Re: [LEAPSECS] Cheating means more planning, not less
My apologies for the long reply. The personal attacks reached a tipping point. Others should feel free to skip this (as I'm sure they do all my messages :-) Poul-Henning Kamp wrote: Rob Seaman writes: Just one comment. The requirements for timing applications (of whatever precision) are distinct from the requirements for civil clock applications. You seem to think civil clock applications is little old ladies walking to church once a week. My parenthetical remark about precision seems to have been insufficient disclaimer. Apologies for yet another Strother Martin moment. That is one use case, yes. But the real point I'm failing to communicate is simply the distinction between clocks and timers. Since it is a truism that every thread on leapsecs has been discussed previously, you can find some insightful comments from folks like Steve Allen in the archives on this topic. The two different types of timekeepers may previously have been referred to as clocks and chronometers. A timer keeps interval time - highly precise, but perhaps only accurate in a relative sense. A clock keeps Earth orientation time (or other fundamental reference) - accurate in an absolute sense, but not necessarily very precise. The point is system engineering again. The requirements for an interval timer are simply distinct from the requirements for a clock. They may overlap, they may not. One or the other set of requirements may be more important for a particular application. As all within reach of my keyboard surely know, I believe civil timekeeping to be fundamentally dependent on requirements pertaining to Earth orientation. I am well aware that others here (where here is a place to be understood metaphorically, see Steven Pinker), believe that interval timekeeping requirements are more critical, at least since the invention of the computer. In the statement above I was trying to separate the two in a noncontroversial way. Apparently I failed. Let's see. Is the distinction clearer if I say that an egg timer and the clock drive of a telescope have different requirements? Anyway, to resolve the requirements for such divergent applications, I have been recommending that well-known system engineering techniques be followed. Techniques that are eminently applicable to situations in which diverse entrenched positions have been taken. On the other hand, Warner, for instance, has simply suggested that one or another party steel themselves to lose. If we assume somebody has to lose, then perhaps that will become a self-fulfilling prophesy. I don't assume anybody has to lose. In any event, UTC has always provided access to interval time much more precisely (milliseconds or better via radio signals, microseconds or better via NTP) than to Earth orientation time (0.9s uncorrected, 0.1s corrected). At any point have I suggested that interval time should be degraded? Rather, the ITU is unilaterally proposing to dramatically degrade access to the Earth orientation related features of clocks worldwide. As I believe you should know by now, I don't appreciate this and have been trying to argue against it. For some reason, this appears to upset you. For some reason, the subject of the discussion keeps being changed. Leap seconds are simply a facet of an engineering solution. A different solution could involve other engineering choices. The ITU is not pursuing a different solution, they have been relentlessly pursuing the destruction of the current solution. I believe they have taken this path because they have skipped important steps of standard system engineering methodology. Central to this is a rush to judgement, the familiar human quality of failing to explore the problem space sufficiently before seizing on a specific solution. Perhaps there is an evolutionary argument for this human behavior - something about fleeing lions on the savannah. How do you say look before you leap in Danish? Each problem has many solutions. If we didn't have to keep fending off the ITU's deliberations, we could flesh out some high priority use cases (on all sides), utilize these to discover the underlying requirements shared by those use cases, and dispassionately consider alternative solutions that have the likelihood of making everybody happier with the ultimate consensus. This is not only a better decision pathway, it is most assuredly a pathway that will be traversed much quicker than the nine years that the ITU has squandered. A modern passengerplane moves approximately 300 meters per second. Are you willing to to accept a +/- 300 meter tolerance on the radar track during final approach in Cat3 conditions, if you are on the plane ? How much havoc do you think a one second difference makes in a modern robotic car-production facility ? Have you ever wondered why the car
Re: [LEAPSECS] Cheating means more planning, not less
