when’s the last time for kiddush levanah?

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  • #1549194

    jew boy2
    Participant

    when’s the last time for kiddush levanah?

    #1549384

    iacisrmma
    Participant

    (29 days, 12 hours, 793 chalakim)/2 from the previous Molad. In other words 14 days, 18 hours and 396.5 chalakim from the previous Molad. The Molad for Tamuz was Wednesday evening 5 minutes and 7 chalakim after 6. 14 days later was the entire night of Tes Vav Tamuz. If you haven’t said it yet, you missed the zman.

    #1549408

    ChadGadya
    Participant

    iacisrmma,
    Don’t forget to correct for the time difference to Jerusalem local solar time.
    This equals the time difference to Israel minus the difference between the local solar time there and the mean Israeli time which is quite a bit off the center of the time zone. The difference to subtract is exactly 20 minutes and 56.5 seconds at the longitude of the temple mount.

    #1549411

    ChadGadya
    Participant

    Follow up: Also don’t forget to add an hour during the summer when the clocks are an hour ahead.

    #1549442

    iacisrmma
    Participant

    The english Ezra Torah Luach for Tamuz states “The final time for the sanctification of the New Moon for Tamuz is the entire night following Wednesday, June 27, (15 Tamuz). (Pages 145-146).

    #1549426

    laskern
    Participant

    As a side information there is a gematria implying the 29 1/2 days and 793 chalokim from one molad to the next. The verse החדש הזה לכם ראש חדשים ראשון הוא לכם לחדשי השנה adds up exactly כמה תשעה ועשרים ומחצה יום ותשצג חלקים totaling 2658.

    #1549464

    laskern
    Participant

    To find any molad we must find the first molad.

    To find the first molad Rambam Hilchos Kidush Hachodesh (6,8) Take the day Adam Horishan was created and subtract a year.
    He was created on Friday at 8 AM = 6 day 2 hr = 6 day 14 hr counted from Thursday 6 PM when the 6th day begins.
    When taking a 12 month year molad difference when divided by 7 which is for one month 1 day 12 hrs 793 chalkim multiplied by 12 we get
    4 days, 8 hrs 876 chalokim.
    Going back a year from his creation by subtracting this from 6 day 14 hrs we get 2 days 5 hrs and 204 chalokim with the mnemonic בהר’ד is the first molad.

    • This reply was modified 7 months, 4 weeks ago by  laskern.
    • This reply was modified 7 months, 4 weeks ago by  laskern.
    #1549551

    kollelman
    Participant

    Is there an online calendar that shows the latest times?

    #1549538

    ubiquitin
    Participant

    A few points
    “(29 days, 12 hours, 793 chalakim)/2 from the previous Molad.”
    This isnt according to all. The Mechaber says 16 days. The MAgen Avraham understands this to mean you have until the end of the 16th day. The MB understands this to mean meis leis ie 16 x 24 hours from the molad.
    Iacrisma is right according to Ashkenazim, as the Remah says it is half of 29 12 793.

    “Follow up: Also don’t forget to add an hour during the summer when the clocks are an hour ahead.”

    A more important follow up is correcting for where you live.

    The molad isnt based on the time that you see on a clock. It is an average molad taken by adding 29 days 12 hrs and 793 chelakim to the previous molad.
    The time that is announced in shul is the time that this molad occurs in Yerushalyim real time. today we use standard time. Ie a chunk of the globe ~1/24 the circumfrence all has the same time. In Yerushalyim the molad occured as Iacrisma said “The Molad for Tamuz was Wednesday evening 5 minutes and 7 chalakim after 6. ”
    If you were in Yerusahlyim and checked the time on your clock that the molad occured. Your clock read 5:44 and 7 chelakim (Israel standard time is 21 minutes earlier than natural time) due to DST this is 6:44 and 7 chelakim.
    In N.Y. which is 7 hours “behind” Yerushalyim, the molad occured when the clock read 11:44 and 7 chalkim on Wednesday morning. Thus there is even less time than iacrisma indicated if you are west of Israel .

