic nightfall), only after the complete fourth of those Roman miles, which is usually understood as four times 18 minutes, or the 72 minutes after sunset some use to define when the Sabbath ends. Maimonides, and most everybody who lived before Rabbeinu Tam, believed that sunset was sunset, and that it only takes 3/4 of a Roman-mile walk, in his words 18 minutes, for the stars to come out. The Vilna Gaon used the shorter time to walk a mile, and he believed that it only took 3/4 of 18 minutes for the stars to come out, or 13.5 minutes for the stars to come out.

This controversy has many implications. According to Rabbeinu Tam, the calendar day ends almost an hour after Maimonides says it does, and the first time to perform night commandments, like the recitation of sh’ma, or the ending of the Sabbath, are likewise delayed. If the sun rose at 6am and sets at 6pm, Maimonides says the day is out at 6pm, and one may recite the sh’ma or begin working after the sabbath at 6:20pm or so, whereas Rabbeinu Tam would say that that the calendar day only changes at 6:58:30 pm, and one may only recite sh’ma or begin working at 7:12pm. With regards to the beginning of the Sabbath the day before, Maimonides would say that by 6pm, the Sabbath has already started, whereas according to Rabbeinu Tam one may opt to accept it at that time, but only has to observe the Sabbath shortly before 7pm.

Despite its novelty, Rabbeinu Tam’s understanding of sunset and nightfall, when the stars come out, was eventually accepted throughout the Ashkenzaic and Sephardic Diasporas, but not among the Yemenites. The Shulhan Aruch and the R’ma subscribed to Rabbeinu Tam’s opinion, and that’s how the Jewish world practiced it for centuries, but the Vilna Gaon pointed out that “the senses contradict” Rabbeinu Tam’s position. Everyone can see the sunset and notice stars shortly thereafter, but nothing special happens 58 minutes or so after sunset. In places like Israel, it is already completely dark and the vast majority of the stars are out. The Chofetz Chayim advocated using Maimonides’s opinion as described by the Vilna Gaon at least with regards to the strictures it imposes, like accepting the Sabbath earlier, and the Rabbis who lived in Lithuania, who were influenced by the teachings of the Vilna Gaon, also encouraged using the old system, and that’s what took hold in modern day America and Israel. This is the first major controversy.

The second controversy incorporates elements of the first. The Magen Avraham’s manner of calculating seasonal hours is different from the first system described above. The Magen Avraham assumes that to calculate the seasonal hours, the day is defined as the time between aloth hashahar, dawn, a time significantly before sunrise, and Rabbeinu Tam’s nightfall. The traditional understanding of this opinion is that to maintain symmetry, that halachic noon should be when the sun is halfway through its circuit through the sky (which is the exact point halfway between sunrise and sunset) dawn should be 72 minutes before sunrise, just like nightfall is 72 minutes after sunset. Years ago, the Sephardic chief rabbis Mordechai Eliyahu and Ovadiah Yosef suggested their own novel interpretations, but these are only featured in some uncommon calendars. It must be noted that just because an opinion would believe that dawn is 72 minutes or so before sunrise and that nightfall is 72 minutes after sunset, like the Shulhan Aruch did, it does not necessarily mean that the hours of the day are not calculated from sunrise to sunset. (Note that when I say 72 minutes, I mean four times an 18-minute mile. If it takes 22.5 minutes or 24 minutes to walk a mile, then the time interval could be as much as 90 minutes or so, and there are opinions like that, but all of them are assuming like Rabbeinu Tam did, so they are largely irrelevant for this discussion.) When the the calendar makers calculate Magen Avraham “hours,” say, when sunrise to sunset is exactly 12 hours, which is 720 minutes, they add another 144 minutes to the day, for a total of 864 minutes, or 72 minutes per “hour”.

Now a practical case: on such a day, Maimonides would say that one has from dawn until 9am to read the sh’ma: the time from dawn to sunrise, i.e. from dawn until 6am, dos not count toward those three hours he has to read sh’ma. Those three hours are only counted once the sun rises, and in practice he has a window of like four hours to say sh’ma. Likewise for prayer, assuming one has four hours to finish Shaharith: One really has well over four hours to so, and the time ends at 10am. However, the Magen Avraham’s system starts the three hours at dawn, 72 minutes before sunrise. Those three hours are for a total of (3×72 minutes=) 216 minutes, leaving only 144 minutes after sunrise. 144 minutes is 2 hours and 22 minutes, meaning the final time for reciting Sh’ma is at 8:22am, 48 minutes before the Vilna Gaon’s last time for sh’ma. (The end of the fourth hour would be 9:34 am). You see that following the Magen Avraham in this regard is a little more difficult, but that should not be an argument against following his opinion, and the best argument FOR following his opinion is this: If one has three hours of the day to recite sh’ma, and being that we hold that the halachic day starts at dawn, those three hours should start at dawn.

However, this could not have been the case any time before the modern era. When the ancients spoke of hours, they could only count them during the daytime, and only when the sun was shining. Any time between sunset and sunrise was counted in much less precise units, such as ashmoroth, “watches,” each of a third of the night. This is true for the entire Mishna and Talmud, because sundials only work by day. When our sages discussed hours, it could only have been when hours could be detected, and therefore, even though the day may start at dawn, the count of hours can only start at sunrise and must end at sunset.

You can now understand why the authorities have taken sides in these two issues. The first because sunset should be sunset, and the second because hours can only be counted when the sun is shining.

(Continued here.)


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  1. Maurice permalink

    Hey Avi,
    Nicely done. I only mention it b/c I know you like being precise. In your example of the day the Gr”a’s timing would be 38 minutes, not 48 later than M”A.
    Much love,

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  1. Letter to A Friend: Negotiating Z’manim (Part 2) | Avraham Ben Yehuda

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