[LEAPSECS] Leap smear

[Clive D.W. Feather]

Rob Seaman said:

>>> If you don't believe that civil time is time-of-day where "day" means "synodic day", then assert an alternate definition for what the word day means.



>> I don't "believe" it. I *know* that a "day" is the length of time it takes the little hand of the clock to rotate completely twice. Or, more precisely, the specific clock at NPL.

> 

> So would you assert that the NPL has the freedom to adjust that clock to any rate it chooses?


No, because NPL has agreed to keep that clock running at two rotations per
794243384928000 periods of the radiation corresponding to the transition
between the two hyperfine levels of the ground state of the cesium 133 atom.


> (I "presume" that my point about engineering requirements was made several years ago, though empirical evidence is slight :-)


I actually have no problem with your call for engineering requirements.
Though I'd like to know where they were when the leap second was invented.


> > Actually, as we've discussed here ad nauseam, where I live the "day" is de jure the mean solar day at Greenwich and de facto 794243384928000 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

> 

> These assertions are both de jure, both specifications.


Not for what "de jure" means to me. The latter definition is one of
convenience to me; it is *not* one of law in any shape or form.


> The underlying requirement is not something like "thou shalt honor mean solar time at Greenwich".


Quote correct. Glad to see you finally admit this isn't a requirement.


> Another way to state the underlying requirement is that calendars count integral days.  Points awarded for anybody who can make this work for some definition of day that does not remain stationary with respect to mean solar time.


    '"day" is defined as 794243384928000 periods of the radiation
     corresponding to the transition between the two hyperfine levels of
     the ground state of the cesium 133 atom.'

What was hard about that?


> An engineering requirement is not a specification.


Agreed.

However, nor is it an axiom. There's nothing magically correct about the
synodic definition of "day", any more than there's anything magically
correct about the TAI or UTC definitions of it. Which we choose to use for
civil time in any particular place is purely a question for the politicians.

-- 
Clive D.W. Feather          | If you lie to the compiler,
Email: clive at davros.org     | it will get its revenge.
Web: http://www.davros.org  |   - Henry Spencer
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