Tuesday, January 31, 2012

Wanted: An Experimental Yeshiva

No, that title is not meant the way it may sound.

My father likes to note Rashi to this week's parshah (Shemot 16:14), in which he offers a science experiment: If one fills an eggshell with dew, seal her and leave her in the sun, she will rise independently into the air. Based on the pronouns, it certainly seems that Rashi meant the shell would ascend, presumably as a function of the dew's ascension.

Here is the Rashi:
כשהחמה זורחת עולה הטל שעל המן לקראת החמה, כדרך טל עולה לקראת החמה, אף אם תמלא שפופרת של ביצה טל, ותסתום את פיה ותניחה בחמה, היא עולה מאליה באויר. ורבותינו דרשו שהטל עולה מן הארץ באויר, וכעלות שכבת הטל נתגלה המן וראו והנה על פני המדבר וגו':
[For an interesting aside on Rashi's language, see here.]

I was thinking about this the other day, when contemplating experiments yeshivot could perform in order to understand gemara better. Many passages of gemara rely on familiarity with physical realities we don't normally encounter, and these experiments would help us understand what the Rabbis were discussing.

To put it differently: Imagine learning Maseches Succah without ever having seen an esrog before, or Maseches Chullin without the benefit of seeing a cow, or the various modern picture books which illustrate the innards of a cow. It's inconceivable – but that's the way our yeshiva students learn much of the Talmud, including segments which relate to daily ritual. So here are some experiments they could conduct, which would help:

For Maseches Berachos and the discussion of the earliest time for Shma – Go to a place far from urban light pollution, on a clear night, 90 minutes before sunrise, and watch the morning lighten. Set up black, green, blue and white strips of paper, and see when you can discern the difference between them. Time how long the sun takes to cross the horizon.

For Maseches Shabbos and the thresholds of cooking (Maachal Ben Derusai) – Cook a piece of meat 1/3 of the recommended time and test its edibility. Do the same at 1/2 of the recommended time.

For Maseches Pesachim and the discussion of which plants become chametz and which do not – Get wheat and barley kernels, as well as grains of rice, grind them up and expose them to water. Watch what happens, and how long it takes.

For Maseches Beitzah and discussions about the muktzeh status of fruit that has been left to dry, as well as for various halachic discussions which revolve around dried figs – Leave grapes and figs in the sun, and monitor the process as they dry out. Test them for edibility at various stages.

For Maseches Rosh HaShanah and discussions about testimony regarding the sighting of the new moon - Take a field trip on a clear night at the end and start of the lunar month and make observations of the shape and location of the moon.

For Maseches Bava Kama and discussions about tort law and harm caused when items fall into a pit which is ten tefach deep - Dig a pit that deep and experiment dropping various items in.

For Maseches Niddah and the discussion of kesamim (stains which may be blood, but might not be) – Crush lice and examine the quantity and color of the blood produced.

There is much more to do, of course; this is just a start. Some may be more useful, some of more narrow benefit, but this might make the learning experience more 'real' for some students, as well as help them grasp the concepts involved. Some of this is tongue-in-cheek, but not all of it.


  1. Many Yeshivot in Israel do a lot of hands-on stuff, although there is always room for new ideas.

    My son's Yehiva (Bnei Akiva Yeshiva in Modi'in) has hands-on Tanach program for the advanced students; every month they finish a Sefer in tenach Bkiyut, and then get on a bus to visit a location connected to the sefer they read (the joke in the Yeshiva is that they're waiting for Daniel or Megillat Ester so that they can go to Iran).

    But you're ideas are all great suggestions, could also be good programs for summer camps.

  2. Many years ago, Mesivta Ohr Torah in an old mansion in Riverdale... we did most of those things. The yeshiva was run by R' Riskin, the principal was R' Baruch Chait, and our primary source of hands-on experiences was R' CO Chait.

    Then R' Riskin had this crazy dream about starting a city in Judea (yeah, like that would ever happen), left the school, and it lasted a few more years after going mainstream and moving to a normal school building in Queens.

  3. This comment has been removed by the author.

  4. Some good ideas here, but wouldn't recommend the one about checking for edibility of meat at 1/3 the cooking time. If by checking you mean simply cutting open the meat to see if there is still raw looking flesh or blood visible on the inside would be one thing. But if by edibility you mean actually ingesting a piece of the meat to see if it's edible, that's playing around with possible food poisoning, since undercooked meat is an excellent source of bacteria/organisms that can cause intestinal problems.

  5. I don't think rashi did the experiment. i noticed this in tosphot also in which he gives an excellent way of calculating "pi" but you can see that he never did the experiment. I think the value of experiments had to wait until Galileo and roger bacon.
    I think during the Middle ages texts were considered evidence along with rigorous reasoning about the texts.
    Maybe that is way the thinkers of that period were much more rigorous logical thinkers than any later generations.

  6. Steg (dos iz nit der šteg)January 31, 2012 at 5:34 PM

    "Halakha Lab"!