    (Rabbi Heber argues that leap seconds should be subtraccted as well, though that obviously has little, if any, practical significance)

    #1549582

    ChadGadya
    Participant

    ubiquitin,
    Did you even read my first post (directly before the one that begins “Follow up…”)?
    I said everything you said, just in fewer words and with more accurate numbers.

    Although the slowing of the earth’s rotation is important, leap seconds per se are not relevant as they are added to keep solar time in sync with an arbitrary measure which came about due to lots of international confusion circa 1958 (google ephemeris time, terrestrial dynamic time, and international atomic time if you want to partake in some of that confusion!)

    What is important is the value of something called ΔT (delta T). This is a measure of the ongoing difference between a time scale based on the rotation of the earth and a time scale based on seconds of a fixed length. The discrepancy between today and the time of the gemara is about 3 hours (with an uncertainty of a good few minutes either way). This is a very significant amount of time, but we don’t take it into account when fixing our calendar (the date of rosh hashana depends on the molad of tishrei with certain postponement rules), and presumably we shouldn’t take it into account for kidush levana either. Lo nitnah torah lemalachei hashareis.

    #1549640

    ubiquitin
    Participant

    I ĺ”said everything you said, just in fewer words and with more accurate numbers.”

    I read it quickly and missed that line. Sorry

    “leap seconds per se are not relevant as they are added to keep solar time in sync with an arbitrary measure which came about due to lots of international confusion circa 1958 ”

    Wonderful speech on leap seconds. Though they may still be relevant. 27 leap seconds have been added to date . Of course these don’t change the halachic time. Thus when your clock says say 11:44:35 (as mine does now) as far as halacha concerned it is 11:44:08.

    Similarly as I assume you know. The Gregorian changes do not affect how we calculate tekufos for vesein tal umatar. Thus when the molad occurs at 6:05:23 the time in your clock will be 27secinds earlier in addition to correcting for dst, your local time and of course the 20 min 56.5 seconds for solar time (not to be confused with the far less accurate 21 minutes that I dared write)

    #1549654

    adocs
    Participant

    CG,

    “The discrepancy between today and the time of the gemara is about 3 hours (with an uncertainty of a good few minutes either way). “

    Please explain.

    #1549687

    ChadGadya
    Participant

    ubiquitin,
    Please read my posts more thoroughly before responding. Leap seconds have been introduced to keep in sync with an arbitrary time scale which has nothing to do with halacha. Before the first leap second was introduced that scale was already way off from what is relevant to halacha. What is relevant to halacha is a scale based on seconds of fixed length where each of those seconds from the time of chazal through today stayed equal to the mean solar second at the time of chazal. This would be about three hours off by now. Please google universal time, terrestrial time, and delta t for more information.

    adocs,
    The rate of the earth’s spin is slowly changing, so if we add 86400 seconds for every day that has passed from the time of the gemara, but keep those seconds fixed equal 1/86400 of the length of the mean solar day AT THE TIME OF THE GEMARA, we end up with a time which is about three hours off from what is currently shown on our clocks. Chazal gave us a fixed amount of time between molads. They could only have meant in their time scale, which means our calculations are off by this amount. However halachically we don’t take this into account when fixing our calendar.

    #1549716

    ubiquitin
    Participant

    “Please read my posts more thoroughly before responding.”

    Right back at you.
    I’ll explain as simply as I can .
    Suppose halacha was you have until exactly six hours to reply to this post otherwise this conversation ends.
    I am typing this at 8:46 (my local time) that means you have until 2:46 pm. (If you live in Israel you have to adjust for that. So in 6 hours your clock would read 9;46 pm) If your clock is five minutes ahead. You would have until 2:51on your clock (for simplicity sake let’s keep you in my time zone). In other words the halacha wouldn’t change based on what your clock said it is 6 hours after my posting time period. You dont lose 5 minutes because your clock is different than mine
    Are you with me so far?

