Re: [LEAPSECS] it's WP7A week in Geneva
In message ab352dd8-ffdb-4ccf-a582-c7db12163...@noao.edu, Rob Seaman writes: I have (tediously, bombastically, endlessly) asserted that civil time IS solar time. This is a statement of requirements. Requirements describe the problem space. And you have repeatedly tried to ignore the question of how large the civil-solar tolerance is, can or should be. I would estimate that the majority of the worlds population are not within one hour of solar time at any point in the year. China, for instance, is one single timezone. But maybe part of that problem is in the moniker civil time, which we have never fully agreed what means ? How about we operate with _three_ kinds of time and one kind of geophysics: Timekeeping Time: What timekeeping scientists work with, for keeping time. Mind you: Time, not 'Earth Orientation. Today this would be TAI, TAL etc. Earth Orientation: A set of physical parameters describing the motion of this planet, including its rotation. Today this would be UT, UT1, UT2, and half of UTC. Scientific/Technical Time: What computers and scientific experiments use internally, in order to be able to communicate temporal relationships unambiguously. Today this is UTC + Leap-second table + Leap-second announcement. Human time: What people see on their clock. Today that is usually UTC, fuzzed by political concepts such as DST. Obviously, Neither ITU nor BIPM has any control over what Human Time is or how it works. National and federal lawmakers decide that, often illadvisedly, and occationally very stupidly. China, as I recall, is one single timezone, and some places countries have 30 minute offsets from UTC I belive. If any national government wants to do something stupid to human time in their country, nobody can prevent them from doing so. Timekeeping Time and Earth Orientation should be left to the scientists, and should obviously be established and maintained as precise as funding will allow. UN and ITU has no mandate in this area, so the relevant organizations (IAU etc) are free to do as they please. What is left then, is the Scientific and Technical time. Which is exactly what UTC was intended to be originally, and why the definition and possible redefinition of UTC happens in an obscure technical corner, of a UN organ most people have not heard about. Now, please make your argument, that Scientific and Technical time should be polluted by earth orientation parameters ? Yes, it would be convenient for astronomers pointing their telescopes, but do you have any other argument than that ? Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] it's WP7A week in Geneva
Poul-Henning Kamp wrote: And you have repeatedly tried to ignore the question of how large the civil-solar tolerance is, can or should be. I don't think a fair and impartial witness would say given my plethora of messages over the years that I've ever successfully ignored anything :-) That said, a one-hour tolerance is many orders of magnitude too large, see previous threads. But maybe part of that problem is in the moniker civil time, which we have never fully agreed what means ? What I mean is the common international timescale that underlies local time worldwide for everyday purposes. How about we operate with _three_ kinds of time and one kind of geophysics: Certainly one geophysics - that's the point of tying the standard to physical reality rather than to racks of equipment demanding constant attention and robust interconnects forever. There are many more than three kinds of time, but I believe previous discussions have uncovered no reason for layering the civil timekeeping standard and infrastructure on more than the two that UTC already references. There are plenty of degrees of freedom to find alternate solutions that actually address the requirements. If any national government wants to do something stupid to human time in their country, nobody can prevent them from doing so. Which is why underlying physical reality has to fill that role. Also, what exactly would an isolated human time in their country actually mean? Every day for everyone, our activities are connected to those of humans and systems in other time zones. There is one international community and there must be one common timescale. astronomers pointing their telescopes, but do you have any other argument than that ? As stated many times, astronomers are power users for more kinds of time (in more bizarre places) than anybody else. We certainly use both atomic and mean solar timescales. This discussion is about civil timekeeping. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] it's WP7A week in Geneva
Tony Finch wrote: India is a prominent example of a half hour timezone offset. (Sorry for straying off topic.) Indeed. I reset the second clock on my phone to the timezone of New Delhi when my daughter had a semester in Dharamsala. It's been a couple of years and I've never set it back. It is precisely the fact of a international civil timescale that makes the timezone system work. In return, the many timezones and numerous special cases represent constraints on the common underlying standard to better track mean solar time. (Not off topic at all.) Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] it's WP7A week in Geneva
