[LEAPSECS] LEAPSECS Digest, Vol 45, Issue 4

[Ian Batten]

On 2 Sep 2010, at 22:20, Finkleman, Dave wrote:


> However, I don't see where judgement enters into the mandate for UTC.

> It says UTC.  There might be a call on whether it was UTC before the

> change or after.  There might be a debate over whether DoC had

> authorized it, but it is still UTC.


I think that there would be a perfectly reasonable debate as to if it  
meant UTC as defined at the point of legislation or UTC as currently  
defined.   This is why US common measure and UK imperial measure  
diverged: the UK passed legislation in 1824 to systematise it, while  
the US system is based on earlier practice.  Not merely do we have a  
different number of fluid ounces in a pint, our fluid ounce is  
different too.   So in that case, at one point US law incorporated an  
external standard, but then when that external standard changed, the  
US law continued with what it had incorporated.

I think the basic argument would run that UTC classic is for practical  
purposes a solar timescale, but has some useful properties (constant  
seconds, for example) which outweigh the problems (leap seconds).  The  
proposed new UTC has some of those desirable properties, but isn't a  
solar timescale.  I think I'm right in saying that practical astro- 
navigation ignores DUT1 because the inherent precision of the  
processes is less than the effect of 0.9 seconds, although I'd welcome  
correction; that's clearly less true as DUT1 increases and progressive  
error comes into measurements of longitude with clocks set to new UTC.

If UTC has been adopted because it's both uniform and solar, and one  
of those properties ceases to be true, that may (or may not) present  
an issue worth arguing about.

ian
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