[LEAPSECS] drawing the lines

[Rob Seaman]

Hi Kevin,


> I'm still puzzled at the reasons for stating that UT1 should not be considered as a time scale in this recommendation.  How does that serve this recommendation?  This is a bit of a different question from evaluating UT1 as a time scale.  Instead, it is a question about the reasons why the evaluation of UT1 must be included in this recommendation.  Does saying that UT1 is not a time scale strengthen the other points in any way?  Is it necessary for the other points to be accepted?   



It is a "statement against interest" as they say in the courts, an implicit admission that two different timescales are required (in the engineering sense).  The authors don't want to call Universal Time a time scale (in its avatar as UT1 or otherwise), but they can't eliminate the concept.

Hence also the attempt to subdivide UTC into three separate terms:  "Coordinated" + "Universal" + "Time", rather than the two terms it represents in historical and the worldwide current context:  "Coordinated" + "Universal Time".  This is emphasized by UT1 itself, because by the same logic it would be "Universal" + "Time" + "1", which is obviously a time.  See, for example, the next bullet:

	10. the International Earth Rotation and Reference Systems Service (IERS) provides a means of accessing UT1 in real-time by means of routinely available predictions of UT1-UTC with precision 100 000 times better that the coarse approximation UT1 = UTC currently provided by means of coding UTC to match UT1 within 0.9 second;

To quote a friend:  "If UTC is time, and if UT1 is angle, then what is (UT1-UTC)?  How can one subtract angle from time and have a meaningful result, without both being instantiations of the same concept?"

There has been an attempt to redefine the language for years, since an earlier revision of ITU-R TF.460 was edited to remove the original language:

	"GMT may be regarded as the general equivalent of UT."

Leap seconds are a means to an end, which is to root civil timekeeping in mean solar time - that is, in the synodic day.  By all means lets discuss alternate ways to implement this, but simply declaring that Universal Time no longer exists as a concept is a non-starter.  We will reach consensus more quickly by first seeking common language and concepts.  If a new concept is needed, define a new term.

Rob

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