Re: [LEAPSECS] what should a time standard encompass?

From: William Thompson <thompson_at_ORPHEUS.NASCOM.NASA.GOV>
Date: Mon, 27 Jan 2003 10:17:48 -0500

"Seeds, Glen" wrote:
> Although this is (as Ken says) a long and somewhat rambling dissertation, I
> agree with almost all of the points made (many of which I haven't seen yet
> in this forum).
> The one statement that I have some concerns about is this one:
> > (3) Searching for a better way of addressing the two major categories
> > of precision time needs that UTC attempts to reconcile,
> > ... is what I had originally
> > hoped LEAPSECS would be about. Alas, it appears to not be. :-(
> I'm not aware that there are "two major categories of precision time needs".
> As I see it, there is only one category of (absolute) precision time need,
> which is satisfied by TAI. UTC and its derivatives are useful for civil
> time, not because they are precise, but because they are derived from TAI.

But there are two such categories. Astronomy and astronomical navigation depend
on precision time tied to Earth's rotation--i.e. UT0, UT1, and UT2--while other
needs are well met by TAI. The purpose of UTC is to serve as a bridge between
the various astronomical UT times and TAI. Loosing that bridge will be a major

There's been a lot of talk in this forum about civil time, and what it will be
like millenia from now. I find most of that talk rather silly. What tends to
get ignored is that changes to the UTC time standard will make themselves felt
in the astronomical and astronavigation community not in comfortably far away
millenia, but in mere decades. It will affect not only professional
observatories, but millions of amateurs who don't have the resources that
professionals have access too.

William Thompson
Received on Mon Jan 27 2003 - 07:27:58 PST

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