  7. Michael-
    Cool; yes, the touring component is very important as well.

    R' Micha-
    I knew of the school, but I never knew the background. Too bad.


    Adam Zur-
    The gemara seems to value practical knowledge (as in שעיר החורי and Rabban Gamliel's astronomical charts), so I tend to doubt this.


  8. More to the point than my previous post... the school produced an abnormally high number of people in kelei qodesh. (Or who otherwise work for Jewish causes, if you do not consider things like Birthright or a morning radio show to be "kelei qodesh".) I just visited my sons in Israel.

    IOW, what we had wasn't only creative and special, it was effective. It inspired.

  9. Steg (dos iz nit der šteg)February 1, 2012 at 10:39 AM

    My ḥebrusa and i thought about Halakha Lab when we were learning Issur v-Hetter -- only problem is that some of the experiments involving basar b-ḥalav would actually be asur, so you'd have to use substitutes. Maybe water with different colors and [parva] flavorings in order to test ta‘am and bittul.

  10. Here's the problem. If we did the test and discovered that food is only edible after it's 2/3 cooked, would we pasken that way? And what if we found that taam is indeed not noticeable if it's less than 1/40? Or that lice are not spontaneously generated? So far the trend has been that experimentation has not generally confirmed the assumptions behind halacha; further validation of those assumptions will just create further questions that we'll need to respond to or ignore or explain away. Maybe I'm just at a cynical stage of my religious development, but I don't have a lot of confidence that empirical evidence will confirm a lot of the assumptions behind halacha.

  11. i can brag that i did the experiment with rabbainu tam. I decided a medium star is th medium of all visible stars (not the medium of the large stars that come out after 10 minutes) so it made sense to me that the only way to determine a medium star is to wait until all stars come out and then to pick three of what look medium. then to wait until the next night and wait to see when those exact same starts come out. To do this you need to know the constellations and the summer sky i don't know very well so i had to do this in the m\winter. Rabbi Yehuda in the gemara in peshachim is talking about the sky in the land of Israel so i had to do this experiment there. and he is talking about a place where there are no city lights so i had to do this far from any city. I discovered medium starts come out at about 45 minutes to one hour close to what rabbainu tam said. but i discovered further what the 72 minutes is about in the gemara shabat and why it really is exactly 72 minutes It really is about the sky as you can see in the gemara in shabat. I still have not figured out any way to settle the opinion of the Gra. If the gra would be right you would have t see a medium star right at the first skia and another a few minutes later and then three after 13 to 18 minutes. non of this happens in Israel--anywhere (As rav Montag the rosh yeshiva in netivot told me.)i can brag that I did the experiment with Rabbainu Tam. I decided a medium star is th medium of all visible stars (not the medium of the large stars that come out after 10 minutes--as the gemara itself says). So it made sense to me that the only way to determine a medium star is to wait until "all" stars come out and then to pick three of what looks like "medium." Then to wait until the next night and wait to see when those exact same stars come out. To do this you need to know the constellations and the summer sky I don't know at all, so I had to do this in the winter (as a youth i used to study the sky in the winter and did photographic astronomy. I made pictures of the starts and the moon by delayed exposure of a camera attacked to a telescope.u). Rabbi Yehuda in the Gemara in peshachim is talking about the sky in the land of Israel so i had to do this experiment there. and he is talking about a place where there are no city lights so i had to do this far from any city. I discovered medium starts come out at about 45 minutes to one hour close to what rabbainu tam said. but i discovered further what the 72 minutes is about in the gemara shabat and why it really is exactly 72 minutes It really is about the sky as you can see in the gemara in shabat. I still have not figured out any way to settle the opinion of the Gra. If the gra would be right you would have t see a medium star right at the first skia and another a few minutes later and then three after 13 to 18 minutes. non of this happens in Israel--anywhere (As rav Montag the rosh yeshiva in netivot told me.)

  12. R' Yechiel Michel Tukachinsky, in a booklet titled "Bein haShemashos", said that in practice in EY it takes about 22 min after sunset before the stars could be seen. R' Yehudah Levi, "Zemanei haYom", says that a trained eye of average natural acuity can see them in 15 min. The Gra explicitly says his mil is 22-1/2 min, so RYL's number is in the right range. BTW, among the Gra's arguments is that Rabbeinu Tam's shitah is far from the experimental data.

    More importantly: it's not the Gra's position. The Gra was trying (mostly successfully, as it turned out) to restore the position of the geonim, in particular, R' Sherira and R' Hai. The Rambam, Ritva, Rashba and (of course) Rabbeinu Tam actually advocated and got Kelal Yisrael to switch from an earlier opinion.

    To me, this argues that in EY and Bavel (same latitudes), the two opinions must be describing something similar, and it's only after we left Bavel that the two models diverge. I don't have it worked out how that's possible. It would involve the range of values for the mil (18 - 22.5 min) and the machloqes about whether the time is a fixed number of minutes, or the number of degrees the sun would be below the horizon on the equinox in EY after those minutes.

