Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
I wrote: Tony Finch wrote: The local atomic clocks on the Moon or Mars will not run at the same rate as a time signal transmitted from the Earth. More due to being at high altitude than due to relative motion, I believe. I've just found this relevant graph on Wikipedia: http://upload.wikimedia.org/wikipedia/commons/9/98/Orbit_times.png -zefram ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
On Mon, 22 Dec 2008, Zefram wrote: http://upload.wikimedia.org/wikipedia/commons/9/98/Orbit_times.png Cool, thanks for that and the interesting details in your other post. Tony. -- f.anthony.n.finch d...@dotat.at http://dotat.at/ WIGHT PORTLAND PLYMOUTH: VARIABLE BACKING SOUTHEAST 3 OR 4, OCCASIONALLY 5 IN PLYMOUTH. SLIGHT OR MODERATE, OCCASIONALLY ROUGH IN PLYMOUTH. DRIZZLE. MODERATE OR GOOD, OCCASIONALLY POOR. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
Rob Seaman scripsit: One supposes the lunar synodic period would be divided into 30 parts. *One* may suppose it, but others have not, such as Manuel Garcia O'Kelly-Davis, an actual (though fictional) resident of Luna, describing the timescale discussions of the Ad-Hoc Congress for Organization of Free Luna: Another time they argued time. Sure, Greenwich time bears no relation to lunar. But why should it when we live underground? Show me loonie who can sleep two weeks and work two weeks; lunars don't fit our metabolism. What was urged was to make a lunar exactly equal to twenty-eight days (instead of 29 days, 12 hours, 44 minutes, 2.78 seconds) and do this by making days longer--and hours, minutes, and seconds, thus making each semi-lunar exactly two weeks. Sure, lunar is necessary for many purposes. Controls when we go up on surface, why we go, and how long we stay. But, aside from throwing us out of gear with our only neighbor, had that wordy vacuum skull thought what this would do to every critical figure in science and engineering? As an electronics man I shuddered. Throw away every book, table, instrument, and start over? I know that some of my ancestors did that in switching from old English units to MKS--but they did it to make things easier. Fourteen inches to a foot and some odd number of feet to a mile. Ounces and pounds. Oh, Bog! Made sense to change that--but why go out of your way to create confusion? The World Series does seem an egregiously stupid name, though. No - they simply ought to extend it to teams from Japan and the Dominican Republic, etc. But that wouldn't be the World Series, it would be another thing by the same name; a thing which arguably should exist, but not meeting the original issue, which can be met only by rectification of the name. -- John Cowan co...@ccil.org http://www.ccil.org/~cowan Statistics don't help a great deal in making important decisions. Most people have more than the average number of feet, but I'm not about to start a company selling shoes in threes. --Ross Gardler ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
On Dec 19, 2008, at 10:34 AM, John Cowan wrote: Rob Seaman scripsit: One supposes the lunar synodic period would be divided into 30 parts. *One* may suppose it, but others have not, such as Manuel Garcia O'Kelly-Davis, an actual (though fictional) resident of Luna, describing the timescale discussions of the Ad-Hoc Congress for Organization of Free Luna: Another time they argued time. Sure, Greenwich time bears no relation to lunar. But why should it when we live underground? Show me loonie who can sleep two weeks and work two weeks; lunars don't fit our metabolism. What was urged was to make a lunar exactly equal to twenty-eight days (instead of 29 days, 12 hours, 44 minutes, 2.78 seconds) and do this by making days longer--and hours, minutes, and seconds, thus making each semi-lunar exactly two weeks. So the two things that would be preserved (in addition to honoring the lunar day/night cycle), are sexagesimal notation and the 7-day week? I wonder if Heinlein even realized his tunnel vision here? At any rate, I'm skeptical that a cycle of 25h19m (in SI units) would be physiologically acceptable even without the next point: Sure, lunar is necessary for many purposes. Controls when we go up on surface, why we go, and how long we stay. But, aside from throwing us out of gear with our only neighbor, had that wordy vacuum skull thought what this would do to every critical figure in science and engineering? As an electronics man I shuddered. Throw away every book, table, instrument, and start over? I know that some of my ancestors did that in switching from old English units to MKS--but they did it to make things easier. Fourteen inches to a foot and some odd number of feet to a mile. Ounces and pounds. Oh, Bog! Made sense to change that--but why go out of your way to create confusion? The underlying alternatives outlined in the 1999 GPS World article (and in my screed http://iraf.noao.edu/~seaman/leap) remain. To synchronize two clocks (Earth and Lunar in this case), you can adjust the rates on one end or the other, or you can reset the zero point of one or the other on some sort of schedule. Additionally, if the differential rates continue to vary, then the scheduling has to vary. If the clock rates are too far apart, the best solution is to put two clocks on the wall. (Most of the arguments over the past five years are equivalent to a requirement to label the clocks correctly. Don't call it UTC if it isn't UTC.) It is only that the SI second (essen) and the civil second (1/86400 of a mean solar day) are still very close that a scheme of ignoring the whole thing for a few generations can even be entertained. If the SI second had been chosen (as it arguably should have been) to be some different, non-denumerable duration, then