Re: the tail wags the dog
On Jan 24, 2006, at 12:50 AM, Peter Bunclark wrote: I don't think Rob meant the above to be a complete course on navigation! ...although as a fan of Patrick O'Brian I am qualified not only to teach navigation, but also the violin and Catalan. You should see me in a Bear costume. Good example of a timekeeping decision made by a (very tiny) minority over the majority. The issue here is the meaning of the preposition over. It is not unusual for we anointed of Hephaestus (the god of dweebs) to be placed in the position of making decisions for others - who may not even be aware an important issue is being considered. The more fundamental question is whether the requirements of the majority are properly considered and given appropriate weight. How nice indeed, it would be, if the months were fixed to match lunations. Quadratic despair still lurks, of course, since the month is lengthening for exactly the same reason as the day. Well, despair would be lurking if we tried to match the length of the month (a natural phenomenon) to an SI unit (such as the second). Rob
Re: the tail wags the dog
In message [EMAIL PROTECTED], Rob Seaman writes: Quadratic despair still lurks, of course, since the month is lengthening for exactly the same reason as the day. Well, despair would be lurking if we tried to match the length of the month (a natural phenomenon) to an SI unit (such as the second). You mean the kind of despair where every so often we would have to put our finger on the scales to make them balance ? Ie: Just like when we match the length of the day/year to the SI second ? I think the crucial insight here is that geophysics makes (comparatively) lousy clocks and we should stop using rotating bodies of geophysics for timekeeping. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
Re: the tail wags the dog
On Jan 24, 2006, at 8:06 AM, Ed Davies wrote: James Maynard wrote: The problem is not that the SI second is not based on a natural phenonemon (it is), but that the periods of the various natural phenonema (rotations of the earth about its axis revolutions of the earth about the sun, revolutions of the moon around the earth, etc.) are both incommensurate and changing. Not to mention the hyperfine wibbles of caesium-133. ...and we wonder why our less technically oriented loved ones tune out when we start to speak :-) Point taken - these are all natural phenomena. But then, so are all the other issues we've ever raised. The rotation of the Earth and the revolutions of its Moon are natural phenomena we have little ability (and less reason) to attempt to control. Hyperfine wibbles are things that humans can hope to tame in various ways. No one disputes that our clocks have been improved wondrously - but the point of a good clock is the point of other technology, to tame nature in the service of mankind. (Taming mankind in the service of nature? Hmm - there's a thought.) The question on the table is whether mankind is better served by gracefully accommodating the charming quirks of Earth and Moon - or whether we should attempt to impose a metric standard, inappropriate to the purpose. Rob
Re: the tail wags the dog
On Jan 24, 2006, at 7:21 AM, Poul-Henning Kamp wrote:I think the crucial insight here is that geophysics makes (comparatively) lousy clocksThe crucial insight is that the Earth is not a clock at all, but rather the thing being timed.and we should stop using rotating bodies of geophysics for timekeeping.We already have. The question is whether everybody on the planet needs to adjust their clocks to match requirements imposed by the high precision timekeeping needs of projects that already have options other than UTC.The follow-up question is whether attempting to ignore an inevitable outcome is better than simply dealing with it through the intervening centuries. All proposals (other than rubber seconds or rubber days) face the same quadratically accelerating divergence between clock and Earth.Rob
Re: the tail wags the dog
Rob Seaman wrote: All proposals (other than rubber seconds or rubber days) face the same quadratically accelerating divergence between clock and Earth. By rubber seconds you, presumably, mean non-SI seconds. What do you mean by rubber days? I'd guess you mean days which are divided into SI seconds but not necessarily 86 400 of them. Just to be clear, is that right? Ed.
