Re: [LEAPSECS] Leap-second scare stories

From: Markus Kuhn <Markus.Kuhn_at_cl.cam.ac.uk>
Date: Sat, 30 Jul 2005 17:55:28 +0100

"John.Cowan" wrote on 2005-07-30 15:35 UTC:
> > Let's not forget that this proposal is all about replacing a
> > reasonably frequent minor distruption (UTC leap seconds) with a very
> > rare catastrophically big one (UTC leap hours).
>
> No, it's about replacing an irregularly scheduled minor glitch in
> what should be a uniform time scale with irregularly scheduled
> major glitches in time scales (the 400-odd LCTs worldwide) that
> no one expects to be either uniform or predictable, but where
> measures to deal with these problems are already very much in place.

We must be talking about different proposals then. The one discussed by
the WSJ article is, as I understood it, the one submitted by the US
delegation to ITU-R working party 7A on 1 September 2004
(Document 7A/15-E), which I understand to be identical with:

  http://www.cl.cam.ac.uk/~mgk25/time/leap/PropRevITU-RTF460-6.pdf
  http://www.ucolick.org/~sla/leapsecs/PropRevITU-RTF460-6.doc
  http://www.ucolick.org/~sla/leapsecs/gambis.html

This one very much proposes to introduce leap hours into UTC, to be
announced by IERS 5 years in advance (page 8):

----------------------------------------------------------------------

1 Tolerance

The difference of UT1 from UTC should not exceed 1 h.

2 Adjustments to UTC

2.1 Adjustments to the UTC time scale should be made as determined by
the IERS to ensure that the time scale remains within the specified
tolerances.

2.2 The IERS should announce the introduction of an adjustment to the
UTC time scale as least five years in advance. At the time of the
announcement the IERS should provide directions regarding the details of
the implementation of the adjustment.

2.3 All operational rules and nomenclature prior to 0000 UTC December
21, 2007 given above no longer apply.

Notes:

(1) The broadcast of DUT1 will be discontinued.

(2) Analysis of historical observations of the Earth's rotation
currently indicates that such an adjustment would not be required for at
least 500 years.

----------------------------------------------------------------------

I have only mild objections to simply going straight to atomic time
(e.g., the TI proposal that was discussed at Torino). But a proposal
like the one on the table at present, which attempts to camouflage the
move to atomic time as merely a simple relaxation of the UTC tolerance
by a factor 4000 from |UTC-UT1| < 0.9 s to |UTC-UT1| < 1 h is a recipe
for catastrophes and therefore unlikely to ever be implementable. I
consider such proposals illegal under Truth-in-Advertising legistation.
They are a political trick. They are an attempt to make the change to
UTC look less severe than it really is.

If someone submits a proposal for discontinuing leap seconds, then it
should say that |UTC-UT1| will from now on be allowed to grow unbounden,
and they should choose a name that does not contain the astronomical
term "Universal Time".

Markus

--
Markus Kuhn, Computer Laboratory, University of Cambridge
http://www.cl.cam.ac.uk/~mgk25/ || CB3 0FD, Great Britain
Received on Sat Jul 30 2005 - 09:55:41 PDT

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