we would be worrying about civil timekeeping as the entirely separate issue that it is. This idea reaches back to the dawn of precision timekeeping. Harrison's #4 clock succeeded where the first three failed because he stopped trying to build a perfect clock, and instead chose to calibrate imperfect chronometers. His navigational solution would have worked perfectly fine if the rate of the chronometer was quite distinct from the diurnal rate. Similarly, if sexagesimal were reserved for angles (like mean solar time), instead of being misused for interval timing, issues as above would be simplified because Heinlein wouldn't need to fret unnecessarily over scientific and engineering units. My copy of The Moon is a Harsh Mistress is in some box in the garage. I gather the passage is implying that the loonies simply use GMT, rather than lunations (other than that this matters for many purposes) or trying to use the rationalized 28-day units? The key issue in the passage above is the implicit meaning for timekeeping on Earth, not the Moon. (Any good quotes from Clarke or Asimov? Heinlein is always a bit too concerned with his underlying political agenda to focus on details of technology for its own sake.) Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
In message 20081218030954.ga26...@ucolick.org, Steve Allen writes: http://www.ucolick.org/~sla/leapsecs/deltat.html I belive your LORAN-C TOC is wrong, that should be 01-01-1958 00:00:00 UTC -- 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] WP7A status and Re: clinical evidence about time and sun
Poul-Henning Kamp wrote: A timescale which takes earth rotation into account should be called Terrestial Time Coordinated (TTC ?) and the timescale that takes into account the rotation of Mars should be MTC. The name MTC has already been used to refer, not to the Martian equivalent of UTC, but to the Martian equivalent of GMT. Obviously, the people who did this are among those who don't think of the leap seconds in UTC, but instead use UTC as the label for vague UT. They were in fact people at NASA working on the Mars rover missions.[0] I think the fact that professionals in such a closely-related discipline can't keep UT and UTC straight says something about the viability of working with leap seconds. It chimes with how we've seen all manner of technical systems, even including NTP implementations, misbehave around leap seconds. It also matches my experience in editing the Wikipedia articles on time scales: my plan to merge [[leap second]] into [[Coordinated Universal Time]] was overwhelmingly rejected, by people to whom the distinguishing feature of UTC is its Universality, rather than its Coordination. The Martian time scale in question, the local solar time on the Airy meridian, is better described by the older name Airy Mean Time (AMT). We have a pretty good idea of the time on that timescale now, to within a second. (Though we did not have that precision when the rovers landed, which explains the odd offsets of the mission timezones.) Creating a Martian equivalent for UTC is a much more complex job: it requires the concepts of Marticentric Coordinate Time (TCM) and Martian Time (TM), and an atomic time scale Martian Atomic Time (TAM) that realises TM. That'll require actual atomic clocks on Mars. Then MTC would have the job of coordinating TAM with AMT (possibly also to be named MT1). I find that the mental exercise of the previous paragraph drives home just how artificial UTC and TAI are compared to UT1. Pondering MTC also gives some insight into the far future of UTC: current MTC, if we could implement it, with TAM ticking SI seconds, would already require more than one leap second per *minute*. A minute of AMT occupies about 61.65 SI seconds. We'd certainly need some arithmetical scheduling. But the universal timescale should depend on nothing that is not uniform throughout the Universe. A good choice would be an easy to measure and well defined atomic resonance under well defined relativist circumstances. Current physical theory does not identify any preferred reference frame. The closest time scale we have so far is TCB, which is based on a reference frame in which the barycentre of the solar system is at rest. -zefram [0] Michael Allison and Robert Schmunk, Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock, Dec. 13 2005, http://www.giss.nasa.gov/tools/mars24/help/notes.html. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
In message: 18762.53127.165662.23...@gromit.timing.com John Hein jh...@timing.com writes: : Solutions for applications can and should rely on properly designed : systems : : Indeed. And relying on a system whereby you receive six months notice : is one of the problems with the current system of leap seconds. I find this ironic too. We must have a predictable future is fundamentally incompatible with the current system of leap seconds. There's no predictability to the current system at all. There's no way to know how many leap seconds that will elapse between now and the end of 2040. Also, trying to force a system that's been in place for 37 years with known limitations to last 1000's of years seems like an unwise engineering move. When Pope Gregor reformed the calendar, it was based on hundreds if not thousands of years of observations, and was known to be good for tens of thousands of years without anything else ever changing, or any need for any authority to dictate leap days. The necessity to say 'yea or nay' on leap seconds at a given time, as opposed to a mechanical means of knowing, is a fundamental flaw with the current system of leap seconds. I guess the fundamental problem is that eventually, the day will be 86401 seconds. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
