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    Re: Navigation without Leap Seconds
    From: Geoffrey Kolbe
    Date: 2008 Apr 21, 19:43 +0100

    
    
    
    >Response from George- NavList 4880
    >
    >I wonder how confident Geoffrey really is about that projection into the
    >future, to within a second "or so".
    
    
    As ever, thanks to George for his thoughtful and thought provoking piece on
    Delta T.
    
    Alas, I did not write the software program which I used to derive my
    tables. I used the Stormy Weather 'Astro' program written by Paul
    Adamthwaite (www.stormy.ca) to derive the quadrennial coefficients.
    
    Prodded by George, I contacted Paul Adamthwaite and asked him for his
    latest thinking on the Delta T problem and its impact on his program - and
    on my almanac in consequence. It turns out that there is quite a bit of
    interest from a number of other concerns on the Delta T matter and Paul has
    been researching the matter in some depth. Indeed, he is giving a talk on
    the subject as part of the celebrations marking upcoming centenary of the
    Canadian Navy.
    
    Paul is currently awaiting feedback from the Paris Observatory, who have
    been doing a lot of theoretical modelling on the Delta T matter. Paul says
    there is now a much better understanding of the Delta T problem and there
    are theorists who are confident that that they can predict Delta T to an
    accuracy of about two seconds over the next fifty years. But - pending the
    outcome of the Paris Observatory's deliberations - Paul feels an error
    margin of ten seconds is one with which he feels more comfortable.
    
    A second edition of my Long Term Almanac 2000 - 2050 is currently being
    prepared. I will be inserting a caveat on the matter of Delta T and a
    warning about the possible abolition of leap-seconds in this edition.
    
    George's Delta T = 0 for the epoch of 1900 for a current value of 38
    seconds for Delta T seems to be adding to the chaos which he feared with
    different time systems. In such literature as I have read on the subject, a
    value of 24.349 is used for the 1900 epoch, with a current value of about
    65 seconds. See, for example, ftp://maia.usno.navy.mil/ser7/deltat.preds I
    would be interested to know where George got his value for Delta T.
    
    Geoffrey Kolbe
    
    
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