[LEAPSECS] Leap smear

[Steve Allen]

On Mon 2011-09-26T21:11:08 +0100, Ian Batten hath writ:

> Why is 1s acceptable and 10s not?


A change will break existing software and systems in astronomy,
astrodynamics, and other fields, possibly even legal ones.  Those
systems were based on documents specifying the constraint of 1 s.


> When UTC was first confected, the bounds weren't defined like that.


In the context of international standards there was no such thing as
UTC until 1974.  There was something widely referred to as UTC before
leap seconds, but it was understood to be more like what are now known
as IETF RFCs designated as "Best Current Practice", not a "Standard".
The implementation of anything called UTC prior to 1972-01-01 can
hardly be used as justification for any further decisions.

In Document VII/1008 from CCIR International Working Party VII/I (aka,
Interim Working Party 7/1, because the CCIR did not use a consistent
notation for its own procedures) for the 1970 Plenary Assembly section
2 of the draft originally included the phrase "or integral multiples
thereof".  The Plenary Assembly deleted those words.  As is the case
with much of the activity of CCIR and ITU-R, no record exists of the
discussion about this change nor its intent.

The clearest picture of the sorts of discussions regarding CCIR Rec
460 come from the 14th General Assembly of the IAU later in 1970.
Those indicate concern that a deviation of more than 0.1 s could be
problematic.

The association of the name UTC with leap seconds did not appear in
official form until CCIR Rec 460-1 in 1974, but in that and all
subsequent pronouncements about UTC from other agencies it was made
clear that UTC provides a form of mean solar time within 1 s of UT1.

We mash words here in diplomatic(?)  jousts over treaty obligations or
lack thereof.  The desired technical result can be accomplished simply
by (again) changing the name of the internationally approved broadcast
time scale if its characteristics are (again) changed.

--
Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
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