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>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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