[LEAPSECS] Leap smear

[Rob Seaman]

On Sep 23, 2011, at 11:00 PM, Clive D.W. Feather wrote:


> 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?  An appeal to authority is almost always a statement about a specification characterizing a particular solution, not a requirement characterizing the problem space.

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


> 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.  The underlying requirement is not something like "thou shalt honor mean solar time at Greenwich".  Not to mention that specifications rarely trace one-to-one to even the most seemingly analogous requirements.

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.  By all means let's discuss the fine points, but please review vast numbers of messages regarding the irrelevancy of apparent time and daylight saving time,  and about the distinction between periodic and secular effects.

An engineering requirement is not a specification.  Precision is not accuracy.  The ITU proposal is not a coherent system engineering plan.

I'm reading Dava Sobel's excellent new book on Copernicus, "A More Perfect Heaven", and have reached the point where Rheticus grasps that Copernicus is actually stating that the Earth rotates on its axis and orbits the Sun.  That is - that the Earth physically moves, not that he is just proposing some better computational technique.*  We are having the same conversation.

Rob

* More fundamentally even yet, Copernicus pushed the sphere of the stars to a dramatically greater distance.  The Copernican universe was vastly larger and more grand than the Ptolemaic.