when’s the last time for kiddush levanah?

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.

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).

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.

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)

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)

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.

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!)

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

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

The online calendar is myzmanim.

“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.

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.

Does this go into the argument if efsher letzamtzem?

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.)

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.

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.

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

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.)