I think IERS Bulletin A might represent the current state of the art for predicting Earth orientation. It is produced by USNO. Latest bulletin is here: http://www.iers.org/products/6/11769/orig/bulletina-xxi-052.txt. It provides a table of UT1-UTC values to the end of 2009. It also provides an estimated function and its standard deviation that can be used to extend the table. How accurate are the predictions (especially the long-term ones) really? One would have to compare one of the historical empirical functions with actual UT1 data. Not sure if anyone has done that recently. Perhaps Demetrios knows? -- Richard Langley P.S. For those wanting to refresh their memories on the details of the history of the leap-second business, have a look at http://tycho.usno.navy.mil/leapsec.html. Quoting Rob Seaman sea...@noao.edu: What exactly is the current state of the art for predicting Earth orientation? It is a shame that there are no lurkers here who could answer that question. === Richard B. LangleyE-mail: l...@unb.ca Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ === ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
In message: 20081229165202.gp2...@fysh.org Zefram zef...@fysh.org writes: : Richard B. Langley wrote: : How accurate : are the predictions (especially the long-term ones) really? : One would have to compare : one of the historical empirical functions with actual UT1 data. : : We discussed this in 2007-01 in a thread titled UT1 confidence. : No firm answers were forthcoming regarding present IERS capability. : : PHK noted that the accuracy estimation formula in Bulletin A gives : unbelievable results if applied to periods of decades. We don't know : how far out that formula, or the DUT1 estimation formula, are intended : to be applied. Yes. I think he said that they worked well out about 10 years, but that we should graph the actual vs historical predictions to make sure... : Steve Allen pointed at some interesting papers, of which the most relevant : was http://www.ucolick.org/~sla/leapsecs/torino/arias_3.pdf. This paper : looks at (retrospectively) predicting UT1-TAI two and three years ahead, : and how well those predictions match reality. These predictions were : made with a fairly naive algorithm, which in the short term performs : much more poorly than what IERS does. The three year predictions were : all correct to within 1.0 s. I'd note that Bullitin A data is available, and one could graph the performance of different time lines vs actual over a period of the last few years. I was thinking of doing this data crunching myself, but time has gotten away from me... Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
In message 3326254a-dd7a-40e6-a014-3958344aa...@noao.edu, Rob Seaman writes: My apologies for the long reply. No apologies for the short reply. http://redwing.hutman.net/~mreed/warriorshtm/ferouscranus.htm 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] Cheating means more planning, not less
In message 20081227.192200.-1749704408@bsdimp.com, M. Warner Losh write s: : The ITU has a responsibility to consider options with a long term : future. ITU has no such responsibility: 1 The purposes of the Union are: a) to maintain and extend international cooperation among all its Member States for the improvement and rational use of telecommunications of all kinds; [...] (http://www.itu.int/net/about/basic-texts/constitution/chapteri.aspx) If leap-seconds impeede telecommunications, ITU has a responsibility to get rid of them. -- 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] Cheating means more planning, not less
I wrote: The ITU has a responsibility to consider options with a long term future. Poul-Henning Kamp writes: ITU has no such responsibility: 1 The purposes of the Union are: a) to maintain and extend international cooperation among all its Member States for the improvement and rational use of telecommunications of all kinds; [...] (http://www.itu.int/net/about/basic-texts/constitution/chapteri.aspx) If leap-seconds impeede telecommunications, ITU has a responsibility to get rid of them. 1) An organization with a limited scope (telecommunications) should not control a standard with a much broader scope (timekeeping). 2) All organizations have an implicit responsibility not to pursue shortsighted agendas. If an option has no long term future, the ITU certainly has no business considering it. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
In message bf590d36-97c8-49fe-a6e3-1e4634c5b...@noao.edu, Rob Seaman writes: A global village implies global citizens. People have complex needs that place more stringent timekeeping requirements of all sorts now than 50 years ago. Rob, you keep making these claims that a lot of 'needs' and 'requirements' are being overlooked. Why is it that you never offer a single concrete example ? The ITU proposal is simply a bad proposal. Improve the proposal. Seek consensus before voting on the next one. I think it is a pretty good proposal and I hope nobody get killed by leap seconds before it takes effect. 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] Cheating means more planning, not less
