Re: Unifying Atomic Time and the post-Gregorian calendar corrections

[Steve Allen]

Resurrecting a theme from long ago

On Thu 2003-07-03T19:54:11 +0100, Joseph S. Myers hath writ:
> On the effects of solar mass loss on orbital computations and definitions
> of units, and its (non-)detectability, see "Solar Mass Loss, the
> Astronomical Unit, and the Scale of the Solar System" by Peter D.
> Noerdlinger
> 
> (I can't now locate a good copy of this paper; that archived copy is
> missing images for many of the equations).

It now appears to be here
http://home.comcast.net/~pdnoerd/SMassLoss.html

--
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: Unifying Atomic Time and the post-Gregorian calendar corrections

[Joseph S. Myers]

On Thu, 3 Jul 2003, Markus Kuhn wrote:

> Fair enough. Though it would be academically interesting to see some
> discussion of what the contributing factors are for changes in the
> length of the tropical year. For length-of-day changes, we have have
> been told about tidal breaking and other effects. Are there similar
> theories for the long-term change of the Earth's orbit (change of solar
> mass, solar wind friction, etc.)?

On the effects of solar mass loss on orbital computations and definitions
of units, and its (non-)detectability, see "Solar Mass Loss, the
Astronomical Unit, and the Scale of the Solar System" by Peter D.
Noerdlinger

(I can't now locate a good copy of this paper; that archived copy is
missing images for many of the equations).

--
Joseph S. Myers
[EMAIL PROTECTED]

Re: Unifying Atomic Time and the post-Gregorian calendar corrections

[Steve Allen]

On Thu 2003-07-03T18:30:00 +0100, Markus Kuhn hath writ:
> Thanks for pointing this out! Weekday-continuity is indeed a bit of a
> problem of this approach. I can't see any other practical solution than
> skipping one weekday together with the skipped 29 February 5600, in
> other words, 5600-03-01 would be a Wednesday also in all the local
> civilian time zones.

It also deserves to be pointed out that the Julian Date would not
match in the two different calendrical schemes.  With that it becomes
tricky to calculate elapsed time.

> But then, they didn't have computer software to worry about during any
> of the past calendar reforms. I think user requirements might have
> changed for weekdays.

Are you willing to risk a fatwah if this is implemented and you are
identified as the one who proposed that a Friday will eventually
disappear from the calendar?

> According to
>
>   http://www.tondering.dk/claus/cal/node3.html#SECTION00322000
>
> astronomers such as John Herschel (1792-1871) and others suggested in
> the past to augment the Gregorian calendar with a rule that makes every
> year divisible by 4000 not a leap year. Similarly, the Orthodox church
> in Greece considered in the 1920s to replace the Gregorian "Y mod 400 =
> 0" rule with a "Y mod 900 in {200, 600}" rule. I'd be curious to hear,
> whether the usefulness of such proposals have ever been discussed more
> recently in the light of modern astrometric and orbital-modeling
> capabilities. Or do we first have to build a vast solar-system wide
> equivalent of GPS to gather data about the solar gravitation and
> pressure environment with sufficient accuracy for long-term forecasting?

Read the reference near the bottom of my Future of UTC page:
http://catless.ncl.ac.uk/Risks/17.86.html#subj10

Newcomb's mean longitude of the sun includes terms which naively
appear to be secular but which are actually the leading wave of
periodic changes.  That is why they should not be used even now, let
alone a long time from now.  Herschel did not have access to anywhere
near as many or as accurate a set of obsesrvations as Newcomb did.
There is no way to take Herschel's long term prediction for the
calendar seriously.

The deceleration of earth rotation is a secular term which we can be
sure will affect civil time.  On the contrary, I would be very
surprised to find anyone who would seriously contend that there are
any secular changes of the earth's orbit or obliquity which are
predictable enough to justify complicating the SRG's business.
Nevertheless, I'll ask around just to be more sure.

--
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: Unifying Atomic Time and the post-Gregorian calendar corrections

[Markus Kuhn]

Steve Allen wrote on 2003-07-03 16:15 UTC:
> Okay, but in the Caves of Steel where people use TI-based timekeeping
> 5600-03-01 is a Wednesday, and in the UT-based lands where the sun
> determines when people work and sleep 5600-03-01 is a Tuesday.

Thanks for pointing this out! Weekday-continuity is indeed a bit of a
problem of this approach. I can't see any other practical solution than
skipping one weekday together with the skipped 29 February 5600, in
other words, 5600-03-01 would be a Wednesday also in all the local
civilian time zones.

