Leapsecs Listserve Moving
Dear Leap-seconders, For the past seven years, this listserve has served as a forum for a considerable amount of discussion on UTC, generating some heat but more light. I have enjoyed my mostly-silent role as listserve manager, particularly as most of the real work was done by David Johns (and Ken Senior before him). Lately, various technical developments are making it increasingly difficult for the U.S. Naval Observatory to maintain this listserve. We are fortunate that Tom Van Baak has agreed to assume the responsibility of hosting it. You should start submitting your emails to [EMAIL PROTECTED] All current subscribers are automatically being transferred to the new list so the hosting change should be somewhat transparent. Subscription information, archives, and other list information is at: http://six.pairlist.net/mailman/listinfo/leapsecs. We will verify that the new list is working and then on Friday we will close down the old list at rom.usno.navy.mil. If you did not get this message, or do not shortly receive the welcome message on the new list, please let Tom and me know. Tom's email is [EMAIL PROTECTED] and mine is [EMAIL PROTECTED] I will remain a member of this list, and look forward to following the continued discussion. Demetrios Matsakis
Re: Introduction of long term scheduling
As many have pointed out on this forum, these various timescales do have very specific meanings which often fade at levels coarser than a few nanoseconds (modulo 1 second), and which at times are misapplied at the 1-second and higher level. GPS Time is technically an implicit ensemble mean. You can say it exists inside the Kalman Filter at the GPS Master Control Station as a linear combination of corrected clock states. But there is no need for the control computer to actually compute it as a specific number, and that's why it is implicit. Every GPS clock is a realization of GPS Time once the receiver applies the broadcast corrections. GPS Time is steered to UTC(USNO), and generally stays within a few nanoseconds of it, modulo 1 second. UTC(USNO) approximates UTC, and so it goes. The most beautiful reference to GPS Time is The Theory of the GPS Composite Clock by Brown, in the Proceedings of the Institute of Navigation's 1991 ION-GPS meeting. But others, including me, routinely publish plots of it. --Original Message- From: Leap Seconds Issues [mailto:[EMAIL PROTECTED] On Behalf Of Ashley Yakeley Sent: Tuesday, January 09, 2007 2:22 AM To: LEAPSECS@ROM.USNO.NAVY.MIL Subject: Re: [LEAPSECS] Introduction of long term scheduling On Jan 8, 2007, at 22:57, Steve Allen wrote: GPS is not (TAI - 19) What is GPS time, anyway? I had assumed someone had simply defined GPS to be TAI - 19, and made the goal of the satellites to approximate GPS time, i.e. that GPS and TAI are the same (up to isomorphism in some category of measurements). But apparently not? Are the satellite clocks allowed to drift, or do they get corrected? -- Ashley Yakeley
Re: what time is it, legally?
My few-month old mac gives me a message saying This attachment is a type not yet supported I also get this problem on my XP at home but not on the one at my office. A newphew of mine forwarded me the reason once, and it is related to shortcuts in the email bit-pattern. I forget which software is at fault. I want to apologize for any and all technological failures of this listserve. To avoid such failures in the future, Tom Van Baak has agreed to take over its management and he is now working on the technical issues involving the migration. Demetrios Matsakis -Original Message- From: Leap Seconds Issues To: LEAPSECS@ROM.USNO.NAVY.MIL Sent: 12/12/2006 7:14 PM Subject: Re: [LEAPSECS] what time is it, legally? I'm given to wonder how much of the friction on this mailing list is simply due to the shortcomings in the technology that implements it. I've appended a message I sent in August with four plots attached. Can someone tell me whether it is readable now or was successfully delivered back then? I rummaged around on the list archive and on archives accessibly via google and find no copy of this message that survived the communications medium. On Dec 12, 2006, at 2:17 PM, Tom Van Baak wrote: Is there a technical definition of the mean in mean solar time that would help guide the discussion? See the appended message. There appears to be a natural excursion of several minutes even in the absence of first order lunar effects in accumulated leap offset over the course of several centuries. Undoubtedly an expert could wax poetic on this subject should one care to speak up. Perhaps this natural variability could be used to start to wrestle with the issue. One could argue that adding 50 or 100 leap milliseconds a few times a year (as was done in the 60's) to preserve the mean is just as valid as adding a couple of leap seconds every few years (as is done now) is just as valid as adding a couple leap hours every few thousand years (as has been proposed). I'm with you for the first two, but not the third. An approximation that is as large as the width of a timezone is equivalent to eliminating timezones. I'm not arguing for one over the other but it seems to me all three models achieve a mean. See my previous message. (Assuming it was delivered.) None of them prevent secular drift. Secular means you never zero it out. Pretending that we can get away with that is where the ALHP fails. Rob -- Begin forwarded message: From: Rob Seaman [EMAIL PROTECTED] Date: August 5, 2006 6:47:29 PM MST To: Leap Seconds Issues LEAPSECS@ROM.USNO.NAVY.MIL Subject: Re: trading amplitude for scheduling