Re: [LEAPSECS] A lurker surfaces

From: Magnus Danielson <magnus_at_RUBIDIUM.DYNDNS.ORG>
Date: Wed, 03 Jan 2007 06:33:20 +0100 (CET)

From: Rob Seaman <seaman_at_NOAO.EDU>
Subject: Re: [LEAPSECS] A lurker surfaces
Date: Tue, 2 Jan 2007 20:45:14 -0700
Message-ID: <13456BAE-A7D3-47C8-BB39-D797D4EBF6F0_at_noao.edu>

Rob,

> Magnus Danielson wrote:
>
> > If you do want a new timescale, I think rubber seconds isn't going
> > to be the solution.
>
> One might point out that many time scales do rely on rubbery seconds,
> e.g., sidereal time and apparent solar time. If might be
> enlightening to step back from the tendentious and tedious tug-of-war
> between UTC and TAI and reflect that even UT1 - a mean solar time
> scale - intrinsically has rubber seconds. Sexagesimal notation is
> clearly revealed as a way to express an angle - of Earth orientation
> in this case. The whole point of UTC is to permit Earth orientation
> to be approximated while using SI seconds.

Indeed. The civil usage require something like UT1 even if not precise UT1.
UTC is one such solution. UT1 is as rubbery as it gets. Some transmissions
include enought information for creating a local estimate of UT1, but not with
sufficient level of resolution for all the uses we have. With the one-way
(or indeed two-way) time transfer mechanisms now at our disposal we can remove
much of the time offset between transmitter and receiver. You could therefore
build UT1 realizations based on improved clock model and diverse parameters for
UT1 realization. Technically it would be quite possible. You "just" need to add
these parameters in order for a TAI/UTC transmission or for that matter UT1
transmission (with transmitter corrections). Even if rubbery, you should be
able to build an smoothed UT1 realisation of quite high accuracy if you need
to. However, this would result in several problems not only in the updating of
the transmission system and the related receivers, for many other purposes we
still require TAI traceability/stability as well as "civil time" alongside.
With all its thorns UTC is IMHO a better solution than having to deal with
two different types of seconds which moves around all the time.

I view your comment as being astronomy-oriented (nothing wrong with that).
However, for the type of systems which I normally wrap my head around the exact
angle of Earth orientation is as such not very interesting, but on average it
needs to be somewhere in the neighborhood of UT1 in the long run.

There are usage for TAI, UTC and UT1. Do we need to invent one more? Do we need
to make wider useage of UT1? Are the problems of UTC really that big? IMHO and
to the best of my limited insight I still find those questions answered with a
no.

Cheers,
Magnus
Received on Tue Jan 02 2007 - 21:33:48 PST