Re: Time after Time

2005-01-24 Thread Markus Kuhn
John Cowan wrote on 2005-01-23 18:37 UTC:
 Markus Kuhn scripsit:

  UTC currently certainly has *no* two 1-h leaps every year.

 There seems to be persistent confusion on what is meant by the term
 leap hour.

Why?

 I understand it as a secular change to the various LCT offsets,
 made either all at once (on 1 Jan 2600, say) or on an ad-lib basis.

No. A UTC leap hour is an inserted 60-minute repeat segment in the UTC
time scale, which starts by jumping back on the UTC time scale by one
hour. This has been proposed by BIPM in Torino to be done for the first
time to UTC in about 2600, instead of doing the about 1800 leap seconds
that would be necessary under the current |UTC - UT1|  900 ms until
then. The proposed UTC leap hour simply means that the definition of
UTC is relaxed to (something like) |UTC - UT1|  59 min, and the size of
the adjustment leap is increased accrodingly from 1 s to 3600 s.

Local civilian times are of no convern to ITU, as they are entirely the
responsibility of numerous national/regional arrangements.

 You seem to be using it in the sense of a 1h secular change to universal
 time (lower-case generic reference is intentional).

I can't understand what could be ambiguous here. A leap hour means to
turn a clock forward or backward by an hour. We have done it twice a
year in many LCTs. The BIPM suggested in Torino that we should do it
every couple of hundred years to UTC as well, which would become
permissible by going from the rule |UTC - UT1|  900 ms to a relaxed
rule such as |UTC - UT1|  59 min.

The term leap hour does in no way imply what time zone/scale we are
talking about, and in this context we are talking mostly about UTC.

[How a UTC leap hour would affect LCTs is up the maintainers of the
these LCTs. Since the LTCs currently in use have their leap hours on
many different days of the year, a UTC leap hour would mean that at
least some LCTs would have three leap hours in that year. This could
only be avoided if all LCTs would agree to do their DST leaps
simultaneously with the UTC leap.]

In summary: There are basically three proposals on the table:

  a) Keep UTC as it is (|UTC - UT1|  900 ms) and just make TAI more
 widely available in time signal broadcasts

  b) Move from frequent UTC leap seconds to far less frequent UTC leap
 hours, by relaxing the UTC-UT1 tolerance (e.g., |UTC - UT1|  59 min)

  c) Remove any future leap from UTC, such that UTC becomes TAI plus a fixed
 constant (i.e., |UTC - UT1| becomes unbounded and will start to grow
 quadratically). In this scenario, LCTs would have to change their
 UTC offset every few hundred years, to avoid day becoming night
 in LCTs.

My views:

  a) is perfectly fine (perhaps not ideal, but certainly workable)

  b) is utterly unrealistic and therefore simply a dishonest proposal
 (UTC is so popular today in computing primarily because it is
 *free* of leap hours)

  c) I could live with that one, but what worries me is that
 it will create a long-term mess in a few millenia, when
 |UTC-LCT|  1 day. I am annoyed that this long-term mess and solutions
 around it are not even being discussed. (My hope would have rested
 on resolving the |UTC-LCT|  1 day problem by inserting leap
 days into the LCTs every few thousand years as necessary, to keep
 |UTC-LCT|  36 hours this way, and that these leap days in LCTs could
 perhaps be the same that may be necessary anyway every few
 millenia to fix the remaining Easter drift in the Gregorian
 calendar:
 http://www.mail-archive.com/leapsecs@rom.usno.navy.mil/msg00206.html )

Markus

--
Markus Kuhn, Computer Lab, Univ of Cambridge, GB
http://www.cl.cam.ac.uk/~mgk25/ | __oo_O..O_oo__


Re: two world clocks AND Time after Time

2005-01-24 Thread Poul-Henning Kamp
In message [EMAIL PROTECTED], Tom Van Baak writes:

Another observation is that our local newspaper always
prints Sun and Moon rise and set times. But not time
of noon. Why is this? Maybe it's just our paper (noon
implies sun and we don't see much of it here in Seattle).

Why is the instant of sunrise or sunset of popular value
while the high point of noon isn't. What does this suggest
about the risk of allowing noon to wander an hour over
the span of 1000 years?

Several countries have codified sunrise and sunset as when
traffic needs to light up.  In Denmark while cars and
motorbikes are lit up at all times, bicycles and horses
must be lit up from sunset to sunrise.  There are similar
rules for vessels on water I belive.

 Month is entirely conventional in its meaning.
 Year is entirely conventional in its meaning.
 So soon day will be entirely conventional in its meaning.