    Even if you intentionally set your clock 5 minutes ahead as some do to keep them on time. You still would have 6 hours after 8:46 which on your clock would be 2:51

    Even if you did some calculation and determined that all of our clicks are wrong and the real time is 5 minutes later. Halacha still wouldn’t change and you’d have 6 hours after 8:46 (on my mistaken) clock which would be 2:51 on your note accurate clock.
    Still with me?

    Now lets say instead of you setting your clock ahead it was a regulatory body. And instead of 5 minutes it was 27 seconds.
    My time doesn’t change (since the time of the molar isn’t affected by their change) I posted at 8:46:00. But your more accurate clock reads 8:46:27. Six hours after the molad isn’t 2:46:00 (of course it is in halaxhic time but that’s not what your clock days) your clock will read 2:46:27 exactly 6 hours after my post went up at 8:46:00 (halachic time)

    #1549731

    ChadGadya
    Participant

    ubiquitin,
    For goodness’ sake, when will you be quitin?
    Here we go for the third time:
    Obviously we are now 27 seconds more out of sync with chazal’s molad calculation than we were in 1972 before the leap second business. But WHAT IS THE SIGNIFICANCE OF THAT in comparison with the approximately 3 hours that the pre-1972 time scale was ALREADY out of sync!? (And which we don’t take into account for determining our calendar!)

    #1549784

    ubiquitin
    Participant

    “For goodness’ sake, when will you be quitin?”

    when you get it.
    I am a patient teacher (though admittedly perhaps not the most effective one)
    this is part 1 of 2

    “Obviously we are now 27 seconds more out of sync with chazal’s molad calculation”

    While that is obvious. that isnt at all what I am saying.

    Read my last post where I spell it out with an example. The point is that any adjustment made to your clock. (whether due to time zones, DST, standard time or leap seconds or even if you just set it at a different time fr whatever reason) Will NOT affect the time of the molad. I did not say we would “take into account for determining our calendar” We dont. However it DOES affect the time that your clock reads as it relates to the molad, since the time of the Molad remains fixed (2/5/204 + (29/12/793) + (29/12/793) etc etc) when changes are made to YOUR clock will be relevant.

    #1549796

    ubiquitin
    Participant

    PArt 2 of 2

    I thought my 6 hour posting example was good, clearly not.

    I’ll try another approach:

    Lets rewind suppose you lived in Yerushalyim in the 1800’s before the advent of standard time. Determining the time to stop kiddush levana was easy. You listened to the molad and added 14 days, 18 hours and 396.5 chalakim. The Molad announced was based on the same clock you had hanging on your wall. So if the molad was announced at Wed eve 6:05 7 chelakim. you added the above and you have until Thurs afternoon 12:27:25 . And until your watch says 12:27:25 on Thursday afternoon 2weeks after the molad you can say kiddush levana (assuming you see it of course).
    Now you are somewhat knowledgeable and you know that this time is off from the actual lunar conjunction, but you also know that that is completely irrelevant.
    So far so good.

    Things get complicated with the advent of Standard time, when 21 minutes (or as you more accurately put it 20 minutes and 56.5 seconds) are added. Now your watch no longer displays the same time that is used to announce the molad. The time announced for the molad DOESNT CHANGE it is still Wed eve 6:05 7 chelakim. Only now you can no longer just look at your watch and say kiddush levana until Thursday afternoon 12:27:25. As your watch is using a different time than the molad. you have to convert your time by subtracting 20 minutes 56.5 seconds and you can only say Kiddush levana until Thursday afternnon 12:06:28 (I’m rounding the half second)
    Again this isnt because the change in time has any bearing on the molad. It doesnt. But it does have bearing on the time your watch displays and as it relates to the molad.

    Fast forward to the 1970’s onward. More changes are made to the time displayed on your watch. Again not to the molad, the time of the molad satys the same. But the time on your watch is different.

