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

[Rob Seaman]

A white paper on legal ramifications is available at:

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

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

Rob Seaman
National Optical Astronomy Observatory
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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