  13. Micha-
    What else did the school do that might have contributed to this result? Or was it overall atmosphere? Or is this really about the types of families which chose to send their kids there? Or...?

    With enough creativity, substitutes may be found, certainly.

    If that happens, then we will have learned important lessons about the halachic process.

    Adam, Micha-
    Fascinating... and, to me, worthy of research.

  14. Micha i would love to say that the gra was right. But i cant. the gra uses a criteria that works against him. he writes "the senses prove". he meant that the senses prove that the sun dos not go above the earth at night. But simply using the senses as proof does not work. Besides my own observations the official time for night when all star are out is 90 minutes. And this corresponds exactly to was i saw that medium starts come of at 45 to 50 minutes. plus besides the starts i also saw exactly what the gemara in shabat was talking about concerning the horizon. plus this is a debate among the geonim.

    here is the little excerpt from my little booklet on bava metzia (at the end of the booklet i put in little interesting questions like this just to add to the fun.)

    ) בעניין שקיעה של רבינו תם. רוב ראשונים פוסקים כמו ר''ת. אני מתקשה להבין את הגר''א. השתדלתי למצוא אופן שהגר''א יכול להיות בהתאם עם הגמרא בשבת, ועדיין לא מצאתי אופן כזה. אם הגר''א היה צודק, היה בהכרח לראות כוכב בינוני אחד בשקיעה הראשונה, ואחר כך עוד אחד בתוך כמה דקות.
    זה כדי ששקיעה תיחשב להיות בין השמשות. וזה רק אחרי שכבר קודם השקיעה, היינו צריכים לראות שלשה כוכבים גדולים. ואי אפשר לדעת את הממוצע של קבוצה מסוימת אלא אם כן יודעים את כל הדברים שיש בקבוצה, ואי אפשר לדעת מה זה כוכב בינוני אלא אם כן קודם זה רואים את כל הכוכבים (שאפשר לראות אותם בלי משקפת), ואז אפשר לדעת מה זה "בינוני". ואז צריכים לבחור כמה כוכבים בינוניים, ולראות מתי הם יוצאים בליל המחרת. אני עשיתי את זה, ולפי מה שראיתי, לא יוצאים כוכבים בינוניים עד בערך ארבעים וחמש דקות אחר השקיעה בארץ ישראל.
    תוספות רי''ד בשבת מפרש רבינו תם גם לשיטת חכמי יוון שנצחו חכמי ישראל כאמור בגמרא בפסחים- והם אמרו שאין מסדרון (פרוזדור) שהשמש נכנס בו בשקיעה. (הגם שלפי מושגים של היום דבר כזה לא יכול להיות--- שחכמי יוון ינצחו את חכמי ישראל.) רב נטרונאי גאון אוחז את השיטה של הגר''א. אבל רב סעדיה גאון אוחז את השיטה של רבינו תם (מצוטט באבן עזרא שמות י''ב פסוק ד').

    sorry about the Hebrew--i never learned Hebrew grammar so my Hebrew is a mix of old and modern with some street Hebrew thrown in.

  15. TRH:

    Another advantage of "Ohr Torah" (its Riverdale incarnation), a/k/a MHS, was that there was a strict ceiling on population. The school wouldn't exceed 80 guys; more individual attention.

    But it probably also gave them the power to preselect candidates. If the selection process is any good the high results might be due to having a disproportionate number of students predisposed to religious leadership before they even got started.


    I can't argue you out of believing your own senses. But I did point out that RYMT and RYL both did the experiment as well, and their answers were wildly different than yours (but in line with each others'). Leaving us third parties kinds of in the dark as to what to believe.

  16. OK I can tell you what happens. You sit there in Israel on some mountain top. You wait some time. after the first sunset some starts come out after about 15 minutes. then you wait some more and more stars appear. these second stars are less bright than the first and at first glance might be called medium. the problem with this is that if i have lets say ten numbers in my head and i tell you nine of them can you tell me the medium number? No why not? because you cant know the medium until you have the whole group. this is the reason why you cant know what a medium star is to the average naked eye until you see all the star that are viable to the average naked eye. And after this then you need to check out when that group of true medium stars come out. these come out after about 45 to fifty minutes.

  17. i once spoke with the rosh yeshiva of maalot hatorah (har nof) about this issue. Even though he is a person that i admit is a scholar still he thought that after the first level of stars comes out then the second level is called medium even though they are not really medium compared with all the stars visible to the average human eye (if you wait until a an hour the stars that look medium fifteen minutes after shkika look gigantic an hour later.) the rosh yeshiva in netivot rav montag when i discussed this with him told me that he thought that my reasoning was what was behind the pesak of the chaozon ish to wait until 50 minutes. These are people that even i have to agree that they know how to learn.--so there it is.

  18. Adam Zur, I respect your commitment to investigation, but the experiment you propose may no longer be possible. The air in most places today is less clear than it was a thousand or two thousand years ago, and light pollution means that we are less able to see dim stars.