    I’ll copy and paste my last paragraph regardign standard time, whih I think you may have understood. Just making relevent changes for leap seconds, which is the EXACT SAME principal
    For simplicity in this scenario there is no standard time

    Since the 70’s 27 leap seconds have been added. Further changing the time your watch displays as it relates to time that is used to announce the molad. The time announced for the molad DOESNT CHANGE it is still Wed eve 6:05 7 chelakim. Only now you can no longer just look at your watch and say kiddush levana until Thursday afternoon 12:27:25. As your watch is using a different time than the molad. you have to convert your time by subtracting 27 seconds and you can only say Kiddush levana until Thursday afternnon 12:26:58

    Of course in reality both come into play and you need to subtract both the change to standard time and leap seconds
    giving you until 12:06:01Thursday afternoon.

    Of course as I mentioned the practical significance of this is little if any

    #1549844

    adocs
    Participant

    CG,

    Are you saying that the length of the day during the time of the Gemara vs. the current length of day is a difference of 3 hours ?!

    #1549846

    iacisrmma
    Participant

    kollelman: The Ezras Torah Luach is available online at ezrastorah dot org. You have to look at each month individually.

    #1549860

    ChadGadya
    Participant

    ubiquitin,

    Your latest dissertation has added nothing to my already perfectly complete understanding of everything you have been saying. Unfortunately you still haven’t understood what I am trying to say. And in additiion, you have the concept of leap seconds EXACTLY BACKWARDS. I am apparently a worse teacher than you. I will try to improve. On your side please try to read slowly and carefully.

    Chazal said that molad to molad is a certain time interval, equal to 29 and a half and 793/(1080*24) days or 2551443.3 seconds. The second then was defined as 1/86400 of a day. The days in their time were a certain length. But the length of the day has been changing due to the slowing of the rotation of the earth, while the molad to molad time has presumably remained constant – 2551443.3 of chazal’s seconds. Our clocks and watches have had their second hand tickings constantly adjusted throughout the centuries to stay 1/86400 of the current day. This is equivalent to sneakily adding thousands of leap seconds smeared out through the years, and has accumulated to about 3 hours.

    What happened from the mid 20th century onwards (sort of, more or less, cutting through the confusion of various ideas and scales that were put forward), is that the second was redefined as a fixed amount of time based on a certain frequency of radiation from cesium atoms. Since the earth’s rotation continues to change, a fixed length of second comes with the disadvantage that mean midday will start to slowly move through the clockface to all kinds of ungodly hours. Thus leap seconds were introduced to keep clocks that are ticking with the new fixed second in sync with the sun.

    Thus leap seconds do not, as you seem to think, adjust the natural mean solar time to conform with some arbitrary scale that the scientists came up with, on the contrary, it adjusts the arbitrary fixed second to conform with mean solar time.

    So we come to the crux of the argument, which I’ll put in the form of a “mimah nafshach”:

    If the factors affecting the rotation of the earth do not affect the molad to molad time, which remains a fixed 2551443.3 seconds of fixed length, then these seconds can only be those of the time of chazal, in which case 27 seconds are the least of our worries, as we have about three hours to consider.

    If on the other hand we are not to take account of this discrepancy, either because lo nitnah torah lemalachei hashareis (it is impossible to know the discrepancy exactly without a large margin of error), or because some mysterious cosmic forces have been slowly changing the molad to molad time to keep it equal to chazal’s measure in contemporary days and seconds, THEN LEAP SECONDS ARE NOT TO BE TAKEN INTO ACCOUNT EITHER.
    This is because leap seconds do the exact opposite of what you think. If chazal meant us to stay with mean solar time even though it is slowly changing, then the reforms in the definition of the second of the mid 20th century would mean that without leap seconds our clocks would slowly drift away from the correct time scale of chazal. The leap seconds actually bring the new fixed time scale of our clocks back to mean solar time.

    So to recap, leap seconds are irrelevant, either we are three hours out, or we are right on time.

    #1549893

    laskern
    Participant

    The online calendar is myzmanim.