John Cowan wrote: Rob Seaman scripsit: Third result - even in the absence of lunar braking, leap jumps (or equivalent clock adjustments) would remain necessary. Why is that? If the SI second were properly tuned to the mean solar day, and the secular slowing were eliminated, there would be no need to mess about with the civil time scale, because the random accelerations and decelerations would cancel out in the long run. Of course, we'd have to tolerate larger differences between clock time and terrestrial time, but we'd expect that. Excellent discussion. The answer depends on how much larger the clock differences are, and on the meaning of the word tolerate. As Tom Van Baak said: My understanding is that, in addition to astronomical effects (lunar/solar tides), no small number of geological and climatological phenomena also contribute to the instability of the mean solar day. That all the random accelerations exactly cancel all the random decelerations in any finite time, short- or long-term, is very unlikely. Which is to say that proper tuning may not even have a definition. It certainly is non-trivial. Consider the historical trend (from http://www.ucolick.org/~sla/ leapsecs/dutc.html): ? Detrend the data by removing the 1.7 ms/cy secular effect: ? (I read the LOD from the plot every century - should repeat with the original data, but results should be acceptably accurate. I'm sure somebody would be happy as a clam to point out any errors I may have made :-) There are positive and negative excursions from normal that persist for centuries. For the purpose of civil timekeeping, we don't care what geophysics causes these excursions, or even whether the rather evident sinusoid is real or not, but just that the residual ~ +/- 5 ms length-of-day variations exist. Leap seconds represent the accumulation of these daily residuals: ? A very small daily residual becomes +/- 9 minute descrepancy between TAI and UTC over millennial time periods. So even in the absence of the secular trend, the natural geophysical irascibility of the planet is very evident. Leap seconds - both positive and negative, of course - would be needed to resync the clocks. I count about 2200 over 2500 years (for instance, about 500 leap seconds between
2006 WP-7A meeting summary
FYI this was written for distribution to all interested parties. WP 7A meeting in Geneva August 28, 2006.doc Description: MS-Word document
Re: building consensus
The answer to the intial query depends upon what you mean by active. Ron Beard, Chair of the ITU's Special Rapporteur Group is on the list. Also Dennis McCarthy, who is Chair of the IAU's Working Group on the Leap Second. I am less active, particucularly lately, but have been known to forward some emails around. We intentionally try to be silent in this forum. -Original Message- From: Leap Seconds Issues To: LEAPSECS@ROM.USNO.NAVY.MIL Sent: 06/01/2006 1:37 PM Subject: Re: [LEAPSECS] building consensus In message: [EMAIL PROTECTED] Rob Seaman [EMAIL PROTECTED] writes: : Warner Losh objects: : : There are several doughty people here who happen to have that : opinion, but they abide with us mortals outside the time lords' : hushed inner sanctum. : : I have spent much time explaining why leap seconds cause real : problems in real applications, only to be insulted like this. : : Sincere apologies for my awkward statement. Dictionary.com defines : doughty as marked by stouthearted courage; brave. I wasn't : questioning the knowledge or passion of folks holding views that : differ from my own. Rather I was attempting to question whether : anybody actively participating on this list - holding whatever view - : is also participating in ITU discussions. : : I see that Mr. Cowan has also parsed my admittedly opaque remarks. Yes. I'm sorry I was so easily offended. Please accept my appologies for my hasty words. Warner
FW: [LEAPSECS] ABC leapsec article
There is a nifty google feature that will scour the internet for news articles on any subject, and send you weeky, daily, or immediate notifications. Browse on http://www.google.com/alerts Beware- If you ask for 'leap second' you will get more than you want! Ask for leap second, and you will get emails like what is below. *** From: Google Alerts To: [EMAIL PROTECTED] Sent: 11/09/2005 6:08 PM Subject: Google Alert - leap second Google Alert for: leap second No http://www.heise.de/english/newsticker/news/65971 more leap second? Heise Online - Hannover,Germany ... Telecommunications Union ITU is meeting this Wednesday and Thursday in Geneva to discuss, among other things, the future of the leap second, which is added ... _ This once a day Google Alert is brought to you by Google. Remove http://www.google.com/alerts/removx Create http://www.google.com/alerts?hl=en another alert. Manage http://www.google.com/alerts/manage?hl=en your alerts.
ITU Meeting last year
This is a very brief description of what happened at last October's ITU meeting in Geneva. A resolution was proposed to redefine UTC by replacing leap seconds by leap hours, effective at a specific date which I believe was something like 2020. This proposal was not passed, but remains under active consideration. Presumably something like it will be considered next year. My quick computation indicates that, should this proposal be adopted, it would take about a century for UT1-UTC to diverge by one minute, and many centuries before a leap-hour would be called for. I did not attend the meeting, and this is all I know. I was told the ITU web pages had essentially this same information in them, but could not find anything there with their search engine.
