Re: [LEAPSECS] civil-solar correlation with TI
On Tue, 23 Dec 2008, Zefram wrote: > > Either of my scenarios still suffers from the problem that the TI-UT > difference accelerates. These timezone offset changes would be needed > at decreasing intervals. By the time timezones are jumping by an hour > every year, one might expect to see political pressure for a new scheme. > But I don't think anything would put a stop to the process before then. My tonge-in-cheek "sunrise time" idea copes quite well with the far future. Because it becomes normal to change timezone most days, it becomes easy to absorb rate differences between atomic time and solar time even if they are as large as several seconds per day. The main problem would then be running out of digits in the standard timezone offset field... Tony. -- f.anthony.n.finchhttp://dotat.at/ FAEROES SOUTHEAST ICELAND: SOUTHWESTERLY 6 TO GALE 8, OCCASIONALLY SEVERE GALE 9 IN SOUTHEAST ICELAND. VERY ROUGH OR HIGH. RAIN OR SHOWERS. MODERATE OR GOOD, OCCASIONALLY POOR. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
On Dec 23, 2008, at 9:33 AM, Zefram wrote: Suppose that people in the future overwhelmingly want local civil time of day to continue to approximate local solar time of day. Again, the issue is mean solar time, not local solar time. An underlying timescale based on mean solar time is what allows all the local civil/solar issues to be resolved cleanly together. Just to be clear, it also isn't a question of people's "preferences", it is a question of discovering requirements implicit in our society. One may or may not agree with me that mean solar time is the key, but at no point over the millennia will the issue just be one of what people want (whether overwhelmingly or not). [...] I think in this situation it is inevitable that the timezones will shift. [...] After five millenia Britain might be on TI-65h. The local date gets to be substantially different from the TI date, to the same sort of degree that the local hour-of-day currently differs from the UTC hour-of-day. Timezone offsets continue to grow secularly without bound. Sounds unworkable? Possibly, but I can't put my finger on any reason why large offsets per se would cause the system to collapse. Because time is a quantity with memory. Historians looking backward want to relate events worldwide and arrange them into coherent timelines. Whatever the preferences of the ITU, they will discover that it is simply unacceptable to allow local dates to vary secularly from civil timekeeping dates. We can speculate on all sorts of systems of timekeeping, up to and including Star Trek style stardates. Many different systems can be described that are technically workable. Only one - standard time based on mean solar time - has ever been shown to be *practically* workable. Before adopting another - even by so apparently subtle a change as omitting that first leap second in 2019 - a carefully crafted analysis of the consequences and a coherent plan of action should be developed. Red tape? Bah Humbug! It is simple common sense to plan ahead. The issue isn't one of a second here and there - the issue is keeping the definition of the word "day" straight. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
On Fri, 26 Dec 2008, Rob Seaman wrote: > > Whatever the preferences of the ITU, they will discover that it is > simply unacceptable to allow local dates to vary secularly from civil > timekeeping dates. Civil time *is* a form of local time. > Only one - standard time based on mean solar time - has ever been shown > to be *practically* workable. Two: standard time plus daylight saving time is the other (provided DST is applied according to national rules). Tony. -- f.anthony.n.finchhttp://dotat.at/ SHANNON: SOUTHEASTERLY 4 OR 5, INCREASING 6 OR 7 IN SOUTH. MODERATE OR ROUGH. MAINLY FAIR. MODERATE OR GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
Rob Seaman wrote: >Again, the issue is mean solar time, not local solar time. This sentence doesn't make sense to me. You seem to have a different definition of either "mean" or "local" from me. To be clear: the (periodic) difference between apparent and mean solar time does not affect my argument, so I ignored it; likewise, the difference between solar time at one's actual longitude (local solar time) and solar time at a nearby round-numbered longitude (standard time) is small and does not affect the psychology. >it is a question of discovering requirements implicit in our society. Good point. > Historians looking backward >want to relate events worldwide and arrange them into coherent >timelines. Yes, they'll want the Olson database. >Whatever the preferences of the ITU, they will discover >that it is simply unacceptable to allow local dates to vary secularly >from civil timekeeping dates. I don't see how this follows. Given the Olson database they'll be able to apply the offsets correctly. If the date drift per se really is a problem, that would be a reason to argue for the IDL-jumping version of my scenario, rather than the unbounded-timezone-offset version. -zefram ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
I wrote: Historians looking backward want to relate events worldwide and arrange them into coherent timelines. Zefram replied: Yes, they'll want the Olson database. Precisely. For a scheme such as this to have any chance of working, a requirement is that it be tightly coupled to a mechanism like zoneinfo. This is equivalent to Steve Allen's proposal. Whatever the preferences of the ITU, they will discover that it is simply unacceptable to allow local dates to vary secularly from civil timekeeping dates. I don't see how this follows. Given the Olson database they'll be able to apply the offsets correctly. A further requirement is that there needs to be faith in that database and in how it is tied into the fabric (system of systems) of the world. If the date drift per se really is a problem, that would be a reason to argue for the IDL-jumping version of my scenario, rather than the unbounded-timezone-offset version. Words like "jumping" and "unbounded" reflect that the discontinuities represented by leap seconds remain inherent in the system. One way or another, intercalary corrections (of whatever sort) will remain necessary. Since they are necessary, so is a coherent and reliable mechanism for managing them. The devil-may-care ITU proposal is insufficient. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
In message: <20081227134333.gm2...@fysh.org> Zefram writes: : > Historians looking backward : >want to relate events worldwide and arrange them into coherent : >timelines. : : Yes, they'll want the Olson database. How is the Olson database fundamentally different than the historical data that a future historian would have based on the measurements of the delta between what we call today TAI and UT1 times? It is just more data for them to swizzle into their calculations? Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