    #1549896

    ChadGadya
    Participant

    adocs,

    3 hours would be the accumulated gain over the centuries of a clock ticking fixed seconds equal to 1/86400 of chazal’s days, over our clocks. The actual difference in the length of the day between chazal’s time and ours is only about 35 – 40 milliseconds!

    If you are looking for a “practical” consequence lehalacha from this difference, consider the 18 minutes it takes unworked dough to become chametz. This is defined by chazal in maseches pesachim to be 1/40 of 12 hours or 1/80 of a full day. However, due to the changing length of the day, dough would become chametz on our clocks at about half a millisecond before the 18 minutes are up. You can see why I put the word practical in quotes!

    #1549899

    ubiquitin
    Participant

    “Your latest dissertation has added nothing to my already perfectly complete understanding of everything you have been saying”

    This is demonstrably false.

    You said “Thus leap seconds do not, as you seem to think, adjust the natural mean solar time to conform with some arbitrary scale that the scientists came up with”

    I in no way implied or said that and in fact said the opposite. The molad and the time used to calculate it has not changed. Our clocks have. OR as you put it exactly right
    ” it adjusts the arbitrary fixed second to conform with mean solar time.”

    In other words your clock now reads a different time than that used to calculate the molad.
    There are already many differences between your clock and the clock used for the molad, this is but one more.

    Now to go through your mimah nifshach
    “If the factors affecting the rotation of the earth do not affect the molad to molad time, which remains a fixed 2551443.3 seconds of fixed length…”
    Again the molad time remains constant it doesnt change. The time of the molad does not depend on time zones, standard time or leap seconds

    I dont understand your other tzad.
    Again the time of the molad doesnt change. But the time on our clock does.

    Perhaps this will help you out.
    Let me know where I lose you.
    step 1. The molad occured Wed eve 6:05 7 chelakim.

    step 2. you have 14 days 18 hours and 396.5 chalakim later to say kidush hachodesh which means that (before the advent of standard time) you can say it until Thursday afternoon 12:27:25

    step 3a. The above time doesnt change just becasue your clock changes. In other words you cant just wake up Thursday night when your clock says say 6 PM turn the hour hand back 6 hours and say great I still have 27 minutes to ay kiddush levana. In other words the time on your clock doesnt matter it is the relative time since the molad.

    still with me?

    step 3b if you set your watch 5 minutes later so that when your watch reads 12:27:25 it really is 12:22:25. Then when your watch reads 12:27:25 you still have 5 minutes

    step 3c if the government changes the time to 5 minutes later (or 20 minutes 56.5 seconds earlier). Once again that has no bearing on the “real time” you have for kiddush levana which is stilll 12:27:25 Thursday afternnon based on natural local time. Only that your watch wont say that it will say 12:06:28

    I’m failry certain you are with me to a certain extent so far.

    Finally
    step 4 If regulatory bodies change the time to 27 seconds later (regardless of their motive , or how accurate they are). The n again, exactly as in 3a, b, c. The time that the molad occurs doesnt change the mean solar time at which yo uhave to stop kiddush levana doesnt change. But at that same natural local time of 12:27:25 your clock will read 12:27:57 (I’m sorry if I had that backwards earlier)
    Thus just like you have to subtract time zones, change to standard time, extra minutes you added to your clock display for any reason whatsoever. You would also subtract extra seconds added to your clock by you or anyone else.

    I double checked Rabbi Heber’s sefer shaarei zemanim and on page 22 footnote 3 he says what I have been trying to explain to you. (though not in detail )

    You end by saying “So to recap, leap seconds are irrelevant, either we are three hours out..”
    I’m worrying that we are talking about different things (although yo u claim to have “perfectly complete understanding of everything you have been saying.”) I am not at all discussing the accuracy of the molad. Not in the slightest.

