Re: [LEAPSECS] Mechanism to provide tai-utc.dat locally

From: Steve Allen <sla_at_UCOLICK.ORG>
Date: Fri, 29 Dec 2006 00:06:54 -0800

On Thu 2006-12-28T18:31:43 -0700, M. Warner Losh hath writ:
> Let's turn the question around. What would the harm be if |DUT1| were
> 1.1s? 1.5s? 2.0s? Contrast this with the harm and difficulty that
> the current 6 month scheduling window affords.

I have previously indicated that I believe this proposal is workable
even with a full decade of lookahead.

I don't think there is much harm. From a technological standpoint
I think we can handle it if we are given a decade of advance warning.

Because the current form could not accommodate the new magnitude it
would demand discontinuation of DUT1 signals in the broadcasts of
time, but this is not harm. I believe that there is not one person
objecting that the broadcasts of DUT1 are being used by anyone.

For our existing telescopes at Lick, no harm. The biggest is
literally battleship-era technology -- built by the foundries looking
for post-war reasons to keep producing large steel objects, and it
steers about as well as a battleship. I do not believe we have any
software that would fail with larger values of DUT1.

For celestial navigation, no harm other than to require use of one
more correction in the almanacs. The projected values of UT1 as
published in annual almanacs would almost certainly be as accurate
as the DUT1 broadcasts have been. As seen in vol 2 of MNRAS, the
Admiralty forced worse changes of procedure on sailors 174 years ago.

For the newest telescope now being built at Lick there might be harm,
but we can't tell. It's pointing will rely on ingesting the file
using software for which we will not have the source code.

This could be an issue for us and for any other agency using that
file because nobody can guarantee the formatting rules of the
file provided by USNO. If it is being produced by Fortran then
it will fill its field widths as soon as UT1 - UTC reaches -10
seconds. This would be a problem for interpreting software which
was relying on space separation rather than fixed-width fields.
We intend to request that the vendor rely on obtaining the data from
a file whose format is formally specified instead of hoping that
the USNO can and will continue providing that old format which is
not an official IERS data product (it predates the IERS).

But I would be uncomfortable with this proposal unless I were
to see more definitive changes in the responsibility for UTC.
The final words in the summary of the 2003 Torino colloquium were
        Responsibility for disseminating UT1 information should remain
        solely with IERS.
The time scale(s) in use by most of the world should not be held by an
organization which cannot openly publish the characteristics. I think
that the ITU should not only get out of the business of distributing
UT1, but out of the time scale business altogether.

I think that the ITU-R document should restrict itself to naming a
time scale whose characteristics are entirely under the control of
another agency -- an agency which can openly publish the
specifications. Right now the ITU-R document reads
        UTC is the time scale maintained by the BIPM, with assistance
        from the IERS
which makes for a very fuzzy division of responsibility. I think all
responsibility for UTC should be delivered to IERS. I would change
ITU-R TF.460 such that it had no annexes at all and basically ended
with the words
        UTC is the time scale maintained by the IERS in conjunction
        with the BIPM.
And with that in place I don't really care whether the ITU-R decides
that it is better to broadcast UTC or (TAI - n). If the ITU-R
later deems that the external agencies maintaining those time scales
are not following rules suitable for broadcasts then they can change
the document to name yet another time scale.

In one sense this would put a great deal of responsibility onto the
IERS, but for practical purposes that is already the case. Maybe it's
not workable for the IERS to have full responsibility; it's purely
scientific and there's no direct democratic structure. The BIPM is
constrained by the resolutions of the CGPM and its international

But really, when it comes down to it, people are probably in general
agreement that it shouldn't be necessary to rely on either scientists
or international diplomacy to tell them when the sun is up.

Steve Allen                 <>                WGS-84 (GPS)
UCO/Lick Observatory        Natural Sciences II, Room 165    Lat  +36.99858
University of California    Voice: +1 831 459 3046           Lng -122.06014
Santa Cruz, CA 95064     Hgt +250 m
Received on Fri Dec 29 2006 - 00:07:49 PST

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