M. Warner Losh wrote: How is the Olson database fundamentally different than the historical data that a future historian would have based on the measurements of the delta between what we call today TAI and UT1 times? It is just more data for them to swizzle into their calculations? Because a mean solar clock is automatically a stable subdivision of the calendar - stable over long periods of time as well as geographically. Noon on two different days is separated by an integral number of days no matter what period of time separates the two dates and how the length of day may have varied in the interim. There is no swizzling needed if civil timekeeping remains tied to the Sun. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
In message <20081227.192406.1683994734@bsdimp.com>, "M. Warner Losh" writes : >In message: <20081227134333.gm2...@fysh.org> >Zefram writes: >: > Historians looking backward >: >want to relate events worldwide and arrange them into coherent >: >timelines. >: >: Yes, they'll want the Olson database. > >How is the Olson database fundamentally different than the historical >data that a future historian would have based on the measurements of >the delta between what we call today TAI and UT1 times? It is just >more data for them to swizzle into their calculations? In addition to the Olsen database, the book "Calendrical Calculations" is probably required. -- 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] civil-solar correlation with TI
Poul-Henning Kamp wrote: In addition to the Olsen database, the book "Calendrical Calculations" is probably required. Good point. To count days and align international timelines using the current civil timescale, civilians (e.g., historians) need none of this. Under the ITU's plan to degrade UTC, civilians will need to hire experts like us to perform this simple task. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
In message: Rob Seaman writes: : M. Warner Losh wrote: : : > How is the Olson database fundamentally different than the : > historical data that a future historian would have based on the : > measurements of the delta between what we call today TAI and UT1 : > times? It is just more data for them to swizzle into their : > calculations? : : Because a mean solar clock is automatically a stable subdivision of : the calendar - stable over long periods of time as well as : geographically. Noon on two different days is separated by an : integral number of days no matter what period of time separates the : two dates and how the length of day may have varied in the interim. : : There is no swizzling needed if civil timekeeping remains tied to the : Sun. Actually, they do need to do this now for leap seconds. Plus they need it for sub-second accuracy. Also, mean solar time doesn't mean that all days are 1.0d long. In actuality, there's day to day variations in the length of the day. Since civil time is tied to the atomic scales, this means that noon(local time) is almost never going to be an integral number of days apart due to this variation. It will only be an average. So this argument is flawed from that perspective. So if we keep UTC as is, all we're doing is keeping this variation below a second. Do historians really care if this variation is below a second, below a minute or below an hour? No evidence has been presented as to what level historians care about, the number that care, and why an extra little swizzle at the end would be a burdon. Finally, civil time today is atomic based. It is based on the second as defined by the oscillations of the atoms, not as defined by the rotation of the earth. UTC today includes leap seconds to periodically resynchronize the time scale to the earth's rotation, but it is not based on the earth's rotation. We all know a time will come that this won't be possible. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
In message: Rob Seaman writes: : Poul-Henning Kamp wrote: : : > In addition to the Olsen database, the book "Calendrical : > Calculations" is probably required. : : Good point. : : To count days and align international timelines using the current : civil timescale, civilians (e.g., historians) need none of this. : : Under the ITU's plan to degrade UTC, civilians will need to hire : experts like us to perform this simple task. No need to hire experts. A simple table needs no expert assistance. Historians who care, which would likely be a vanishly small minority, can do the extra swizzle. Since the volume of such calculations would be very small, this doesn't seem to be a compelling argument. Especially since time is already based on an atomic time scale. As its rate of ticking continues to diverge from the earth, we will have to abandon such synchronization. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
On Sun, 28 Dec 2008, Poul-Henning Kamp wrote: > > In addition to the Olsen database, the book "Calendrical Calculations" > is probably required. "Calendrical Calculations" isn't a reliable source for historians in the way that the Olson database tries to be. CC is a mechanized description of how calendars are supposed to work, not a record of how they are actually used. This is particularly important for observational calendars such as the Islamic calendar where practice can and does differ from theory. The tz database attempts to record what timezones were actually used in different places at different times. Tony. -- f.anthony.n.finchhttp://dotat.at/ SOUTHEAST ICELAND: SOUTH OR SOUTHWEST 5 OR 6, DECREASING 4 AT TIMES. MODERATE OR ROUGH. OCCASIONAL DRIZZLE. MODERATE OR GOOD, OCCASIONALLY POOR. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] civil-solar correlation with TI
Tony Finch wrote: >"Calendrical Calculations" isn't a reliable source for historians in the >way that the Olson database tries to be. CC is a mechanized description of >how calendars are supposed to work, Actually it doesn't even fully achieve that. The numerical algorithms are correct, as far as I can see, but the descriptions of the underlying theory are often muddled, riddled with errors and critical omissions. (Count how many different quantities go by the name "RD".) Rather importantly for our purposes, CC ignores the existence of timezones (or, for that matter, longitude). >tz database attempts to record what timezones were actually used in >different places at different times. It would be nice to have the analogous database for calendar usage. -zefram ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