In message: 0b4062cc-0e7e-407f-a856-37f9c74dc...@noao.edu Rob Seaman sea...@noao.edu writes: : I wrote: : : The ITU has a responsibility to consider options with a long term : future. : : Poul-Henning Kamp writes: : : ITU has no such responsibility: : : 1 The purposes of the Union are: : : a) to maintain and extend international cooperation : among all its Member States for the improvement and : rational use of telecommunications of all kinds; : : [...] : : (http://www.itu.int/net/about/basic-texts/constitution/chapteri.aspx) : : If leap-seconds impeede telecommunications, ITU has a responsibility : to get rid of them. : : : 1) An organization with a limited scope (telecommunications) should : not control a standard with a much broader scope (timekeeping). : : 2) All organizations have an implicit responsibility not to pursue : shortsighted agendas. If an option has no long term future, the ITU : certainly has no business considering it. Leap seconds was a short-sighted agenda. The goal was noble, but the implementation was flawed. Changing things to be less flawed is better. But in any such change there will be winners and losers. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
On Sat, 27 Dec 2008, M. Warner Losh wrote: However, the die was cast on this in 1958 when the second was defined in terms of atomic behavior. At that point, the game was up, since the basic unit of time was decoupled from the day. The decoupling occurred before then, when the second was defined in terms of the length of the tropical year established by Newcomb. The atomic second was calibrated to match this older definition. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ FISHER GERMAN BIGHT: EAST OR SOUTHEAST 4 OR 5, OCCASIONALLY 6 IN GERMAN BIGHT. SLIGHT OR MODERATE. FAIR. GOOD. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
On Sun, 28 Dec 2008, David Malone wrote: Broad agreement and consensus is the foundation of civil time. The way that leap seconds work clearly does not have enough consensus, in that people still produce software and standards and specifications that are incompatible with leap seconds. This is not a particularly good metric. A lot of people (and systems) are incompatible with the Gregorian calendar and make every fourth year a leap year. Similarly, an amount of software was incompatible with the twenty first century, but we went ahead with that anyway ;-) I don't think hese are good counter-examples. The Y2K1 bug is beyond the design lifetime of a lot of systems - in fact the next big breakage is much sooner, in 2036, and there's still not much sign of work to fix it. Short design lifetimes were also a major reason for the Y2K bug, and in that case everyone agreed that it was a bug and agreed to fix or retire the broken software. However not everyone agrees that being incompatible with leap seconds is a bug, and they often deliberately design systems fully aware that they are incompatible. That is, design teams and standards committees repeatedly reach a consensus to ignore leap seconds. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ THAMES DOVER: EAST 5 OR 6, DECREASING 3 OR 4. SMOOTH OR SLIGHT, OCCASIONALLY MODERATE AT FIRST. FAIR. GOOD, OCCASIONALLY MODERATE LATER. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
In message: 0812282316.aa15...@ivan.harhan.org msoko...@ivan.harhan.org (Michael Sokolov) writes: : Rob Seaman sea...@noao.edu wrote: : : However, nobody has been arguing for rubber seconds. : : I have consistently been arguing for rubber seconds! Just like rubber bullets, they are less lethal than real seconds :) Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
In message: 0812290002.aa16...@ivan.harhan.org msoko...@ivan.harhan.org (Michael Sokolov) writes: : M. Warner Losh i...@bsdimp.com wrote: : : I know that nobody is proposing rubber seconds today. : : Wrong! I am! I don't think that's a viable thing to do. It would play havoc with anything except the most low-precision timing applications. And if you don't solve the problem for high-precision timing applications, I'm not sure that it is a viable solution. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
In message: 0812290017.aa16...@ivan.harhan.org msoko...@ivan.harhan.org (Michael Sokolov) writes: : M. Warner Losh i...@bsdimp.com wrote: : : I don't think that's a viable thing to do. It would play havoc with : anything except the most low-precision timing applications. : : But civil time *is* a low-precision timing application! Not really. It is used for timing transactions on exchange boards to the millisecond to ensure proper pricing in fast changing markets... : And if : you don't solve the problem for high-precision timing applications, : I'm not sure that it is a viable solution. : : Those need to use a diffirent time scale decoupled from civil time, : i.e., TAI, GPS, TT, whatever. There need to be two different seconds, : a civil second and a scientific second. The latter would be better : renamed to essen. Right. Good luck with that one... Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
