[LEAPSECS] LEAPSECS Digest, Vol 45, Issue 4

Ian Batten igb at batten.eu.org
Thu Sep 2 17:57:20 EDT 2010

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.

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