Re: the tail wags the dog
Steve Allen said: The official time of the US for commerce and legal purposes is UTC(NIST). The official time of the US DOD is UTC(USNO). The official time of the Federal Republic of Germany is UTC(PTB). etc. The official time of the UK is GMT. -- Clive D.W. Feather | Work: [EMAIL PROTECTED] | Tel:+44 20 8495 6138 Internet Expert | Home: [EMAIL PROTECTED] | Fax:+44 870 051 9937 Demon Internet | WWW: http://www.davros.org | Mobile: +44 7973 377646 Thus plc||
Re: the tail wags the dog
On Mon 2006-01-23T14:02:01 +, Clive D.W. Feather hath writ: Steve Allen said: The official time of the US for commerce and legal purposes is UTC(NIST). The official time of the US DOD is UTC(USNO). The official time of the UK is GMT. Please distinguish between official and legal. The legal time of the US is (in many more words) GMT. The officials who are charged by congress with the task of providing time provide UTC. The situation is exactly the same in the UK. http://www.npl.co.uk/time/truetime.html http://www.npl.co.uk/time/msf.html I reiterate that the tail wags the dog. -- Steve Allen [EMAIL PROTECTED]WGS-84 (GPS) UCO/Lick ObservatoryNatural Sciences II, Room 165Lat +36.99858 University of CaliforniaVoice: +1 831 459 3046 Lng -122.06014 Santa Cruz, CA 95064http://www.ucolick.org/~sla/ Hgt +250 m
Re: the tail wags the dog
In message: [EMAIL PROTECTED] Steve Allen [EMAIL PROTECTED] writes: : The legal time of the US is (in many more words) GMT. : The officials who are charged by congress with the task of providing : time provide UTC. The legal time in the US is the mean solar time at a given meridian, as determined by the secretary of commerce (the actual law is a little more verbose than this, but this is an accurate boil down) plus some weird options for 'border states' which timezone they are in. This is why NIST provides UTC and leap seconds happen on the UTC schedule rather than some other schedule that would produce the same results. It is also why there are leap seconds and not the old-style frequency adjustments + tiny steps. Both of these schemes fit the law, as it is rather vague in the words it uses in a legal sense (the term mean solar time isn't legally defined, but does have an accepted scientific meaning). Other schemes could also fit the law that aren't UTC today since there's no what we would call 'DUT1 tolerance' written into the law... Warner
Re: the tail wags the dog
Rob Seaman scripsit: The legal time in the US is the mean solar time at a given meridian, as determined by the secretary of commerce ...and many may have seen Mr. Gutierrez shooting the sun with his sextant out on the Mall in front of the AS Museum :-) With all the words that have flowed over the spillway, I'm not sure the point has been made that a feature of solar time is precisely that it can be reliably recovered from observations whenever and wherever needed (once you are located with respect to a meridian, of course). I don't understand this. You can't shoot the mean sun with a sextant, only the friendly (apparent, whatever) sun. So at the very least you need an analemma. In any case, the majority of the world has managed to live with the fact that the day-of-month can no longer be recovered by examining the moon, although if we were still hunter-gatherers a purely lunar calendar would make a lot of sense. -- XQuery Blueberry DOMJohn Cowan Entity parser dot-com [EMAIL PROTECTED] Abstract schemata http://www.reutershealth.com XPointer errata http://www.ccil.org/~cowan Infoset Unicode BOM --Richard Tobin
Re: the tail wags the dog
Steve Allen [EMAIL PROTECTED] wrote: The CGPM recommendation on the timescale everyone should use says UTC. UTC(insert your national time service here) is available in real time. TAI is the mathematical (really the political or diplomatic) entity upon which UTC is ostensibly based, but the practical and legal reality is the other way around. Has it occurred to any of you that *THIS* is the very root of the problem, that *THIS* is what we need to change? Also, isn't TAI readily available in real time from GPS? (How difficult can it be for the routine parsing the data stream from the GPS receiver to add 19?) OK, OK, it'll be TAI(GPS) rather than true TAI, but then your UTC is really UTC(NIST) or UTC(USNO) or UTC(PTB) or whatever rather than true UTC. MS
Re: the tail wags the dog
Michael Sokolov wrote: Steve Allen [EMAIL PROTECTED] wrote: TAI is the mathematical (really the political or diplomatic) entity upon which UTC is ostensibly based, but the practical and legal reality is the other way around. Has it occurred to any of you that *THIS* is the very root of the problem, that *THIS* is what we need to change? Frankly, I didn't understand Steve's remark at all. Practical reality is that most national standards laboratories use precise frequency standards to maintain a count of SI seconds as a rendition of TAI. When it comes to establishing and distributing UTC or legal time, they consult the publications of the IERS and/or local law, and do some simple math. Legal reality (I speak for The Netherlands) is also not the other way around but appears to ignores TAI and the leap second issue completely. Legal time is equated to CET (or CEST) which is considered sufficiently well-known to leave it at that. In practice, the VSL laboratory of the NMI in Delft, which is supposed to provide legal time, works as described above. I can imagine other countries are not much different. So from a legal standpoint, there is no problem. Countries will happily folow any standard the scientific community comes up with, finds general use, and is halfway usable. Like they did with UTC without caring a *** where it actually comes from. Nero Imhard Oegstgeest, The Netherlands
Re: the tail wags the dog
In message: [EMAIL PROTECTED] [EMAIL PROTECTED] (Michael Sokolov) writes: : Steve Allen [EMAIL PROTECTED] wrote: : : The CGPM recommendation on the timescale everyone should use says UTC. : : UTC(insert your national time service here) is available in real time. : : TAI is the mathematical (really the political or diplomatic) entity : upon which UTC is ostensibly based, but the practical and legal : reality is the other way around. : : Has it occurred to any of you that *THIS* is the very root of the problem, : that *THIS* is what we need to change? I believe so. : Also, isn't TAI readily available in real time from GPS? (How difficult : can it be for the routine parsing the data stream from the GPS receiver : to add 19?) OK, OK, it'll be TAI(GPS) rather than true TAI, but then : your UTC is really UTC(NIST) or UTC(USNO) or UTC(PTB) or whatever rather : than true UTC. You can get an excellent approximation of TAI from GPS, assuming that you use a sane receiver... Some firmware doesn't deal well with reporting the raw, uncorrected GPS time, but many do it well. Depending on your needs, you may have to put the GPS receiver into a mode that only reports URC... Well, you get the idea. It can be done to a degree of accuracy that most people will accept, but the post-processed time scale calculations are a little better than what happens in real time. Warner
