Re: [LEAPSECS] UT1 confidence

From: M. Warner Losh <imp_at_BSDIMP.COM>
Date: Thu, 18 Jan 2007 00:40:56 -0700 (MST)

Steve,

thank you for this enlightening report.

In message: <20070118071144.GA15069_at_ucolick.org>
            Steve Allen <sla_at_UCOLICK.ORG> writes:
: On Wed 2007-01-17T12:31:14 -0700, Warner Losh hath writ:
: > It has been remarked that the current state of the art is that 100ms
: > accuracy can be predicted about a year in advance only and that the
: > models are constantly undergoing refinement. It has been estimated
: > that IERS could issue leap seconds, with today's technology, about 3-5
: > years out and still be in a 95% or 99% band of certainty that the 0.9s
: > margin is maintained. However, I can't find papers that show these
: > models or point to any better data than hearsay...
:
: The best that I know of were the ones presented at the Colloquium that
: the WP7A SRG held in Torino in May 2003. There was a time when the
: host institution (IEN) was providing the proceedings online, but the
: contents of that URL went away sometime around a year ago. (I wonder
: if they may not have liked the conclusion that was reached.)
:
: In the spirit of promulgation I provide what they once did at
: http://www.ucolick.org/~sla/leapsecs/torino/ITU.shtml
:
: The conclusion was originally a powerpoint drafted in real time, it is
: http://www.ucolick.org/~sla/leapsecs/torino/closure.pdf
:
: The indications of how well predictions of UT1 might be done are found
: in three presentations to which Felicitas Arias contributed.
: There are two which were powerpoint
: http://www.ucolick.org/~sla/leapsecs/torino/guinot.pdf
: http://www.ucolick.org/~sla/leapsecs/torino/arias_2.pdf
: and one which is a more verbose writeup of one of the powerpoints
: http://www.ucolick.org/~sla/leapsecs/torino/arias_3.pdf

I like figure 8, that shows that 20ms steps lead to 50ms steps lead to
100ms steps lead to 1s steps. :-)

I also like the quotes:

"Dating in UTC is ambiguous when a positive leap second occurs in
systems other than those using hours, minutes and seconds; in this
latter system the use of second "60" may a cause of difficulty."

and

"Thus UT1 is not, strictly speaking, a form of solar time"

Also, did I miss figure 9 in arias_3?

Proposal II has gotten much press here (the leap hour one), but
Proposal I sounds a lot like what I've suggested: Use TAI time and let
countries move the time zones when they feel like they no longer are
close enough, but it kinda omits that last part...

Warner
Received on Wed Jan 17 2007 - 23:43:34 PST

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