Otherwise, computers would not be able to calculate the day of the week
from a -MM-DD date without an extra table that keeps track of all
the rare (every 3000 years or so) exceptions to the Gregorian rule
triggered by British Time < TI - 11h overflow. Any need for software
functions that are tested only every 3000 years can safely be considered
bad practice.

I understand that none of the past calendar reforms did interrupt the
mod-7 weekday cycle. And references such as

  http://www.tondering.dk/claus/cal/node7.html#SECTION0074

argue even (through an absence of documented evidence to the contrary)
that the 7-day week might have been running uninterrupted for at least
the past 3000 years.

But then, they didn't have computer software to worry about during any
of the past calendar reforms. I think user requirements might have
changed for weekdays.

The Unix command "cal 03 5600" tells me today that 5600-03-01 will be a
Wednesday. It is also a form of long-term continuity that we stick to
that algorithm, no matter whether the Gregorian leap day 5600-02-29
actually took place or not.

> I am not convinced that there is anyone who does long-term solar
> system stability studies who would be willing and able to comment on
> this in an authoritative fashion.  It's just too far into the future.

Fair enough. Though it would be academically interesting to see some
discussion of what the contributing factors are for changes in the
length of the tropical year. For length-of-day changes, we have have
been told about tidal breaking and other effects. Are there similar
theories for the long-term change of the Earth's orbit (change of solar
mass, solar wind friction, etc.)?

According to

  http://www.tondering.dk/claus/cal/node3.html#SECTION00322000

astronomers such as John Herschel (1792-1871) and others suggested in
the past to augment the Gregorian calendar with a rule that makes every
year divisible by 4000 not a leap year. Similarly, the Orthodox church
in Greece considered in the 1920s to replace the Gregorian "Y mod 400 =
0" rule with a "Y mod 900 in {200, 600}" rule. I'd be curious to hear,
whether the usefulness of such proposals have ever been discussed more
recently in the light of modern astrometric and orbital-modeling
capabilities. Or do we first have to build a vast solar-system wide
equivalent of GPS to gather data about the solar gravitation and
pressure environment with sufficient accuracy for long-term forecasting?

Surely a government that feeds both a major space exploration agency and
a significant number of political representatives with close ties to
religious fundamentalism must be eager to fund research on when exactly
Easter will happen in the year 10 anno domini  ...

Markus

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

Re: Unifying Atomic Time and the post-Gregorian calendar corrections

[Steve Allen]

On Thu 2003-07-03T15:20:19 +0100, Markus Kuhn hath writ:
>   d) Whenever British Time is about to fall 12 h behind TI, UN/ITU/IERS (or
>  the Queen of England :) will write to all heads of government worldwide
>  and invite them to agree that the next year divisible by 400 shall not
>  be a leap year (except for anything living in TI or course) in all
>  countries.

> This will keep local times and TI from diverging by more than about a
> day or 25 h (for British Time the divergence will even be limited to
> about half a day or 13 h):
>
>  5496:   British Time = TI - 11h
>  5600-02-28: British time = TI - 11 h   (5600-02-29 skipped in civilian time)
>  5600-03-01: British time = TI + 13 h
>  5658:   British time = TI + 12 h
>  5814:   British time = TI + 11 h
>  5963:   British time = TI + 10 h

Okay, but in the Caves of Steel where people use TI-based timekeeping
5600-03-01 is a Wednesday, and in the UT-based lands where the sun
determines when people work and sleep 5600-03-01 is a Tuesday.

> This way, we have a time and calendar system with three nice properties:

The day of the week is one property Markus did not mention, and it is
a little bit weird.  Globetrotting travelers experience something like
this now when they fly through the day they might normally worship,
but at least they are allowed to use the same calendar in most places.

>   d) The spring equinox will (hopefully) remain more stable at the same
>  day of the year than if we kept UTC with the Gregorian calendar, because
>  the year length follows closer atomic time than the UT day length.
>  (On the last point, I'm still looking for confirmation from
>  astronomers with good knowledge of long-term prediction of the
>  longitude of the sun.) GOOD!

I am not convinced that there is anyone who does long-term solar
system stability studies who would be willing and able to comment on
this in an authoritative fashion.  It's just too far into the future.

If the other problems posed by UT vs.  TI are solved by a new
broadcast time system it should be sufficient, and not really
inconsiderate, to leave any equinox/calendar problem to posterity.