Richard B. Langley wrote: Quoting Rob Seaman sea...@noao.edu: It's impressive that civil GPS discussions reach back through so many meetings. Any idea when the 1st CGSIC meeting was held? Probably 1986: Cool. Thanks! Proceedings of the 1991 National Technical Meeting of the Institute of Navigation January 22 - 24, 1991 Sheraton San Marcos Hotel Phoenix, AZ Argh! Another meeting I could have attended easily if I only knew it existed. GPS as a project dates back to the mid-70's, right? Started in 1973. With completion in the early 90's? How do you define completion? Reaching FOC (full operational capability)? Then, July 17, 1995. Even a bit longer than I thought. So it took GPS 22 years and they're still talking about it 14 years after that. We've only been talking since 1999. We have 26 years to go! Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] it's WP7A week in Geneva
On Thu, 10 Sep 2009, Rob Seaman wrote: It is precisely the fact of a international civil timescale that makes the timezone system work. Yes. In return, the many timezones and numerous special cases represent constraints on the common underlying standard to better track mean solar time. The constraints from timezones aren't tight enough to make any diffence to leapseconds. For civil time the key requirement is that everyone agrees, which is why timezones are wider than a second. The situation in Xinjiang is a good example, because the argument over how to set the clocks is entirely political and makes little practical difference to things like business opening hours. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ GERMAN BIGHT HUMBER: SOUTHWEST 5 TO 7. MODERATE OR ROUGH. SQUALLY SHOWERS. MODERATE OR GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] it's WP7A week in Geneva
M. Warner Losh wrote: There are a number of solutions to the current leap-seconds problems that don't completely decouple UTC from the sun. As well as non-solutions like leap-hours that don't actually eliminate leap-seconds, but rather accumulate them for later release in one colossally indigestible lump. There's some that do in the recognition that UTC really is going to be viable at most a few hundred to a few thousand years anyway due to the quadratic acceleration of leap second timing. The quadratic acceleration will apply to any proposed solution relative to atomic timescales where the second is of a fixed length. This issue is not specific to the current UTC. In particular, it is not addressed at all by the proposal to embargo leap-seconds. Anyway, as with all engineering issues, the practical problems should be discussed as widely as possible, and the real requirements for the system should be continually reevaluated to ensure that the system is meeting the real needs of its users. Amen! And with engineering best practices, no single power bloc should seek to force adoption of their preferred option. We would have gotten much more done (and I would have written many fewer messages to everyone's benefit :-) over the past 10 years if there weren't a need for constant vigilance to fend off incessant attempts to hurry a decision. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] it's WP7A week in Geneva
In message: de4e112b-d8da-4e92-9458-ea89c8dbc...@noao.edu Rob Seaman sea...@noao.edu writes: : M. Warner Losh wrote: : : There are a number of solutions to the current leap-seconds problems : that don't completely decouple UTC from the sun. : : As well as non-solutions like leap-hours that don't actually eliminate : leap-seconds, but rather accumulate them for later release in one : colossally indigestible lump. Actually, that solution does keep UTC coupled to the sun. I tend to agree that large adjustments like that would never happen. But any insertion of time into the time scale would : There's some that do in the recognition that UTC really is going to : be viable at most a few hundred to a few thousand years anyway due : to the quadratic acceleration of leap second timing. : : The quadratic acceleration will apply to any proposed solution : relative to atomic timescales where the second is of a fixed length. : This issue is not specific to the current UTC. In particular, it is : not addressed at all by the proposal to embargo leap-seconds. Actually, it *IS* addressed by the embargo on leap seconds. The idea there would be to publish the UT1 and not worry that it grows without bound. Then you don't have to coordinate the insertion of leap seconds, just publish a measurement that says what the delta is. What isn't addressed is keeping them in sync. They are two different things, and we shouldn't lose sight of that fact. And embargo on leap seconds forever is exactly the same thing as saying UTC is no longer tied to the sun. That's a change that should be considered, even