M. Warner Losh wrote: Michael Sokolov writes : M. Warner Losh i...@bsdimp.com wrote: : : I know that nobody is proposing rubber seconds today. : : Wrong! I am! I don't think that's a viable thing to do. It would play havoc with anything except the most low-precision timing applications. And if you don't solve the problem for high-precision timing applications, I'm not sure that it is a viable solution. I figured I'd grab a chance to agree wholeheartedly with Warner :-) Just one comment. The requirements for timing applications (of whatever precision) are distinct from the requirements for civil clock applications. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
Michael Sokolov wrote: But civil time *is* a low-precision timing application! Civil time is not a timing application. It is not an application at all. Whatever the past or future of civil timescales, these form infrastructure that applications are built upon. Precision is one of many requirements incumbent on applications. How the necessary level of precision is obtained may drive choice of one or another or several different timekeeping technologies and standards. M. Warner Losh wrote: And if you don't solve the problem for high-precision timing applications, I'm not sure that it is a viable solution. Those need to use a diffirent time scale decoupled from civil time, i.e., TAI, GPS, TT, whatever. This is often true now, and will often be true in the future. Requirements driving this will tend to split into clock requirements versus interval timing requirements. (Search the archive for chronometer to track down our previous discussions on similar topics.) There need to be two different seconds, a civil second and a scientific second. The latter would be better renamed to essen. Well, as Warner might say, that boat has sailed. We would certainly have more clarity of understanding if the SI second had been called something else, and especially if it had been chosen to have no relation to 1/86,400 of the length of the solar day. Maybe we can just call it Celsius time and make a Celsius second equal to 9/5 of a civil second (as of 1820). Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
In message: 05ed4e1c-dc79-4f30-bd03-69a48940d...@noao.edu Rob Seaman sea...@noao.edu writes: : Maybe we can just call it Celsius time and make a Celsius second : equal to 9/5 of a civil second (as of 1820). hahahhahaha... Of course, the unit of time would have to be the Newcomb.. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
Poul-Henning Kamp wrote: Rob Seaman writes: Focus on the SI second and we see the world through atomic eyeballs. Focus on the primacy of the definition of the day in civil timekeeping, and Earth orientation pops out. Both timescales are necessary. It is well documented that the SI second based timescale has precision and stability requirements on the order of microseconds for telecoms and 10 orders of magnitude smaller for scientific tasks. So I guess we're agreed that this is one of the necessary timescales. Good thing it is already widely available in GPS. (The 10^-16 is a bit extreme :-) A lot of good science happens at a precision less than a second, for that matter. In contrast to this, nobody, including you, seem to be willing to even hazard a guess what level of presision is required or sufficient for the earth orientation clock. The current UTC standard is precise to 0.1 SI seconds. I will hazard a guess that this is sufficient. I believe we both have long since expressed the opinion that this could be relaxed a bit. If the ITU proposal didn't explicitly deprecate DUT1, a new-and-improved UTC could even improve the precision for corrected values while loosening the fit for uncorrected values. The current UTC definition says better than one second, Well, 0.9s. but relative to an abstract definition of earth rotation angle which only astronomers can figure out. I'll spare everybody my familiar harangue on the mean solar day just corresponding to the sidereal day plus a little bit extra to correct for the Earth lapping the Sun once a year. Oh! I guess I won't. Raise your hand if you can't figure out what I just said. Emperical evidence show that most of the earths human population is perfectly happy with local time that is within a couple of hours of proper earth rotation time. And I really will spare folks my other screed on civil timekeeping having nothing to do with local apparent solar time. Since everybody seems to agree on this point, I'm not sure why it keeps coming up. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
On Sat, 27 Dec 2008, Rob Seaman wrote: Rather, a clock can be deposited at any meridian on any planet, set to any time, running at any rate. The question is whether a particular choice of parameters is useful and sustainable. Really what it boils down to is a question of how frequently and by how much we reset our clocks so that civil time (the time used for every-day purposes) has a useful relation to Earth orientation. Additionally if a planet has populations scattered at wide longitudes, the more basic requirement is to organize a coherent system to manage the whole. That's just a matter of quantizing timezone offsets with a reasonably large granularity, as was established in the 19th century. 