    I suggest that a better technique would be to find references to "bright" and "medium" stars in halachic works, and use an astronomical atlas (which has stars classified by levels of brightness) to find out what these terms mean. Then you can use a formula to estimate at what time these stars would have been visible to someone in Bavel or wherever.

  19. the problem there is that in places where the sages make reference to stars like "chima" there is debate which star they mean. and i want to mention my problem with the Gra is not just the stars but that whole sugia in shabat about the way the horizon looks after shkia. This also did not work according to the Gra but from what I could tell in Israel it worked with Rabbainu Tam. What happens in Israel is that after the sun sets the sky does not change much except for getting slowly darker. But then at exactly one hour something dramatic happens. There is like a kipa over the area where the sun sank. (This would be at Rabainu Tam's ben hashemashot). Then this kipa sinks and disappears at exactly 72 minutes. You can time your watch to this. I did and every time it came out to exactly 72 minutes.
    This could fit with rabbu tam. Now that gemar in shabat might have been like the gra if the gemara had concluded that the reference in the braita was the east. This maybe could work to the gra. But the Gemara itself concludes that it is referring to the west. So I just don't know what to say about this Gra. I guess it must be that the Gra was assuming that rabbainu tam was based on the idea of the sun going about the sky at night. Once it was clear that this is not the case ("the senses prove" in his words) Then he must have felt that the whole basis for rabbainu tam disappeared. That is the only way i can understand the Gra. The problem with this is that rabbu tam is not dependent on where the sun goes at night but rather on a contradiction between statements of rabbi yehuda.

  20. RAZ,

    To repeat my problem... I can't expect to argue you out of the evidence of your own senses. But look at it from my perspective, as a third party.

    The Geonim, who lived in a similar latitude to EY, held the way the Gra later championed. We have written teshuvos from R' Sherira and R' Hai Gaon, writing in Pumbedisa -- which today is called Falluja, Iraq. To compare, Y-m is at 31 deg 47' N, Falluja is at 33 deg 21' N. Whereas R' Tam's hometown of Troyes, France is at 48 deg 19' N and the Gra's Vilna, 54 deg 40' N.

    I find it hard to believe that the geonim and the Jewish people when the majority lived in the Middle East didn't have a plausible definition of tzeis, when the definition was given WRT a nearby area (EY).

    Second, the Gra was no stranger to math and science, even if he couldn't have done the experiment himself. He raises the astronomical implausibility of R' Tam's et al's opinion as one of his reasons for recommending reversion to the position of the geonim. If he were silent, it would be one thing; but it would seem R' Tam's shitah doesn't fit the spherical trig.

    I also am faced with conflicting experimental results. I can't ask R' Tukachinksy and R' Levi how they conducted their experiments, to see why their results differed from your own. But given my previous 2 observations (that the geonim's tzeis had to work for an area very similar to EY and that the Gra had scientific theory against the rishonim's position) I'm inclined to believe that what they measured was more meaningful to our conversation than how your experiment was conducted.

  21. 1)Saadia geon holds by rabainu tam. רב סעדיה גאון אוחז את השיטה של רבינו
    תם (מצוטט באבן עזרא שמות י''ב פסוק ד

  22. Here is the IE's quote of RSG:

    אמר הגאון רב סעדיה ז"ל, מדת מזבח העולה חמש אמות אורך, וחמש אמות רוחב. ובמדה הזאת לא יעמדו כי אם כהנים מעטים, שהם זורקים דמי הפסחים קודם שיקרשו. והנה בימי יאשיהו (דהי"ב לה, א), שהיו ישראל מועטים לא יכלו הכהנים לזרוק דמי הפסחים והשלמים ששחטו לזרקם לשעה ושליש שעה, ואף כי בהיות כל השבטים בארצם. . והנה היתה קבלה, שיחלו לשחוט מהרגע שיתברר לאדם כי השמש נטה לצד מערב. והזכיר הכתוב בין הערבים, שרוב הפסחים היו אז נשחטים שם, והוא סוף הזמן שלא יעבור עד עריבת אור השמש:

    Is RSG not talking about 80 minutes before sunset? The Pesach had to be slaughtered during the day; this discussion of how to define "bein ha'arabayim" has nothing to do with bein hashemashos.

    The normal understanding of the sugya (IOW, how it's normally taught in secondary sources) is that the rishonim (Rambam, Rabbeinu Ram, Rashba and Ritva) overturned the commonly accepted practice from the geonim. That in itself raises interesting questions about how halakhah works.

