[LEAPSECS] Skepticism

[Rob Seaman]

It's good to be skeptical of the status quo.  The bar to meet is even higher for *changes* to the status quo.  Best practices of system engineering exist precisely to answer questions from skeptics.  The draft revision to TF.460 is an example of "worst practices" - whatever one thinks of the merits of its notional position.

On Dec 30, 2010, at 9:04 PM, Jonathan E. Hardis wrote:


> On Dec 30, 2010, at 7:41 PM, Rob Seaman wrote:

> 

>> It is *hasty* to force a decision when the current definition of UTC is viable for centuries.

> 

> ... There are those who believe that the current definition of UTC isn't viable TODAY.


What does this mean?  I don't mean the question of "belief", since humans are capable of remarkable feats in that regard.  But rather, focus on "viable" and "today".  I've appended Bulletin C 40.

We know that there will not be a leap second for (at least) the next six months.  We've known this for (about) the last six months.  That's a current look-ahead window of a year.  There is thus no difference between the UTC status quo and the draft revision (as inferred from smoke and mirrors) today or for the next 180 (or so) tomorrows.  No difference aside from a requirement to determine and announce DUT1, which is the baby being thrown out with the leap second bath water.

I've also appended Bulletin D 107.  Bulletin D is advisory in the sense that it describes data that is more directly supplied through other means ("the value of DUT1 to be disseminated with the time signals").  That said, it has often proved useful for my own purposes.


>> As someone else points out, it is quite possible to break international civil timekeeping to the point that all the King's men can't put it back together again.



> ... That is, in this simplified model, we would need slightly less than 1 leap second per year until 2017, at which point we would need slightly more than 1 leap second per year.  [...]


I've elided the algebra since it seems a distraction - as does the artificially precise value of "2017".  Leap seconds have been accumulating at about 1 per year-and-a-half.  This has been expected to accelerate quadratically (because it is a cumulative effect derived from the relative rates).  This has recently been observed to be slower.  The current mechanism is flexible enough to handle this natural variability.


> Okay.  Let's presume that (1) up until the beginning of 2011 we added leap seconds such that DUT1 was 0, (2) for the sake of early 21st century technology, we stopped declaring leap seconds for 40 years, until 2051, and (3) everyone was put on notice that starting in 2051 there would be two leap seconds per year (say, June and December), each and every year, for at least 300 years.


What is the advantage of waiting 40 years?  Do we believe that during this 40 year hiatus that programmers and system engineers would be building leap second support into their systems and code in preparation for the ITU to recognize the error of their ways?


> In this model, DUT1 would be about 43 seconds in 2051.  Then, after the reimposition of leap seconds, DUT1 would decrease every year until it reached a minimum of -22 seconds at about 2210, after which it would then increase to about 27 seconds in 2350.


For the sake of argument.  But what this really demonstrates is the need for a mechanism to distribute DUT1 "for the sake of early 21st century technology", and the utter lack of such in the draft revision.


> The world at large ca. 2300 would have to decide what to do next -- how many leap seconds per year, starting when.   And let's give them credit for being able to make such a decision for themselves.


I'd like to be able to give their grandparents credit for being able to plan ahead.

What is really being handed to the future deckhands of spaceship Earth in 2051 and 2350 is a fait accompli of this significantly larger DUT1 with no way to introduce an immediate correction without an oddball intercalary event:

	"Ok, everybody reset your microwaves and
	coffee pots by 43 seconds on New Year's Eve.
	Don't ask us why - just do it!  Trust us.
	No, really.  No, really, this isn't a bad joke.
	My Mama?  Your Mama!"

Rather than being able to make such an unattractive decision for themselves, they get to introduce a large unphysical ramp (in one direction or the other - in your scenario of 2 seconds per year) for year after year to catch up with the synodic day.


> The point is, there is a distinct advantage to regularity and predictability in leap seconds -- which you could get in trade by giving up on keeping DUT1 to less than 0.9 seconds.


I'm baffled.  Nobody here has opposed improvements in leap second scheduling.  (We've explored this in great detail - see the archives.)  ...and more to the point, nobody on the ITU team has ever floated such a trial balloon.