On Dec 18, 2008, at 4:27 PM, Zefram wrote: I think the more fundamental issue is that we will, any way round, need data that relates the two flavours of time. A single clock reading can't give both types of time in the absence of such knowledge. ...and wouldn't a description of how these data would be conveyed make a useful section of any planning document related to fundamentally changing the definition of this standard? One might suggest such a section would in other circumstances be required - and be widely understood to be required - in order to adopt a fundamental change like this. Rather, the ITU wants to entirely remove the current DUT1 reporting requirement. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
On Dec 18, 2008, at 9:45 PM, John Cowan wrote: Ah, but will Lunar civil time be mean solar time on Luna? For many purposes, yes. The Apollo missions were planned to occur in daylight, for instance. For other purposes, the factor of ~30 contrast between the lunar day and the innate human diurnal rhythms would result in the natural use of a clock similar or identical to mean solar time on Earth. One supposes the lunar synodic period would be divided into 30 parts. It would be interesting to see whether the Earth day or Lunar day would win out - that is, whether the synodic period would be evenly divided by 30 to set a local clock rate, or whether the Earth day (meaning the mean solar day on Earth, of course) would trump being evenly divisible into the local day. Ignore everything else we've ever discussed. The central issue with several of us is that the meaning of the UTC standard should not be changed. If a decision (ideally a calm, reasoned and publicly transparent decision) is made to relayer civil timekeeping on a clock without leap seconds, then don't call that clock UTC. As you know, I support that. Copacetic. How about calling it - say - GPS? The public already knows GPS, already owns devices that speak it, and already regards it as a brand name denoting high precision/accuracy timekeeping. I think the public associates GPS with location rather than time. As an aside, I highly recommend Steven Pinker's The Stuff of Thought, which persuasively argues that the grammatical structures we use to describe time are precisely the same as those used to describe (and reason about) spatial information. GPS is a very popular brand name that could certainly be used as a component of a successful campaign to market a new concept of civil timekeeping. Redefining UTC, on the other hand, will simply make what is a somewhat obscure standard even more obscure. The World Series does seem an egregiously stupid name, though. No - they simply ought to extend it to teams from Japan and the Dominican Republic, etc. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
On Dec 16, 2008, at 9:07 AM, Poul-Henning Kamp wrote: http://www.navcen.uscg.gov/cgsic/meetings/48thmeeting/Reports/Timing%20Subcommittee/48-LS%2020080916.pdf Thanks for posting this - extremely helpful! On Dec 16, 2008, at 10:47 AM, Poul-Henning Kamp wrote: Please discontinue use of your disconnecting civil time from the sun red herring, it has nothing to do with reality anywhere on Earth, and only serves to confuse. This, however, is an example of an unhelpful statement. You may (or, obviously, may not) agree with statements from others on the list. If not, by all means make a passionate response. But it is not only rude, but counterproductive to try to tell others what they can or cannot say. For instance, I happen to think your notion about perpetually revolving the time zone offsets around the planet under completely local authority is spectacularly unworkable. However, you have my encouragement (and more to the point, don't need it) to keep trying to develop supporting arguments for it. On the other hand, I won't seek to justify the basis of Steve's message because we have done so over and over. When some say civil time they mean the underlying international timescale (UTC or not, but currently everywhere some approximation to GMT). When others say civil time they mean local standard time. One is obviously layered on the other (whatever chaos might be introduced by standards bodies, and whether or not time zone offsets are a function of time), and the particular meaning is almost always clear from the context of a particular message. Rob ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
Rob Seaman scripsit: For instance, I happen to think your notion about perpetually revolving the time zone offsets around the planet under completely local authority is spectacularly unworkable. Why are such changes in timezone unworkable, provided they don't happen too often? The median frequency of changes in timezone (neglecting DST changes) is several per century as it is: see the Olson data. -- And it was said that ever after, if any John Cowan man looked in that Stone, unless he had a co...@ccil.org great strength of will to turn it to other http://ccil.org/~cowan purpose, he saw only two aged hands withering in flame. --The Pyre of Denethor ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] WP7A status and Re: clinical evidence about time and sun
On Wed 2008-12-17T19:23:16 -0700, Rob Seaman hath writ: The historical trend (http://www.ucolick.org/~sla/leapsecs/ancient.png ) won't just vanish with the actions of the ITU, it will pop up again somewhere else. I appreciate the link to the LOD plot, and I have faith in the readership of LEAPSECS, but the sad fact is that the general public cannot do an integral in their heads, so I prefer now to point at http://www.ucolick.org/~sla/leapsecs/deltat.html which shows the full glory of Morrison Stephenson's work in the context of historical events. -- 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
