Re: Monsters from the id

2006-01-12 Thread Michael Deckers
   John Cowan wrote:

   [If TAI - 33 s were taken as the new basis for civil timescales, then]

  It is UTC that would be eliminated as the basis for local time.  It could
  be maintained for such other purposes as anyone might have.

   Yes, the IERS could maintain it as the timescale for a timezone
   whose local time approximates UT1 up to a second.

   Michael Deckers


Re: The real problem with leap seconds

2006-01-12 Thread David Malone
Yes: there is an order on the set of values of timescales -
it is a basic property of spacetime models that one can distinguish
past and present, at least locally. Spacetime is a differentiable
4-dimensional manifold, its coordinate functions are usually two
times differentiable or more. In particular, the set of values of
timescales does indeed have a topology (which is Hausdorff).

Sure - this is a reasonable definition of timescale, but I don't
think it is wide enough to include UTC. As I understand it, and
everyone will correct me if I'm wrong, UTC is not intended to be
directly related to spacetime coordinates at all. UTC is (currently)
an aproximation to the direction the earth is facing and is adjusted
according to how long it takes the earth to end up facing the same
direction again.

All of this is completely independent from the choice of a particular
calendar or of the time units to be used for expressing timescale values.

I'd agree with this for TAI (including that it should be the integral
of a nice 1-form), but I'm not so sure for UTC.

If you subtract a time from a timescale value, you get another
timescale value. If you mean to say that UTC takes its values in a
different space than TAI then you cannot agree with UTC = TAI - DTAI,
as in the official definition of UTC. And if you say that
UTC - TAI can be discontinuous (as a function of whatever)
with both UTC and TAI continuous then you must have a subtraction that
is not continuous. Strange indeed. Where did I misinterpret your post?

Yep - you've picked up my intent correctly. I'm saying that subtraction
is a stange operator taking a UTC value and a TAI value and gives
you something that's a real number.

The reason that I came to this conclusion is because none of the
documents I've read say that UTC can be expressed as a real number
- they all suggest it is expressed as labelled seconds. (For example,
see the way that Rec. 460-4 gives UTC values - I've never seen an
official looking document that tries to write UTC as a real.)

David.


Re: Monsters from the id

2006-01-12 Thread Mark Calabretta
On Thu 2006/01/12 02:36:44 CDT, John Cowan wrote
in a message to: LEAPSECS@ROM.USNO.NAVY.MIL

We already have that repeated time sequence and gap in much of the world,
and live with it.  These repetitions would be no better and no worse;
when a gap is present, the local sovereignty can omit the gap, but this
is not a necessary feature of the proposal.

At the start of daylight saving where I live the clocks are set forward
from 2am to 3am.  Naively it looks like there is a gap.  Likewise at the
end of daylight saving the hour from 2am to 3am appears to be repeated.

The apparent gaps and repeats are simply an artifact of what happens to
a clock display when you change it to read a different timescale.

Standard time Summer timeLegal time
     --
  2005/10/30 00:01:58 AEST (:   ):
  2005/10/30 00:01:59 AEST (2005/10/30 00:02:59 AEDT)   AEST
  2005/10/30 00:02:00 AEST  -  2005/10/30 00:03:00 AEDT  AEST/AEDT
 (2005/10/30 00:02:01 AEST) 2005/10/30 00:03:01 AEDTAEDT
 (:   ) 2005/10/30 00:03:02 AEDTAEDT
 (:   ) ::
 (:   ) ::
 (:   ) 2006/04/02 00:02:58 AEDTAEDT
 (2006/04/02 00:01:59 AEST) 2006/04/02 00:02:59 AEDTAEDT
  2006/04/02 00:02:00 AEST  -  2006/04/02 00:03:00 AEDT  AEST/AEDT
  2006/04/02 00:02:01 AEST (2006/04/02 00:03:01 AEDT)   AEST
  2006/04/02 00:02:02 AEST (:   ):
  :(:   ):

It should be clear that the gaps and repeats are fictitious, especially
if you think of AEST and AEDT as existing beyond the times when they are
in legal use.  Putting it in practical terms, suppose I have a traffic
accident at 0230 on 2006/04/02, what time will the police officer write
in his report?  For most times of the year he can omit the timezone spec
because there is no legal ambiguity, but to do so for this specific hour
would be insufficient, he must specify AEDT or AEST.

The situation with the proposed leap hour is quite different.  Given
that AEST is defined as UTC+1000, and AEDT as UTC+1100, would someone
care to speculate, in terms similar to the above, what will happen when
a leap hour is inserted?