As has been pointed out time-and-again, such improvements could be implemented without changing the current wording of TF.460.  If the 0.9s limit on DUT1 has to be relaxed, perhaps the language would require a minor revision.  My reading of TF.460-4 is that the limit could lengthened to +/- 3.0 seconds (30 emphasized ticks each way) without sacrificing the actual *radio* mechanism (that it seems to me is the only thing truly in the purview of ITU-R).  Even if the limit grows beyond that, some new convention could permit the new limit to function - perhaps even with the verbatim current wording if DUT1 were clarified to be some composite value summing the radio correction with some new internet delivered value.

Which is all to say that the current wording is extremely flexible.  What isn't flexible is the fundamental identification of civil time with the synodic day.  Leap seconds are a means to an end.  Don't sacrifice that end just to achieve some imagined self-serving short term goal.

From the top:

1) We have been unable to brainstorm productively on improvements to leap second scheduling since for more than a decade we have been obligated to fend off time-and-again this monomaniacal and unphysical "project" to get rid of them completely.  The original GPS World piece proffered five alternatives.  Four have been ignored utterly.

2) Nobody here opposes the idea of improving the scheduling algorithm, perhaps permitting the announcement of the equivalent of Bulletin C several years in advance.

3) A new-and-improved 21st century mechanism to replace Bulletin D is required now (when DUT1 is kept small) and will be vastly more important should DUT1 be allowed to grow (under any scenario).

Let's table any ITU actions for 2012.  Let's schedule one or more meetings to wrestle with the issues above.  Let's stop trying to ram through a decision without building consensus.  It is not the astronomers here who are unwilling to entertain creative new solutions.  We will continue to oppose uncreative non-solutions.

Rob
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Begin forwarded message:


> From: IERS EOP Product Center <services.iers at obspm.fr>

> Date: July 16, 2010 2:01:24 AM MST

> To: bulc.iers at obspm.fr

> Subject: Bulletin C number 40

> 

> 

> 

> 

>     INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS) 

> 

> SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE ET DES SYSTEMES DE REFERENCE

> 

> 

> SERVICE DE LA ROTATION TERRESTRE

> OBSERVATOIRE DE PARIS                                   

> 61, Av. de l'Observatoire 75014 PARIS (France)

> Tel.      : 33 (0) 1 40 51 22 26

> FAX       : 33 (0) 1 40 51 22 91

> Internet  : services.iers at obspm.fr

> 

>                                               Paris, 14 July 2010

> 

> 

>                                               Bulletin C 40

> 

>                                               To authorities responsible                   

>                                               for the measurement and 

>                                               distribution of time             

> 

> 

> 

>                          INFORMATION ON UTC - TAI

> 

> 

> NO positive leap second will be introduced at the end of December 2010.

> The difference between Coordinated Universal Time UTC and the 

> International Atomic Time TAI is :		

> 		

>     from 2009 January 1, 0h UTC, until further notice : UTC-TAI = -34 s

> 

> Leap seconds can be introduced in UTC at the end of the months of December 

> or June,  depending on the evolution of UT1-TAI. Bulletin C is mailed every  

> six months, either to announce a time step in UTC, or to confirm that there 

> will be no time step at the next possible date.

> 

> 

>                                             Daniel GAMBIS

>                                             Director			

>                                             Earth Orientation Center of IERS

> 					     Observatoire de Paris, France

> 

> 

> __________________________________________


Begin forwarded message:


> From: IERS EOP Product Center <services.iers at obspm.fr>

> Date: November 30, 2010 6:25:22 AM MST

> To: buld.iers at obspm.fr

> Subject: Bulletin D

> 

>  INTERNATIONAL   EARTH   ROTATION AND REFERENCE SYSTEMS  SERVICE   (IERS) 

> SERVICE INTERNATIONAL DE LA ROTATION  TERRESTRE ET DES SYSTEMES DE REFERENCE

> 

> 

> SERVICE DE LA ROTATION TERRESTRE

> OBSERVATOIRE DE PARIS                                   

> 61, Av. de l'Observatoire 

> 75014 PARIS (France)

> Tel. 33 (0) 1 40 51 22 26  

> FAX  33 (0) 1 40 51 22 91

> Internet: services.iers at obspm.fr                   Paris, 30 November 2010

> 

>                                                   Bulletin D 107

> 

> 

> 

> 

>                               ANNOUNCEMENT OF DUT1

> 

> 

>        From the

> 

>                           6 January 2011, 0h UTC

> 

>    until further notice, the value of DUT1 to be disseminated with the 

>    time signals will be

> 

> 

>                                  DUT1 = -0.2 s

> 

> 

>        Bulletin D 108 should be issued in February 2011

> 

> 

> 

> 

>