    #1549913

    ubiquitin
    Participant

    Another attempt

    Many wait 6 hours after fleishig to eat milk.
    So if you finished eating 12:00 PM you don’t eat milk until 6:00 PM

    Say you ate meat on 12/31/16 at 11:00 PM You make a mental note that you can eat milk 6 hours later on 1/1/17 at 5:00 AM.
    Well wouldn’t you know it an extra second was added at 23:59:60

    This means if you want to be exact about it you will be milchigs on 1/1/17 at 4:59:59 which was 6 hours after 12/31/16 11:00:00.

    Again it isnt that anything changed with your minhag of waiting, or your start time. Rather it is that the 6 hours that get added have nothing to do with regulatory agencies.

    Now imagine there was some halaca that every 6 hours after meat you had to , say pat your head until you eat meat again. So you eat meat at 11:00 PM and now become vegan, you then pat your head at 5:00 AM, 11:00 AM, 5:00 PM, 11:00 PM etc etc.

    when you encounter a leap second, that has no bearing on your halachic obligation to pat your head every 6 hours. Only now the time displayed on your clock is different. so you pat your head at 11:00 PM 12/31/16 followed by 4:59:59 AM on 1/1/17 followed by 10:59:59 etc etc. the 6 hours interval doesnt change, the starting point doesnt change, but we disregard an external change made to the clock display (again although it may be accurate) When another leap second gets added. the head tapping will once again shift to 4:59:58.

    Again the starting point and interval between taps isnt changing.

    Say 27 leap seconds have been added. and you want to tap your head at the exact second required.
    You can no longer say well we last ate meat 11:00 PM 12/31/16 so I just keep adding 6 hours and today I tap my head at 5:00 PM. While that is TECHNICALLY true. If you added 27 leap seconds to your clock. when it is next time for you to tap your head it will read 4:59:33. This is an exact multiple of 6 hours after you last ate meat.

    The molad is the exact same thing. It isnt based on any actual natural event (though many assume it is, sure the idea is sort of based on an average but as you may know this changes and is no longer accurate at all, and was never accurate on any given month)). It is simply taking a starting point (BaHaRaD) and adding a regular interval 29-12-793 (or 1-12-793) you will get your molad. However much like our head tappping friend., who is doing the exact same thing, To be precise as that molad relates to the time on your clock, you will need to subtract any leap seconds that have been added).

    I hope this example helps, if it makes it worse dont get caught up in it

    #1549950

    ChadGadya
    Participant

    ubiquitin,

    I think this will have to be the last time I respond, as we seem to be getting nowhere.

    Steps 3 to 4 are wrong.
    If the seconds are the correct length, then of course you are right that if the government decides to add 27 leap seconds, the true time of sof zman kiddush levana will read on my clock 27 seconds less than it would have.
    But the seconds have changed since the new definition, and leap seconds bring them back to where they should be. This is what I mean that you have it backward.

    As a concrete example, let’s say that half the molad period is exactly 1275722 seconds. If I redefine my seconds as each being 27/1275722 of a second shorter than they should be (shorter than chazal had in mind), then after 1275722 seconds as read on my clock, we will still be 27 seconds short of the zman, and on the contrary we need the extra 27 leap seconds to bring my clock reading back into line.

    This is exactly what has happened with the redefinition of the second, except that instead of being redefined as shorter by a factor of 27 in 1275722, it is only shorter by 27 in about 45 years worth of seconds.

    We add a leap second every time the discrepancy between atomic time and mean solar time adds up to a whole second. To reiterate, this discrepancy is caused by the fact that we have redefined the second to be somewhat less than 1/86400 of the current mean solar day (the second that chazal had in mind), and the leap second FIXES this discrepancy.

    This was my second tzad. The first tzad was that chazal didn’t mean 29.5 + 793/(1080*24) of each generation’s contemporary solar day, but of their solar day always, in which case we are about three hours out.

    I don’t know Rabbi Heber and I haven’t seen his sefer, but if he says what you say he says, then he is making the same mistake as you.

    For your information, this is a subject that I have been interested in for many years, and what I am telling you here is not “google ben yomo”, but things that I have known for a long time.