Mark Calabretta
ATNF


Re: Monsters from the id

2006-01-12 Thread Rob Seaman
On Jan 12, 2006, at 12:36 AM, John Cowan wrote:No one, at least not on this list, is arguing for an alignment of theabsurd leap hour proposal (henceforth ALHP) with DST changes.I went rummaging through the ITU proposal and back as far as Torino.  Found this comment from a LEAPSECS thread on 28 July 2003: At Torino the proponents of omitting leap seconds supposed that the governments of the world might handle this situation using leap hours introduced into civil time by occasionally omitting the annual ``spring forward'' change to jump to summer/daylight time.This particular quote originated with Steve Allen's excellent page:  http://www.ucolick.org/~sla/leapsecs/dutc.htmlI couldn't find any explicit mention of this in the discussions at Torino, but Steve must have gotten it somewhere - and as you say, not from the list.  It may be an opportune time for folks to reread the presentations from Torino: http://www.ien.it/luc/cesio/itu/ITU.shtmlFor example, I found this interesting tidbit from the Russians: "This is to inform you that to our opinion it is necessary to preserve the status-quo of the UTC time scale."Considering GLONASS is always trotted out as the only explicit example of a system that fails to handle leap seconds, this seems significant somehow.More-or-less the entire text of the proposed change to ITU-R TF.460-6 is expressed here:Operational rules(after  UTC 21 December of the transition year)1   ToleranceThe difference of UT1 from UTC should not exceed ±1h.2   Adjustments to UTC2.1Adjustments to the UTC time-scale should be made as determined by the IERS to ensure that the time-scale remains within the specified tolerances.2.2The IERS should announce the introduction of an adjustment to the UTC time-scale at least five years in advance. At the time of the announcement the IERS should provide directions regarding the details of the implementation of the adjustment.2.3All operational rules and nomenclature prior to  UTC 21 December of the transition year given above no longer apply.NOTE 1 – The broadcast of DUT1 will be discontinued.NOTE 2 – Predictions of the Earth’s rotation currently indicate that such an adjustment would not be required for thousands of years.Note the inaccurate and self-serving "thousands of years" that is corrected to 500 years in the draft.  There isn't the slightest specification (or analysis) of how a leap hour might be implemented - just an assumption that the IERS will persist indefinitely.  We're certainly aware that "all operational rules" are to be changed - but what about the nomenclature?  Imagine changing an ISO or SI standard - preserving a trail of coherent nomenclature would be half the document.  And then, of course, the amazing fact that the document simultaneously increases the importance of DUT1 by orders of magnitude, while discontinuing its issuance.  This "proposal" is not only ill considered, it is simply - well - lazy and arrogant.We already have that repeated time sequence and gap in much of the world,and live with it.  These repetitions would be no better and no worse;when a gap is present, the local sovereignty can omit the gap, but thisis not a necessary feature of the proposal.The point I was trying to make is that you can't simultaneously omit the overlaps/gaps and preserve anything even vaguely resembling the familiar relationship between our clocks and the solar day.  It doesn't matter whether we continue an international civil time system or abandon it for local anarchy - people everywhere in the world would  have to deal with the repercussions.  That the situation will degrade slowly over a few hundred years before collapsing catastrophically doesn't really seem to recommend the plan.It may not sound like it, but I am willing to be convinced otherwise - but you'll have to do a lot better than rivaling the scant length of the ITU proposal.  How about a detailed scenario of exactly how you see this working for a couple of neighboring but distinct local timezones?  What is the precise mechanism that might be used?The subtext of both your position and the "absurd leap hour proposal" is that civil timekeeping is so trivial that everybody from barbers to burghermeisters should be encouraged to make public policy - after all, these aren't "important" scientific and technical issues.  Rather, civilian users deserve as good or better a timescale as the technical users (who ultimately can take care of themselves). Historians already deal with the discontinuity between Julian andGregorian calendars, which was similarly conducted in a decentralizedfashion between 1582 and 1924.That there was a global mess several hundred years in the past is not a particularly good reason to generate another global mess several hundred years in the future.Aliens?  Us?  Is this one of your Earth jokes?Rob SeamanNOAO

Re: Monsters from the id

2006-01-12 Thread John Cowan
Rob Seaman scripsit:

 I went rummaging through the ITU proposal and back as far as Torino.
 Found this comment from a LEAPSECS thread on 28 July 2003:

  At Torino the proponents of omitting leap seconds supposed that the
  governments of the world might handle this situation using leap hours
  introduced into civil time by occasionally omitting the annual ``spring
  forward'' change to jump to summer/daylight time.