if it ultimately proves to be not a viable change. This is a proposed solution, and one that may have merit. However, only if the users of time for which it actually matters that DUT1 is 1s can get the larger corrections from somewhere else, retool, etc. These costs may be smaller than continued insertions of leap seconds (they could very well be larger too: nobody has done a public, comprehensive study here). : Anyway, as with all engineering issues, the practical problems : should be discussed as widely as possible, and the real requirements : for the system should be continually reevaluated to ensure that the : system is meeting the real needs of its users. : : Amen! : : And with engineering best practices, no single power bloc should seek : to force adoption of their preferred option. We would have gotten : much more done (and I would have written many fewer messages to : everyone's benefit :-) over the past 10 years if there weren't a need : for constant vigilance to fend off incessant attempts to hurry a : decision. Correct. Unfortunately, the power block that was in control in the late 60's and early 70's has shifted now so that the relative importance of each of the factions has changed. The importance for various factors going into the leap-second decision has changed. The biggest one is now almost all terrestrial navigation is done with GPS and the DUT1 error correction no longer matters since people don't do things by hand anymore. Yet the fundamental solution hasn't. If there had been no action, no leap seconds, etc invented to harmonize the atomic and civil time scales (this would go back into the late 50's), then we'd come up with a different solution today because the playing field is so radically different. Some say different enough to pay the penalty of disturbing the status quo, others are not so sure so there's friction between the different groups. This tends to lead to preservation of the status quo. The current stalemate likely won't change until a plane crash can be tied to leap seconds... Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] it's WP7A week in Geneva
On Wed 2009-09-09T23:49:42 +, Poul-Henning Kamp hath writ: In message e44632d3-66d3-47d3-8b7a-7d8e7245d...@noao.edu, Rob Seaman writes: Why leap seconds are difficult to get right for an equipment vendor Sam Stein, Symmetricom, Inc. I hope the presentations will be posted online. Ask him ? Sam has been very friendly responsive in the past. The CGSIC presentations are often posted to the web. I welcome the presentation by Sam Stein and look forward to seeing it. It has the possiblility of addressing one of the big lacunae in the whole story of UTC and abandoning leaps: Who are the stakeholders and what problems are they having? The atomic chronometer keepers have been insisting that there is some urgent need to avoid leap seconds, and to avoid more time scales, but they do not name names, they do not give examples, they simply repeat that assertion, sometimes along with the spectre of planes crashing which was first aired 40 years ago. As they say on the USENET (or is that blogosphere now?) cite or shite. Without the cite it is clear that the BIPM temporal hegemony is threatened, but it is not clear how much the rest of the world should care. What the CCIR did demonstrate by their action in 1970, and the IAU (by redefining UT1 twice in the past 30 years), and the UK Admiralty (changing GMT by twelve hours) is that a time scale defined by somebody else can be changed at their whim to have characteristics which are no longer compatible with previous uses. So the natural response from everyone whose new operational system needs an operational time scale is to say If we use their scheme we're just SOL, for they may change it at any time in a way that breaks our system, so why not define a new time scale that suits us? The only thing in the favor of the current ITU-R structure is that this time it has been so diplomatically circumspect that there may be no organization which could hold the current UTC definition in a condition safer against any kind of change. This has become an Us vs. Them situation instead of a We the people situation -- all of the people, not just the physicists, not just the astronomers, not just the navigators, and not just us here now, but looking forward to secure things for our posterity. I have to suppose some leadership of that sort was present, privately, while Klepczynski acted for US DoS as he got the Galileo folks to agree to change the specified time scale for the EU navigation satellites from the original TAI to GPS time. That sort of leadership and diplomacy is not evident openly in the ITU-R process. But having typed this I seem to have echoed a Canadian actor playing a 23rd century starship captain reciting an 18th century US document on a devastated planet. This is way too Kirk-like for me, where's Spock? -- Steve Allen s...@ucolick.orgWGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99855 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