  23. Micha. Thank you for looking it up. I showed this Saadia Geon to rav Montag in Netiovot. (part of that yeshiva was learning bava metzi so i printed up my little booklet on bava metzia which had this little paragraph about rabbainu tam at the end. some people in the yeshiva noticed it so somehow i got into a discussion with him about this subject. he also at first said that the Gra is the opinion of the Geonim). And he had the same reaction as you until I showed him the next paragraph. Then he agreed that Saadia Geon holds by Rabainu Tam. Many years ago I had the same experience with Rav Eliyahu Zilverman in the old city who is the head of the yeshiva of the Gra (Aderet Eliyahu). I came in for a quick shalot seudot about 30 minutes after shkiya (to his father in law's house) and Rav Zilverman was there. This started a whole discussion about Rabbainu Tam in which I also had to dig up this Saadia Geon. (It took me a very long time to find it). After he say the next paragraph he also agreed that the only way to understand it is like Rabbainu Tam.
    That was not the end of the discussion. (My approach is in which most basic rishonim are legitimate. And he knows this. So I think he only brought up this subject because it was at some one else's home--not at his own home--where i usually went for the third meal.

  24. 1- There is no way RSG or the IE meant 80 minutes after sheqiah, because one may only shecht a qorban Pesach (or any other qorban) before sheqiah. Similarly zeriqas hadam. This is mentioned in numerous places in shas, eg Zecvachim 56a.

    2- Even if that were what was meant, it would be worse for your case. 1-1/3 hours isn't 1-1/5. And if he meant to be talking about tzeis, RSG's not using the word is very odd. If he were talking about 1-1/3 hours after sheqiah, I would argue it's indication that such a time is NOT what he considers tzeis.

    3- You mention "the next paragraph". So I went back to the Bar Ilan CD web site. (What, you thought I typed all that?) This comment is at the end of pasuq 6. The IE's comment on "al shetei hamezuzos" doesn't refer to time nor R' Saadia.

    responsa.co.il only has one hit when you search for "לשעה ושליש שעה", this IE.

    So, I need a more specific reference to the "next paragraph" you are pointing our attention to.

  25. micha.. You are right about the 80 minutes. I really am not in this sugia right now but i do remember the only options for rabbainu tam that i recall off hand were 72, 90, 96 and maybe 2 hours for the disciple of rabainu tam who goes by 5 mil (eliezer from mitz) so 80 is a mystery to me. By the words:"the next paragraph" I meant the end the whole piece of Ibn Ezra on that posuk. I really don't remember it but I do remember that when I showed it to Rav Montag and to Rav Zilverman (who I admit both know how to learn) when they saw the fist paragraph (that you quoted) they both said that is not a proof. And then I mentioned that the proof was at the very end of the Ibn Ezra. They looked at that and then agreed. If your suggestion is that the end of the Ibn Ezra is not about Saadia Geon then you would be right. The proof lies in the idea that the Ibn Ezra is explaining Saaadi Geon.

  26. ok i just looked at the paragraph you quoted and i see that the 80 minutes is the end of time one can bring the sacrifice. that means that is the beginning of bein hashemashot to Saadia geon if you go by the beginning of the night to be 96 minutes. (the length of bein hashemashot is in general 1 1/4 of a mil.) I saadia would be taking a mil to be 24 minutes. This makes perfect sense in the gemara in peshachim but so does 72 minutes depending on where you start your counting. at any rate i choose the 72 minutes for the reason that the astronomical night when scientist say that all the stars that are viable to the naked eye are out is 90 minutes. so obviously i cant say that that is when three medium stars come out. (though i admit that when i was up in very cold mountain areas in America it did seem to me that i could see a lot more starts a few hours after sunset than just at 90 minutes. But at any rate you can see how that reb moshe and the chazon ish were going with the idea of circa 50 minutes.

  27. (Just to play math games... If R' Saadia were talking degrees and after sunset... 72 min at the equinox might be appx 80 min come Pesach.)

    Here's the IE on 12:6 in full:
    (ו) והיה לכם למשמרת שישמרנו כל אחד בביתו.