--
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

Unifying Atomic Time and the post-Gregorian calendar corrections

[Markus Kuhn]

I recently proposed in my posting "What to do if International Time hits
the International Date Line?" a new approach to solve two calendar and
time-keeping problems at the same time:

  a) the long-term deviation of atomic time from UT (i.e., in the years
 5658, 8462, ... the point where TI corresponds to local time crosses
 the international date line)

  b) the long-term deviation of the longitude of the sun from
 the Gregorian calendar date (i.e., after a few thousand years,
 the spring equinox will happen on 19 March, 18 March,
 17 March, ...)

The crucial idea/observation/hope is: while the daily rotation of the
earth deviates from atomic time strongly enough to cause an offset of
more than one day "relatively" soon, the annual rotation of the earth is
stable enough to remain in sync with atomic time within a day for many
ten thousand years to come.

This opens the possibility that the above two problems can be used to
cancel each other out. At least for the next few ten thousand years,
significantly longer than recorded human history!

It becomes clear from replies that I received that my last discussion
proposal wasn't really understood by many people.

So here is again in a nutshell "Kuhn's Atomic Calendar", a leap-second
free tiny improvement over the Gregorian Calendar:

  a) We adopt Temps International (TI) as suggested in Torino
 (TI = UTC in 2005, with no further leap seconds in TI, i.e.
  TI = TAI - 32 s forever).

  b) TI is what computers, navigation systems, time broadcasts, submarine
 crews, etc. will in the future use as the monotonic uniform international
 reference time (POSIX time_t, etc.) instead of today's UTC

  c) Where TI is converted into a broken-down time of the -MM-DD HH:MM:SS
 form, we strictly follow the Gregorian rules as specified in POSIX:2001,
 i.e. there is a 29 February if the year is a multiple of 4 unless
 it is a multiple of 100 unless it is a multiple of 400.

  d) For local civilian times, we need to change the offset to TI every few
 hundred years, because TI is detached from the rotation of the earth.
 This is no problem, because we change the offset between local civilian time
 and computer time already twice per year today for summer time, and
 countries keep hopping between time zones for political reason
 (see most recently Portugal's move to British time a few years ago).

 In other words:

  2005: British Time = TI
  2780: British Time = TI - 1h (from start of summer-time that year)
  3330: British Time = TI - 2h
  3712: British Time = TI - 3h
  ...
  5496: British Time = TI - 11h

 These changes would be implemented by skipping the deleted leap hour
 normally necessary to start summer time at the years listes above.

  d) Whenever British Time is about to fall 12 h behind TI, UN/ITU/IERS (or
 the Queen of England :) will write to all heads of government worldwide
 and invite them to agree that the next year divisible by 400 shall not
 be a leap year (except for anything living in TI or course) in all
 countries.

 We do this for the first time when we skip the Gregorian leap day
 5600-02-29 in all time zones. This would be handled in computers simply
 as a part of the normal locale-timezone database maintenance and would not
 even need recompiling of existing mainstream operating systems. It can also
 be easily announced 100 years in advance and when to do it will be
 obvious from even crude UT-TI forecasts.

This will keep local times and TI from diverging by more than about a
day or 25 h (for British Time the divergence will even be limited to
about half a day or 13 h):

 5496:   British Time = TI - 11h
 5600-02-28: British time = TI - 11 h   (5600-02-29 skipped in civilian time)
 5600-03-01: British time = TI + 13 h
 5658:   British time = TI + 12 h
 5814:   British time = TI + 11 h
 5963:   British time = TI + 10 h
 ...
 8332:   British time = TI - 11 h
 8400-02-28: British time = TI - 11 h
 8400-03-01: British time = TI + 13 h   (8400-02-29 skipped in civilian time)
 8423:   British time = TI + 12 h
 8513:   British time = TI + 11 h
 8601:   British time = TI + 10 h

This way, we have a time and calendar system with three nice properties:

  a) Computers etc. run on a strictly uniform, leap-second/hour/day-free,
 monotonic and predictable atomic Gregorian calendar (TI). GOOD!

  b) The offset between civilian local timezone and TI changes occasionally
 by one hour. NOT MUCH WORSE THAN TODAY!

  c) The maximal offset between between the TI used in computers and
 local civilian times will be limited all over the world to the
 range TI - 25h to TI + 25h (today: local times are in the range
 UTC - 13h to UTC + 13h or so). NOT MUCH WORSE THAN TODAY!

  d) The spring equinox wil