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 DST is a trivial gimmick layered on standard time. Standard time is a global system layered on the mean solar day. I don't think DST is trivial, nor is it a gimmick. It's very tempting to dismiss DST as a stupidity, especially if you try to understand it without regard to the sociology of time. (I used to think so myself.) There is a very good reason for DST and it is entirely to do with the way people collectively relate to clocks. The most obvious artefacts of this relationship are timetables. Ben Franklin's article was satire, but like all good satire it was pointing out an important failure of civic life: that we are too strictly governed by clocks, regardless of how well we use natural daylight. Back when Franklin was writing, relatively few people lived in cities, and timetables were rare - even ideas like opening hours or working hours. But urban living naturally generates timetables: the timing of deliveries of goods from the counryside determines the opening times of the markets, which determines shopping hours, etc. There is an inevitable coupling of the timing of activities between different walks of life. This became painfully obvious in the USA when (over a period of decades) various jurisdictions disagreed about when and where DST should be applied. The worst chaos occurred when physically overlapping jurisdictions used different rules, so different offices in the same city (e.g. government vs. private) would be operating on different time. The chaos only subsided when the US federal government set rules for how DST should be applied, thereby establishing a consensus. What DST teaches us is that the the most important property that civil time must have is consensus over large areas, whether or not this makes sense w.r.t. natural philosophy. DST is a violation of the concept of standard time, but it is more useful to society than strict adherence to a fixed offset from mean solar time. In fact the same lesson is taught by the establishment of GMT as legal time across Britain. Legal precedent said GMT is a violation of local time - despite the fact that nobody in practice behaved as the law said they should, between the establishment of railway time and the endorsement of GMT as legal time. So how is this relevant to leap seconds? Firstly: The history shows that almost any violence can be done to civil time so long as everyone agrees to it. DST shows that sociology can trump astronomy. (Standard time shows the same thing, but DST's arbitrariness makes this fact much more starkly clear.) Broad agreement and consensus is the foundation of civil time. The way that leap seconds work clearly does not have enough consensus, in that people still produce software and standards and specifications that are incompatible with leap seconds. That fact is probably enough to doom them, just like Britain's local time law was doomed to lose to GMT in the 19th century. Secondly: The commonality between DST and UTC is that both of them require us to reset our clocks occasionally to keep them in a convenient relation to the position of the Earth. DST's resets exist because the way we coordinate our activities using timetables (aligned to mean solar time) doesn't work well with the hours of daylight. UTC's resets exist to keep our clocks matched to mean solar time. Can we not accomplish both goals with the same occasional resets, instead of having two independent reset schedules? Would this also solve the problem of leap seconds disagreeing with the practical consensus model of time? Is there any other way of cleaning up this mess? My sunrise time suggestion is not entirely a joke. Originally its serious purpose was to point out that there is a rational basis for DST: our timetables work better if they are anchored to sunrise than to midday. The point of my recent post is that if you are resetting clocks frequently to make gross adjustments, then you do not also need a second reset schedule to make fine adjustments. Sunrise time has layers of satire and absurdity, as well as of astronomy and sociology, but to explain them all
Re: [LEAPSECS] Cheating means more planning, not less
In message: 5de48b7a-0d30-4580-b110-7687a75a2...@noao.edu Rob Seaman sea...@noao.edu writes: : Identifying the length of the civil day with the length of the mean : solar day is the key to providing that coherence. (True now on Mars : as well as Earth.) The mean solar day is just the sidereal day plus : the synodic correction for lapping the sun once a year. The mean : solar day is a global phenomenon. The eccentricity of the Earth's : orbit and the tilt of its axis (etc) add periodic terms that average : out. Latitude and politics overlay local variations that are a : distraction from the central issue. Tidal slowing, on the other hand, : represents a global long term secular trend. A trend with global : implications demands a global solution. Correct. However, the die was cast on this in 1958 when the second was defined in terms of atomic behavior. At that point, the game was up, since the basic unit of time was decoupled from the day. We transitioned from having rubber seconds, to having rubber days. I suppose