    בין הערבים - מלה קשה. ורבינו שלמה אמר, כי רגע נטות השמש מחצי היום לצד מערב. ולא נתן טעם למה ערבים - שנים. והנה כתוב, ובהעלות אהרן את הנרות בין הערבים (שמות ל, ח), ואין ספק כי בשקוע השמש ידליק את הנרות. וכאשר חפשנו זאת המלה, מצאנו כי יקרא רגע בין הערבים ערב, כי כן כתוב: בין הערבים תאכלו בשר (שמות טז, יב), ושם כתוב: בתת ה' לכם בערב בשר לאכול (שם, ח). ובהדלקת הנרות כתוב: יערוך אותו אהרן ובניו מערב עד בקר (שמות כז, כא). וכתיב: עולות לה' לבקר ולערב (עזרא ג, ג), וכתיב: ואת הכבש השני תעשה בין הערבים (שמות כט, לט). והנה על הפסח, שכתוב בו בין הערבים, מצאנו: שם תזבח את הפסח בערב, כבא השמש מועד צאתך ממצרים (דבר' טז, ו). פי', כבא השמש לצד מערב. ואין זה משמע ביאה, כי הוא היפך יציאת השמש, מדכתיב: השמש יצא על הארץ (ברא' יט, כג), שהחל להראות על הארץ. וככה: ובא השמש וטהר (ויקרא כב, ז), שלא יראה על הארץ. והנה כתוב על מקרה לילה, והיה לפנות ערב ירחץ במים (דבר' כג, יב). ואם אין הדבר כן, יבאר לנו מה הפרש יש בין כבוא השמש של פסח ובין כבוא השמש של מקרה לילה. וככה ובא השמש וטהר (ויקרא כב, ז). אמרו המינים, כי שלשה ערבים הם, וראייתם בעבור שמצאו עד הערב השלישית (ש"א כ, ה). והם לא הכירו האמת ולא הבינו, כי כתוב: מחר חדש וגו' ושלשת תרד מאוד (שם שם, יח - יט), שפירושו כאשר יהיה היום השלישי מהיום הסמוך לערב השדה שאתה נסתר שם. ובעבור זה אמר עד הערב השלישי. ועתה אשוב לפרש. דע, כי משקל ערבים לעולם נופל על משקל שנים, כמו אבנים (שמות א, טז), וכמוהו לוחתים (יחז' כז, ה), וככה דרכים (משלי כח, ו). והעד יפול באחת (שם). וככה שמים, כי הם שני סדני הגלגל, שהם כמו מסמרות נטועים שעליהם משענות הגלגל, וככה לנטוע שמים (ישעי' נא, טז), וכבר פירשתי בס' השם הנכבד, כי שמים מגזרת שם ישר נכח עמו (איוב כג, ז), רמז לשני מקומות. והנה יש לנו שני ערבים, האחד עריבת השמש, והוא עת ביאתו תחת הארץ, והשני ביאת אורו הנראה בעבים. והנה יש ביניהם קרוב משעה ושליש שעה. אז יבא בעל קרי אל המחנה, וידליק אהרן את הנרות. אמר הגאון רב סעדיה ז"ל, מדת מזבח העולה חמש אמות אורך, וחמש אמות רוחב. ובמדה הזאת לא יעמדו כי אם כהנים מעטים, שהם זורקים דמי הפסחים קודם שיקרשו. והנה בימי יאשיהו (דהי"ב לה, א), שהיו ישראל מועטים לא יכלו הכהנים לזרוק דמי הפסחים והשלמים ששחטו לזרקם לשעה ושליש שעה, ואף כי בהיות כל השבטים בארצם. והנה היתה קבלה, שיחלו לשחוט מהרגע שיתברר לאדם כי השמש נטה לצד מערב. והזכיר הכתוב בין הערבים, שרוב הפסחים היו אז נשחטים שם, והוא סוף הזמן שלא יעבור עד עריבת אור השמש:

    The whole discussion is how much of the afternoon is "erev".

    Again -- a qorban can't be shechted after sheqia. This quote has totally irrelevant. R' Saadia Gaon is talking about a mitzvah performed between minchah gedolah and sheqia, saying that most of the slaughtering occured in the last 53% of the window. Probably said 1-1/3 hours just as a way of saying a little more than half (1.5 hr).

    FWIW, I'm struggling with a different problem in RSG. Pesachim 5:7 says the qorban was brought in three shifts, but the third shift was so small they didn't have time to finish the enrie Hallel. So, how could most of the offerings have been in the last 80 min?

    But there is nothing here overthrowing the common belief that the geonim held one way, a number of major rishonim held another (which therefore caught on in practice), and under the Gra's influence we reverted to the earlier pesaq.

  28. והנה יש לנו שני ערבים, האחד עריבת השמש, והוא עת ביאתו תחת הארץ, והשני ביאת אורו הנראה בעבים. והנה יש ביניהם קרוב משעה ושליש שעה. I.e. the sun goes under the earth. then we keep on sacrificing for 80 minutes. This is what it says in the gemara in zevachim that you have to stop the sacrifice at the beginning of bein hashemashot. the tosphot over there deals with the question of why ne would have to stop the sechita even though it is not night. But still this is what saadia is saying here. step one shkiya (in his words the sun has come under the earth). step two 80 minutes. then step three we stop the shechita of the pesach.
    I don't deny that rav hai geon held differently. But the idea of "the sun going under the earth" in my opinion can't refer to mincha ketana. (also the math thing i am not making up here. The regular rabbainu tam that you have got 4 mils from shika to night. the last part of this period is bein hashemashot.
    if a mil is 18 minutes then bein hashemashot starts after 59.5 minutes . That is is the night begins after 72 minutes the one stops melacha 12.5 minutes before that. if a mil is 24 minutes then the night begins at 90 minutes and bein hashemashot is 3/4 of mil before that which comes close to 80 minutes

    as for you other points. i don't know what historians say say about this type of thing but professors vary in their quality.

  29. i am sorry if i did not make it clear. i started my last note with a quotation from the piece in the Ibn Ezra. he says says that after the sun goes down we keep on doing the sacrifice of the pesach for 80 minutes. the rest of my note was to show how this would work to rabbainu tam

  30. Except we don't keep on sacrificing after sheqiah. Given the IE you focused my attention on, I would be forced to conclude he is saying that qorbanos are offered until what R' Tam calls the 2nd sheqiah. Since it's non-negotiable (it's in just too many gemaros) that qorbanos must be slaughtered and their blood sprinkled before sheqiah. And that is 80 min after the first -- following which we still have to yet wait for tzeis!

