[LEAPSECS] "China move could call time on GMT"

[Warner Losh]

On Dec 31, 2011, at 6:32 AM, Rob Seaman wrote:


> A white paper on legal ramifications is available at:

> 

> 	http://futureofutc.org/preprints/04_AAS_11-662_Seago.pdf


This talks about the differences between DUT1 exceeding at most an hour.  The current proposal doesn't have leap hours in it, nor were they anticipated by my remarks.  My remarks were aimed at the idea that as the time drifts too much people just pick a new timezone, thus keeping time to within an hour over the extremely long haul.  This is no different than people adding leap days to keep the equinoxes within a few days of the 20th.  We don't worry that we can be as much as two and a half days out, and we don't worry that the slowing rotation of the earth will render the Gregorian calendar out of spec after about 10k years.


> with conference slides and transcribed discussions at:

> 

> 	http://futureofutc.org/program/presentations/AAS_11-662_Seago.ppt.pdf and

> 	http://futureofutc.org/preprints/05_AAS_11-662_discuss_2.pdf

> 

> It might also be productive to wonder what would happen to the concepts of "Universal Time" and "Greenwich Mean Time" themselves should the ITU proposal be adopted.  Look at the subject line of this thread for an example - UTC is nowhere in sight.  This list has spent a dozen years debating overtly technical details using terms of art like UTC and UT1.  The public will naturally conflate these with just plain UT and GMT.

> 

> Note that the ITU proposal makes no mention of this notion of an hour tolerance that some have batted about as fact.  It simply turns UTC into TAI with an offset.  Whatever our diverse opinions on the subject, could we at least discuss what is actually proposed:

> 

> 	http://www.ucolick.org/~sla/leapsecs/draftTF460-7nt.html


The hour tolerance is for civil time, not UTC.  Civil time has, and always will be, UTC + offset, where offset is defined by countries.  Those countries that have "mean solar time" could choose to interpret that as having an hour tolerance to the new  timescale if the ITU proposal passes.  That's why I specifically said noted that at least some of the countries that have mean solar time written into their laws don't have 'mean solar time' but rather 'mean solar time as interpreted by $OFFICIAL.'  This means that as international definitions and conventions change, these officials have the power to interpret old laws under new rules.  As the definition for UT1 has changed and evolved over the years, officials rubber stamped that.  As people moved to UTC instead of UT1, officials interpreted UTC as an acceptable mean solar time, even though it isn't quite a mean solar time, and introduces either a discontinuity (the leap second) (using the old, pre ITU definition of time of day) or introduces an irregular radix (under the new ITU definition of time of day).  Before the US congress changed the law to UTC, the US's official time as published by NIST, was UTC even though the law said 'mean solar time.'  The reason for this was that it was mean solar time as interpreted by the secretary of commerce.  The secretary delegated time to NIST who said UTC is mean solar time, for the purposes of the law.

I'm postulating that similar weasel words exist that would allow other countries to follow the same 'fiction' because that's the new interpretation.  It has nothing to do with what astronomers think is the right definition, but rather it has everything to do with what bureaucrats decide is the right definition...

Warner


> Rob Seaman

> National Optical Astronomy Observatory

> --

> 

> On Dec 30, 2011, at 10:42 PM, Warner Losh wrote:

> 

>> Which countries define their legal time to 0.1s of MST?  When you start tossing in terms like "good faith" into the definition, then you can no longer say 0.1s, since the two definitions are opposed.  Either it is within 0.1s of some specifically defined time, or they use weasel words like the old US law "Mean Solar Time ... as determined by the Secretary of Commerce, or his designated deputy."

>> 

>> Even in the UK, where time is supposed to be GMT cannot possibly realize GMT anymore since the prime meridian no longer passes through any recognized observatory to realize GMT.  This creates a legal ambiguity where UTC is published by the government labs, but the delta between GMT and UTC is only known retrospectively (although proactive predictions can be only an order of magnitude less accurate for short time periods).  So while the law may state one thing, the facts on the ground favor something else because the two are close.  The proposed ITU changes to UTC will only muddy the waters more, not less, as the old approximation GMT == UTC will cease to exist.

>> 

>> And besides, who is to say that a mean solar time, averaged over hundreds of years, with a tolerance of on hour wouldn't be one possible reading of the british law?

>> 

>> Warner

> 

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