Can you explain this more? I can see how Month
would be conventional, or even entirely conventional
but are year and day also such extreme cases?

The Year represents when the constellations repeat their performance,
but the precision of this is wrecked by the leap-years, so it is
only conventional these days.

It seems to me the popular understanding of a year
is accurate to +/-1 day. And the popular understanding
of noon is accurate to +/- 1 hour or two. Does that make
them entirely conventional?

Seen from an astronomical point of view: yes, you can't point your
telescope with it.

 The trick will be to educate the general public that 12:00 means
 slightly less about where the sun is in longitude than the Gregorian

Sure, but it seems to me - regardless of the timezone,
regardless of daylight saving time, regardless of the
season, regardless of latitude, to the general public
12:00 means lunchtime (or their VCR got unplugged).
The sun doesn't have much say about it.

Fully agreed.

I would even venture to claim that a lot of todays teenagers are
only mildly aware of the noon -- more light outside connection :-)

--
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
[EMAIL PROTECTED] | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.


Re: two world clocks AND Time after Time

2005-01-24 Thread Steve Allen
On Mon 2005-01-24T00:50:10 -0800, Tom Van Baak hath writ:
 Isn't knowing when noon is already a specialist operation?
 I mean, most people could tell you when noon is to within
 an hour or two or three, but finer than that requires a far
 amount of daily mental calculation, no?

Noon has long required a calendar, an almanac, a longitude, and the
ability to perform addition and subtraction.  This has long been
something that could be presumed within the abilities of any locality
big enough to call itself a town.  The tasks of business, payroll,
and banking demand that much.

Sunrise and sunset have required haversines.  That's why the
newspapers publish them.  Trigonometry was not required for simple
civil life.

--
Steve Allen  UCO/Lick Observatory   Santa Cruz, CA 95064
[EMAIL PROTECTED]  Voice: +1 831 459 3046 http://www.ucolick.org/~sla
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E49 89 0E FE 26 B4 14 93


Re: Time after Time

2005-01-24 Thread Poul-Henning Kamp
In message [EMAIL PROTECTED], Markus Kuhn writes:

You surely must have seen my detailed UTS proposal for how UTC leap
seconds should be handled trivially and safely by the overwhelming
majority of computer applications, without any special considerations
whatsoever by normal application programmers:

  http://www.cl.cam.ac.uk/~mgk25/time/leap/utc-torino-slides.pdf
  http://www.cl.cam.ac.uk/~mgk25/uts.txt

Markus, that's all very nice and cute, but it is a grusome hack and
should not be propagated.

It is less gruesome than what we have now in the NTP code, but it
is still a gruesome hack.

There are far to many problems in this that you don't consider:

1) Computers booting inside your 1000 second interval do what ?

2) What about a computer being offline (by design or accidentally)
   during the 1000second window ?

3) Many real time systems will not tolerate 1e-3 clock error.

4) How wold a leap-time aware application run on such an operating
   system ?

5) You still need to way to distribute leapseconds to embedded and
   offline computers.


Your proposal pastes over some of the minor issues with leap seconds,
but it doesn't address the two fundamental problems:

   1. You don't know when they will happen with long enough warning.

   2. You can't test one when you need to.

--
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
[EMAIL PROTECTED] | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.


Re: two world clocks AND Time after Time

2005-01-24 Thread Poul-Henning Kamp
In message [EMAIL PROTECTED], Steve Allen writes:
On Mon 2005-01-24T00:50:10 -0800, Tom Van Baak hath writ:
 Isn't knowing when noon is already a specialist operation?
 I mean, most people could tell you when noon is to within
 an hour or two or three, but finer than that requires a far
 amount of daily mental calculation, no?

Noon has long required a calendar, an almanac, a longitude, and the
ability to perform addition and subtraction.

You forget a lawyer or at least a copy of the relevant laws in your
area, because surely you're not assuming that my watch runs on UTC ?

--
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
[EMAIL PROTECTED] | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.


Re: two world clocks AND Time after Time

2005-01-24 Thread John Cowan
Steve Allen scripsit:

 What we are being told by the Time Lords is that, starting from a date
 in the near future, knowing when noon is will also be a specialist
 operation.

Already true.

For many months of the year, solar noon is closer to 1 PM, or even 1:30
PM, in a great many countries, and how many people actually realize
*that*?

--
Winter:  MIT,   John Cowan
Keio, INRIA,[EMAIL PROTECTED]
Issue lots of Drafts.   http://www.ccil.org/~cowan
So much more to understand! http://www.reutershealth.com
Might simplicity return?(A tanka, or extended haiku)