    And that would explain my earlier point about why he doesn't use the words "ad tzeis" if he meant a well known time. And because he is trying to distinguish between two definitions of sheqiah, the word "sheqiah" wouldn't be helpful either.

    Also relevant is IE on Bereishis 1:18:

    ולמשול: יום התורה משעת צאת השמש עד בואה, והלילה מעת ראות הכוכבים. וצדקו האומרים עפ"י שלשה עדים. ודע כי עת שתחשך השמש יהיה ערב עד שעה ושליש שעה שיראה כמו אור בעבים, וכן הבקר אור קודם זריחת השמש. ובצאת אור השמש ביום, ואור הלבנה בלילה, יבדילו בין האור ובין החשך:

    But in any case, this understanding isn't compelled by RSG's actual words. It is the IE's take on RSG's position. And we know the rishonim did things differently than the geonim. It's not just R' Hai Gaon who gives the earlier tzeis. R' Sherira also endorses the position later associated with the Gra, and describes it as common practice. It's what "everyone did" back then. Just like now. (Even those who hold by R' Tam only do so lechumerah, not like they feel it's iqar hadin.) IOW, it's more likely to be in how the IE read RSG than RSG giving a peshat that no one held lemaaseh.

    But regardless of what R' Saadia Gaon held, I stand by my general statement that "the geonim" held like the Gra eventually would, if R' Sherira Gaon refers to it as accepted.

    BTW, I speculated that the IE might be using degrees, more as a fun way to match him to R' Tam than anything serious. R' Tam's 72 min at equinox could be 80 min slightly later, on 15 Nissan. Turns out R' Chaim Druck (Oros Chaim pg 333) argues that the IE does use angle, not absolute time!

    BTW, his results are different than your experiment, and explains the astronomy of R' Tam by saying that RT holds that tzeis is 3 stars near the western horizon, which goes dark last. And even then he says RT had an 18 min (absolute, not angle) mil.

  31. my impression this by the time of rav hai geon that the yeshivot had moved to what is called present day Libya and that rav hai and his son were not the center of Judaism in any sense. I don't think that what they would write would be representative of what everyone is doing. The story as far i I remember it is that the Muslim rulers had started raising tax and Jews simply decided to move away from bavel.

  32. Adam, I found "twilight" on wikipedia. http://en.wikipedia.org/wiki/Twilight

    Secular culture has 3 twilights:

    Civil twilight: when the sun is at until 6deg below the horizon. (Or the reverse, at sunrise.) This is when the brightest stars and Venus -- ayelet hashachar -- are visible.

    Nautical twilight: 6-12 deg below the horizon. Before which, you can't see enough well-known stars to navigate.

    Astronomical twilight: 12-18 deg below. After which, it's dark enough for good astronomy. (Well, not when you're as close to NYC as I live...)

    12 deg below the horizon is 4/5 of a sha'ah zemanis. I still can't say how you erred in your experiment, but it doesn't fit the data. The geonim's definition of tzeis is within the range of the data, depending on defining which stars you need 3 of. But the rishonim's definition does not. 72 min on the equinox is 18deg, when you have 3 of the dimmest stars visible to the typical eye -- astronomical twilight.

  33. The question is not what is "twilight" but the word that the gemara uses "medium," i.e. the medium of all stars that are visible to the naked eye.

    Astronomical night is when Sun is lower than 18 degrees below the horizon. That means all stars are visible that can be seen by the naked eye.
    and this still fits close to Rabbanu Tam and fits exactly with what I saw that at 45 to 50 minutes is the time when medium stars come out.
    (but again rabbanu tam depends mainly on the contradiction of gemarot between shabat and pesachim )

    This would at least explain reb moshe feinstein and the chazon ish that said to wait until about 50 minutes as far as I remember. At least this was the point of Rav Montag (a rosh yeshiva in Netiovot the foremost disciple of Issacahar Meir of yeshiva HaNegev and a close friend of Baba Sali fame.)--besides that, that guy does in fact know how to learn - at least to be able to defend positions of Reb Elchanan and company. (I did not hear chidushim of his own from him but he could defend positions that I attacked.)

  34. 3 medium stars can't mean every last star. The smallest star can't be a "medium" one. Thus, tzeis must be measurably before astronomical twilight. So the scientific data behind astronomical twighlight rules out both 72 and 90 minutes.

    Looking in the reverse, R' Moshe's 50 min comes to 12.5 deg. The frequently used 8.75 deg for Shabbos (3 small stars) also fits the expectations of the secular world -- for suitable definitions of "small".

    But every last star is not the definition of tzeis, even lechumerah. Wikipedia agrees with the Gra that R' Tam's shitah doesn't fit reality.

