Re: [LEAPSECS] UT1 confidence

From: Rob Seaman <seaman_at_NOAO.EDU>
Date: Thu, 18 Jan 2007 01:07:33 -0700

Steve Allen wrote:

> The plots by Arias indicate how well UT1 could have been predicted
> over two and three year intervals for the 40 year interval starting
> around 1960. It is based on those plots that I have voiced no
> concerns for the pointing of our telescopes if leap seconds were
> published five years in advance. I'm not ready to go for ten.

It appears to this observer also that a consensus for extending leap
second scheduling from a six month interval to a five year interval
should be straightforward to achieve. This is a factor of ten
improvement, could be later lengthened as the state of the art
allows, is likely already supported under the standard, and might in
practice require no coarsening of the 0.9s maximum tolerance -
especially if the five year lookahead were combined with the freedom
to schedule each intervening leap second at the end of any month.

Whether this would be the consensus - or whether some other
scheduling algorithm - the first step would be to take the divisive
and dangerously naive leap hour proposal off the table. It is
exhausting and distracting to have to continually fend off this rabid
turkey. The wisdom of taking the time and making the effort to form
a robust consensus BEFORE changing civil timekeeping policies cannot
be overestimated.

I would, however, like to better understand what Arias means by
"empirical linear prediction". This appears not to rely on any
physical model of the rotating Earth. Surely the plots referenced
should be taken as worst cases? One would also want to combine these
predictions with the details of specific scheduling algorithms to
start to understand the trade-offs and what the practical limits
would be on the range of DUT1.

Rob
Received on Thu Jan 18 2007 - 00:08:28 PST