we could push this back further when the second was defined in terms of the mean solar day in 1900, since that changed a division of a day, to the day being so many seconds. A subtle difference that appears to have been lost on the people taking this first step, at least at the time. : The trend just happens to be slow enough to permit cheating. : Consensus based planning is necessary *especially* if we decide to : cheat. Cheating is ultimately fruitless over the long term, no matter : what. Yes. First, people cheated with rubber seconds (and why not, since that's how people cheated before the fixing of the length of the second based on atomic behavior: seconds were always rubber since they were defined in terms of a day that varied in length). Doing this similar cheating with atomic clocks presented many operational problems... Second, people cheated with leap seconds. This cheat has presented many operational problems. : The ITU has a responsibility to consider options with a long term : future. A permanent embargo on leap seconds does not have one. : Whatever action the ITU takes, it should be fully and carefully : planned and not obligate our descendants to clean up an embarrassing : mess. This is both true and false. Assuming, for the sake of argument, that we take the position that the ITU has to have a permanent solution to the clock skew problem, that cannot involve leap seconds. In time, they will be needed more than twice a year, then more than 12x a year, and finally, more than once a day. UTC, as defined today, dies once the length of day is 86401 seconds[*]. With these long-term problems on the horizon, I agree that some solution is needed. A leap second embargo is one radical idea don't sync the clocks: publish the delta. The psychological aspects of this are nice, since time won't drift more than a few minutes in anybody's lifetime for several dozen generations yet. This is as long term as other 'permanent' solutions the ITU has promulgated. So I'm not sure I understand this criticism. : 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 : : DST is a trivial gimmick layered on standard time. Standard time is a : global system layered on the mean solar day. But UTC isn't layered on top of the mean solar day. It is merely synchronized to the mean solar day. It is based on the atomic second. And many legal times are being transitioned to UTC. There is a subtle difference between your statement and mine, but an important one. : Ideally we will come out of this exercise with an improvement to : standard timekeeping. Wouldn't it be more fun to pursue that project : rather than playing an endless game of whack-a-mole with ITU politics? Warner [*] Well, it would fail when the day was ~86400.033s since that's when we'd cross the once a month threshold for when the leap seconds can happen. When it crosses 86401, though, we're no longer able to use the same notation we're using today with 23:59:60 although I suppose it could be extended to any hour, then any minute, etc. At some point it becomes totally unworkable, and I arbitrarily selected once a day although my hunch is that it is somewhat before then. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] Cheating means more planning, not less
On Sat 2008-12-27T19:22:00 -0700, M. Warner Losh hath writ: Correct. However, the die was cast on this in 1958 when the second was defined in terms of atomic behavior. At that point, the game was up, since the basic unit of time was decoupled from the day. We transitioned from having rubber seconds, to having rubber days. I suppose we could push this back further when the second was defined in terms of the mean solar day in 1900, since that changed a division of a day, to the day being so many seconds. A subtle difference that appears to have been lost on the people taking this first step, at least at the time. The cesium chronometer was created in the UK 1955, and within only a few months Markowitz of the USNO was rushing to start comparing it with the lunar observations of the dual rate moon camera, and the results of that intercomparison were reported before the experiment was really over. Markowitz in his role as chair of IAU 31 was in a tremendous race to see that the cesium would be calibrated with ephemeris time. There was barely enough time to reduce the observations they had made let alone to comprehend their meaning for either the short term or long term. During that experiment they noted that the rate of earth rotation was in a particularly fast phase of variation. I believe there is a memoir by Markowitz where he indicated the pressure he felt he was under to get an astronomically based definition before the physicists simply chose a number. I haven't yet seen it, and I can't cite it off the top of my head. I have seen no references which indicate that anyone had then recognized that ephemeris time was roughly in agreement with the mean solar day of 1820. There are a number of places where astronomers incorrectly stated that ephemeris time matched the mean solar day of 1900. -- 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