  35. I agree that medium can't mean the smallest star that come out at 90 minutes. If all stars are viable after 90 minutes then it stands to reason that the medium ones are around 45 minutes. And this is in fact what is seen. However you are right this a long way from Rabbanu tam. But it also along way from the Gra and Rav Hai Geon that would have three medium ones at 18 minutes for a 24 minute mil (or 13.5 minutes). This is also far away from 45 minutes.

    And when we look at the Gemara we don't see that the Gra deals with the issue that Rabbanu Tam deals with. he simply goes and explains how the different Gemaras about "mishtiska hachama" could be in accord with his explanation. But he does not give convincing evidence. And he still leaves the Gemara about 4 mils as a blank-"peshat"less. I once thought the regular part of the Gemara in shabat (before you get to the stars part) was like the Gra until I rechecked it and saw that it refers to the Western horizon --not the East and this convincing evidence for Rabbanu Tam.
    I admit the Gra must have had some explanation for all this. I freely admit this. Perhaps his explanation is buried somewhere in that note of his on the shulchan aruch. It is common to discover the gra has a entirely different explanation of a sugi that anyone could have dreamed on. So perhaps that applies here also. his I admit. and in fact i would even go so far as to say that anyone who depends on the gra in all of his decisions has the right to do so here also. (I hope i don't have t eat my words here--but in general i am think the gra is on the level of a rishon and thus qualified to disagree with the other rishonim.)

  36. Even "three tiny stars" has to be earlier than the end of astronomical twilight, since that's every tiny star. But they could be close.

    I don't think you need to invoke the notion that the Gra is a throwback to the rishonim for this, since he is supporting the position of geonim. "All" he is doing is reviving an opinion after common practice rejected it -- which is huge in itself. But it's not the Gra vs R' Tam et al on his own.

    More after I double-check the math for deg per minute on the soltices and equinoxes in EY. I was working with the simple assumption that on average, the sun travels 360deg in 24 hours. But the truth is that if we're talking about depth under the horizon, and neither EY not the middle of the EY-Bavel yishuv aren't at the equator, we only want one component of that motion.

    So, I'm taking some of the code behind a Hebrew calender I wrote with zemanim and daily learning schedules, and checking how it's done.

  37. So, I had a chance to check the numbers.

    In Y-m, civil twilight is 24-28 min, nautical twilight is 52-62min, and astronomical twilight is 81-100min. Meaning, 72 min in EY is not quite zero stars, but real close. Not when you see 3 small stars, unless by this you mean diffuse things like nebula or galaxies, rather than points of light.

    Whereas the Gra holds 3/4 of a mil, 13-1/2 - 16-7/8 min. Well shy of civil twilight, when one can only see Venus and three bright stars.

    It really looks like RMTukachinsky and RYLevi's experimental data, 22 min for most people 15 min for experts (respectively), fits the range for when astronomers would assume 3 medium stars could be seen.

    It also looks like the Orchos Chaim's take on R' Tam, that he was saying when 3 stars on the western (most lit) horizon could be seen, would also fit the data. (Also the Minchas Cohen's -- that R' Tam was saying that by 72 minutes you can be sure it is after the actual tzeis even in Troyes.)

    But pashut peshat in R' Tam still does not fit the data.

  38. RAZ, I decided to stop hijacking a post about experimental yeshivos as well as bring this discussion to a broader group of people. See my post at
    http://www.aishdas.org/avodah/getindex.cgi?section=Z#ZMANIM%20FOR%20TAANIYOS . The current incarnation of this thread starts at my post in digest v29n32.

  39. Now that I took the tangent elsewhere, I want to return to the intended topic of this discussion chain -- yeshivos that promote experimentation.

    There are two elements to experimentation:

    1- It promotes both
    a- critical and
    b- independent thinking.

    2- Experiments are experiential, not education through description of the ideas in words -- whether from the teacher, books or on-line. Experience makes a
    a- more lasting and
    b- deeper impression.

    I want to focus on #2 a little more. The problem of akrasia (why people can choose things they know are wrong) is mostly about the gap between things we know in our heads, and our gut -- where our first instincts, our desires, and our emotional proclivities reside.

    If we want to make not only more informed students but also students that internalized those truths and whose characters and decisions are shaped by that Torah, we need more ways to promote experiences in yeshiva.

  40. Thanks, Micha; I tend to agree. And with akrasia, I just learned a new word!

  41. Micha you wrote: "and astronomical twilight is 81-100min."
    That means in that that is when you see all starts that are viable to the naked eye. Therefore a half of that is when you see the medium stars.
    but to answer your thought about 22 minutes again you really have to be in Israel to see this. Wait for 22 minutes on some mountain far from city lights. You will see start that are very large and some that then look medium. But then wait for an hour and you will see something remarkable--the stars you thought were medium were actually gigantic compared to most stars and could not be called medium at all. This is why the gemara implies you have to see the medium of all stars. that is the only rational explanation of what the word medium means.