    #1549971

    ubiquitin
    Participant

    “For your information, this is a subject that I have been interested in for many years, and what I am telling you here is not “google ben yomo”, but things that I have known for a long time.”

    I dont get the google ben yomo reference.
    I too have been interested in this for many years. Although unlike you I have done more through research. (you freely admit you arent familiar with a work on this very topic) I dont know you I am familar with him and his work.

    If you are interested in time related cocepts in general as they relate to halacha. I I highly reccomend his sefer it is called Shaarei zemanim. You may learn something

    Your discussion “As a concrete example, let’s say that half the molad period is exactly 1275722 seconds…” is anachronistic. (though admittedly the idea of subtracting 27 seconds is anachronistic too, though you earlier didnt like my rounding 20 minutes 56.5 sec to 21 minutes which is of course less of a difference than 27 seconds) Chazal’s times were not that precise. Nonetheless Any “correction” made is ignored.

    For example. While Tekufas Rav Ada is more accurate than That of Shmuel. It is still less accurate than what we know today, we still go with it although we can see Yomim Tovim sliding forward through the seasons.
    See Irv Bromberg’s website where he suggests various fixes too the calendar to correct for drift.
    Nonetheless even you accept his fixes. They wouldn’t change the halacha.
    The Julian calendar that we use for Vesein Tal and Birchas hachama is visibly off. As you may know while a more accurate one is avaliable we dont correct our calcualtion. We stick to chazal’s (although it isnt as precise)

    Another attempt
    In the back of R’ Dovid Feinsteins’s book on the calendar there are instructions to construct an excell spreadsheet with molados for 247 years

    The molad for Cheshvan 5928 will occur Tue Oct 13 2167 6:16 PM 0 chelakim
    Suppose I want to set a google reminder for the latest time for kiddush levana.
    So you add 14 days 18 hours 396.5 chalakim
    yielding Wed Oct 28 2167 12:38 PM (and 0.5 chelakim)

    I will be in E”Y so I subtract the 20 min 56.5 seconds that must be subtracted.

    Thus the latest time to say kiddush levana Cheshvan 5928 will be 12:17:03.

    Are you saying that isnt true. That there is no way to calculate when kiddush levana will end?
    Are you saying that no matter how many seconds, minutes? hours? get added to the calendar over the next 140 years I can jjust check my clock and as long as it says 12:17:02 I still have a second for kiddush levana?

    #1549994

    laskern
    Participant

    Does this go into the argument if efsher letzamtzem?

    #1550056

    ubiquitin
    Participant

    Btw CG

    Thanks for preservering. I finally get what you are saying your last post was better than your more cryptic earlier posts.

    Your conclusion isn’t correct. But I get what you are saying so thanks.

    #1550098

    ChadGadya
    Participant

    ubiquitin,

    Although I said I wouldn’t be posting anymore on this, the recent signs of progress in your understanding are encouraging, so I’ll give it one more shot. PLEASE, PLEASE, read slowly and carefully.

    Let’s go to your meaty/milky example. If I redefine my seconds as only five sixths of the length of a real second, AND HAVE MY CLOCK TICK THESE NEW SMALLER SECONDS, then surely you agree that I may not yet eat milky when 6 hours are up on my clock, as in reality only 5 hours have passed. The fact that I have changed my second does not affect the halacha.

    What I would need to do to in order to fix my problem (so that the true time I can eat milk will indeed be when six hours have passed as indicated on my new clock), would be to add a leap second every five seconds. Every time five seconds are up on my clock (which are only 5*5/6 = 4+1/6 real seconds), I would have to wait an extra leap second (of my kind of second, 5/6 of a real one) before ticking on again, in order that five real seconds should have passed while my clock still indicates “five seconds”.

