[tz] isdst bug Europe/Dublin (tzdb-2019c)

[Michael H Deckers]

    On 2019-12-16 19:03, Brian Inglis wrote:


> Just to muddy things further, in an article in "Polar Motion: Historical and
> Scientific Problems", ASP Conference Series, Vol. 208, also IAU Colloquium #178.
> Edited by Steven Dick, Dennis McCarthy, and Brian Luzum. (San Francisco: ASP)
> ISBN: 1-58381-039-0, 2000., "History of the Bureau International de l'Heure",
> Guinot, B., p.181:
>
> 	http://articles.adsabs.harvard.edu/pdf/2000ASPC..208..175G#page=7


    Thanks for the reference!


> ...so all should bear in mind that TAI is a synthetic timescale calculated and
> adjusted in arrears, so shares some of the same problems as leap seconds but
> occurring at higher precisions.


    "adjusted in arrears":
       The definitive values of TAI are fixed about a month after the fact
       (fast in astronomical terms!) by Circular T. A more uniform time 
scale
       can be obtained when more than a month's future data are used; such
       evaluations are done by the BIPM and published yearly as estimates
       TT(BIPM xx) of TT.

    "same problems as leap seconds":
       I do not think so. That is, no astronomical observations (eg,
       satellite orbits, pulsar timings) can currently reach or exceed
       the accuracy of the determination of TT with earth-bound clocks,
       and the upcoming use of optical clocks will lead to a significant
       increase in accuracy. Nor is there any sign of a systematic
       difference in rate between TAI and TT -- it would be "new physics",
       I guess.

     Michael Deckers.