This is definitely the PHK/JWC proposal rather than the ALHP: civil time
refers to local legal/business time.

 The difference of UT1 from UTC should not exceed ±1h.

This, however, clearly is the ALHP.

 The point I was trying to make is that you can't simultaneously omit
 the overlaps/gaps and preserve anything even vaguely resembling the
 familiar relationship between our clocks and the solar day.

The relationship between our clocks (legal time clocks, the only kind
I am concerned with) and the solar day is very weak, as I have established
over and over.  If local  is the middle of the night, the practical
requirements of legal time are pretty much satisfied.

 people everywhere in the world
 would  have to deal with the repercussions.  That the situation will
 degrade slowly over a few hundred years before collapsing
 catastrophically doesn't really seem to recommend the plan.

There will be no catastrophic collapse, just a gradual local adjustment
as needed.

 It may not sound like it, but I am willing to be convinced otherwise
 - but you'll have to do a lot better than rivaling the scant length
 of the ITU proposal.  How about a detailed scenario of exactly how
 you see this working for a couple of neighboring but distinct local
 timezones?  What is the precise mechanism that might be used?

A sovereign country will notice that there is too much discrepancy
between solar time and legal time to be comfortable: perhaps kids are
waiting for school buses in the dark, as happened in the U.S. in 1974.
The country will then adjust its legal time, perhaps in coordination
with its neighbors, perhaps not.

 The subtext of both your position and the absurd leap hour proposal
 is that civil timekeeping is so trivial that everybody from barbers
 to burghermeisters should be encouraged to make public policy - after
 all, these aren't important scientific and technical issues.

Those who want UT1 or TAI know where to get it.

 Rather, civilian users deserve as good or better a timescale as the
 technical users (who ultimately can take care of themselves).

Good for what?  (This is not a rhetorical question.)

 Aliens?  Us?  Is this one of your Earth jokes?

No.

--
John Cowan  [EMAIL PROTECTED]  www.reutershealth.com  www.ccil.org/~cowan
The known is finite, the unknown infinite; intellectually we stand
on an islet in the midst of an illimitable ocean of inexplicability.
Our business in every generation is to reclaim a little more land,
to add something to the extent and the solidity of our possessions.
--Thomas Henry Huxley


Re: Monsters from the id

2006-01-12 Thread John Cowan
Rob Seaman scripsit:

 And the point I'm making is that you can't shift timezones at will to
 accomplish this without creating seams in legally realized time.

We already have seams in legally recognized time.

 Just making the dark stay put would result in ambiguous
 timekeeping.  Daylight saving time layered on solar locked standard
 time is a different thing from attempting to use an overtly similar
 mechanism to compensate for the misappropriate substitution of
 interval time for solar time.

Stripped of the adjectives, why is it different?

 What starts out as gradual (also known as ignored completely)
 will end in the same familiar quadratic rush.  Nothing about your
 notion mitigates this.

In the end, it will be impossible to maintain the notion that a solar
day is 24h of 60m of 60s each: we wind up, IIRC, with the solar day
and lunar month both at about 47 current solar days.

 1) provide a system for uniquely sequencing historical events

Haven't got that now.

 2) allow events in distant lands to be compared for simultaneity

We have that now, but it takes a computer to keep track of all the
details in the general case.

 3) avoid disputes over contractual obligations

That's done by specifying the legal time of a given place.  If I agree
to meet you under the Waverley at noon 13 March 2020, it's all
about what the U.S. Congress says legal time in New York City is
as of that date -- which is not predictable in advance.  (You will also
have a problem finding the Waverley, unless you are an old New Yorker.)

 4) minimize the potential for political disagreements

Good luck.

 5) satisfy religious requirements

Out of scope.

 6) keep it dark near 00:00 and light near 12:00

Agreed.

 7) support educational goals (Yes Virginia, the universe actually
 makes sense.)

No problem.

 8) allow coal miners to aspire to be amateur astronomers

Eh?  I am not recommending abolishing UT1, though it seems strange to
me to measure angles in hours, minutes, and seconds instead of in
radians like a proper SI-head.  (Fourteen inches to the pound, oh Bog!)

 9) permit the construction of sundials - public clocks with no moving
 parts

Sundials don't show legal time or even a good approximation of it much
of the time.

 10) tie an individual's first breathe on her first day to her last
 breathe on her last day

Where's the problem here?  Any timescale can do that, even the Mayan Long Count.

--
John Cowan  [EMAIL PROTECTED]  www.reutershealth.com  www.ccil.org/~cowan
The whole of Gaul is quartered into three halves.
-- Julius Caesar