    This is exactly what is happening with the real leap seconds. The second since antiquity, and certainly the second of chazal, is defined as 1/86400 of a day, whatever the length of the day may be. Then scientists discovered that the length of the day is slowly changing, so they redefined the second to be a certain fixed amount of time. This redefinition does not affect the halacha, which still uses the old definition even though it isn’t exactly constant as compared to nuclear radiation. Since the length of the day has continued to change, the new second as defined by the scientists is now LESS than 1/86400 of a day. THIS IS THE NEW SECOND THAT OUR CLOCKS NOW TICK. Our clockfaces still have 86400 seconds to 24 hours, so with the redefinition of the second comes the redefinition of a day too! If we didn’t add leap seconds, in about 20000 years average midday would be at 3 o’clock in the afternoon on our clocks! Obviously this would be uncomfortable for people, so they add leap seconds every so often to keep atomic time in line with solar time. The time AFTER the addition of the leap second is the true halachic mean solar time that chazal meant.

    When chazal said that molad to molad is 29.5 + 793/(1080*24) days, they meant halachic days, not the new days which are slightly shorter. The answer to the question at the end of your post is ABSOLUTELY YES. No matter how many leap seconds have been added over the 140 years, the time to say kiddush levana will be at 12:17:03 on my internet-connected clock. This is because the rules are that leap seconds are only added as necessary to keep atomic time in line with solar time. When we add a leap second, it means that the accumulated error of our clocks ticking the new atomic seconds, over a true solar clock, has reached a second, and we are CORRECTING for this. Please say you understand now!

    (I won’t go back into the other tzad, as you seem to be having enough trouble with this one.)

    #1550502

    Eli Y
    Participant

    CG: If you are looking for a “practical” consequence lehalacha from this difference, consider the 18 minutes it takes unworked dough to become chametz. This is defined by chazal in maseches pesachim to be 1/40 of 12 hours or 1/80 of a full day. However, due to the changing length of the day, dough would become chametz on our clocks at about half a millisecond before the 18 minutes are up. You can see why I put the word practical in quotes!

    Thanks for this amazing over-my-head discussion! I did a little research as you suggested in one of your posts and found that although the earths rotation is on average slowing down and extending a “24-hour day”, there are days that are faster than 24 hours including July 1 2018.

    Therefore, how could one know exactly how long on any given Pesach day what 1/40 of 12 hours or 1/80 of a full day would measure?

    #1550777

    ChadGadya
    Participant

    Eli Y’

    Obviously the time taken to become chametz does not depend on the time of year! Chazal meant 1/80 of the average day, which was then slightly shorter then than is now measured by 18 of our minutes.

    #1552040

    Participant
    Participant

    chadgadya, don’t worry. No one else understands ubiquitin either.
    Ubiquitin, don’t worry. No one else understands chad gadya either.

    #1552115

    ChadGadya
    Participant

    Participant, I actually suspect from ubiqitin’s “shetikah kehoda’ah” over the last couple days that he does finally understand me. When two people understand things differently it is difficult for each to put himself into the other’s paradigm and see things from their point of view in order to know exactly which points to elaborate on and how.

    #1552157

    ubiquitin
    Participant

    CG
    “I actually suspect from ubiqitin’s “shetikah kehoda’ah” over the last couple days that he does finally understand me.”

    No reason to suspect. I said so outright
    “Thanks for preserving. I finally get what you are saying your last post was better than your more cryptic earlier posts.
    Your conclusion isn’t correct (though I am less certain). But I get what you are saying so thanks.”

    I do mean the thanks sincerely.

    #1552161

    ChadGadya
    Participant

    Uh, ubiquitin, did you notice that a posted another whole reply since you wrote that?

    #1552175

    ubiquitin
    Participant

    “Uh, ubiquitin, did you notice that a posted another whole reply since you wrote th”

    Yes, though as I said “I finally get what you are saying ”
    I understand what you are saying .Repeating it wont make me understand better.

    #1552633

    I can’t be bothered to read through this, but it’s reminding me of two things.
    One is something I read recently about people thinking that the length of a
    second has changed, as they can’t seem to count seconds accurately by
    chanting “one-Mississippi, two-Mississippi, etc” any more.
    (The other will be in a separate post.)

    #1552877

    (As I suspected, it didn’t make it.)

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