UT1 vs. UT2

From: Steve Allen <sla_at_ucolick.org>
Date: Thu, 5 Jun 2003 13:29:44 -0700

On Thu 2003-06-05T13:10:10 -0700, Brian Garrett hath writ:
> time on birth and death certificates is important, but I was not aware of
> how important until I saw a posting from Prof. David Mills on
> comp.protocols.time.ntp in which he said that UT1 (not UTC) is the legal
> standard for death certificates.

The US Code currently specifies mean solar time on 15 degree meridians
west of Greenwich. At the time that the US Code was last revised,
broadcast time signals in most of the world provided UT2, not UT1. So
I would offer that at a sub-second resolution UT2 might be the legal
time in the US because it is more "mean" than UT1.

Note that the old expression for UT2 is still prominently displayed
on the main page of the Earth Orientation Department of the US
Naval Observatory
I don't really understand why it is there, except as a historical

If it were to be used today, the old expression would best be
replaced by a newer one based on the mean orbital motion used in
the most recent IAU nutation model and on seasonal earth rotation
variations as measured by VLBI over the past 20 years.

On the other hand, at the level you can time a death, birth, traffic
accident, crime, financial transaction, or whatever, one second is
about as good as could be civilly relevant. At that level, UT0, UT1,
UT2, GMT, and UTC are currently indistinguishable. There are probably
very few tests of legal issues at a finer resolution.

And that is why UTC, despite the unilateral power grab at its origin,
has been such a useful timescale for the past 30 years. It has SI
seconds, and does not deviate in value by more than a second from the
historical civil and legal understanding of "time-of-day".

I've grown accustomed to tuning into WWV and hearing them announce
that they provide
    time of day, standard time interval, and other related information
It would be disappointing to hear it change to
    atomic time, standard time interval, and other related information

Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla_at_ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93
Received on Thu Jun 05 2003 - 13:30:03 PDT

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