[LEAPSECS] Changing the name of UTC

[Steve Allen]

On Thu 2014-10-16T22:02:02 +0000, Matsakis, Demetrios hath writ:
> Con: The ISO has 290 committees, which people frequently disagree
> with and are not bound to follow.  In this case the advisory opinion
> goes against the standard metrological practice of not changing names.
> The best example is UTC itself when frequency steers to UT1 were
> eliminated.  Also the meter, which went from a physical meter bar in
> Paris to the product of the speed of light with the SI second.  And
> the kg, which is about to be redefined but no one is suggesting a name
> change.  Another example where changing the name would have caused
> confusion is the 2006 redefinition of the term "planet".

People are not bound to follow ITU-R recommendations either.  For
example, the GPS system time broadcasts something not recommended, as
do Galileo and BeiDou.  The ATSC spec for television in North America
and the IEEE 1588 (PTP) standard have also chosen to eschew the time
scale of the ITU-R in favor of a time scale in almost all cases
actually based on GPS.

If I ask the question "Is Pluto a planet?"  I know where I can find
the authoritative answer.  The proceedings from the IAU GA in 2006
make it clear that the answer is "no".

If I ask the question "Is Universal Time a measure of earth rotation?"
I can find the authoritative answer in the proceedings from many
different IAU General Assemblies over an interval of more than half a
century.  The answer is "yes", and the same answer is present in
textbooks stretching over several centuries, and Louis Essen (inventor
of the cesium chronometer) agreed.

If I ask the question "According to civil time how can I tell when one
calendar day ends and the next begins?"  the answer is when the clock
goes from 23:59 to 00:00.  Looking more closely at the body of
documentation about UT and UTC it is clear that the leap second was
instituted in order to satisfy the dual demands that radio broadcast
time signals must provide cesium atomic seconds while also providing
days based on Universal Time.

While it was documented explicitly that was because UT is a measure of
earth rotation inherent in contemporary celestial navigation, it would
be wrong to assert that people were blind to the fact that UT was also
the measure of calendar days since antiquity.  It appeared for a while
as if the CCIR had managed to kill two birds with one stone.

The difference between redefining the meter and redefining UTC is that
there is a single concept underlying length, but there are two
incommensurate concepts underlying UTC.  Redefining the meter makes it
better for everyone to measure length.  The notion of redefining UTC
without leap seconds makes it better for measuring duration in seconds
and useless for measuring earth rotation in calendar days.

It is no longer practical to kill the two birds with one stone.
But it is also wrong to assert that one of the birds is dead.
Measuring earth rotation remains a valid and necessary practice
distinct from measuring cesium atoms, and there are ways to count
SI seconds while also keeping calendar days based on the earth.

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