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    Re: Ut=Gmt?
    From: Geoffrey Kolbe
    Date: 2010 Mar 26, 17:13 +0000

    At 15:40 26/03/2010, you wrote:
    The almanacs today consistently use the term Universal Time (UT) to tabulate data.  Older ones use the label GMT (Greenwich Mean Time).  I know that "a rose by any other name..." but what do NavList members think of this terminology?


    Peter Hakel

    P.S.  Here is what Meeus writes in Chapter 10 of his Astronomical Algorithms:

    Universal Time is erroneously called "Greenwich Mean Time" in Great Britain and by most navigators.  ...  It is the civil time which begins at midnight, so GMT and UT differ by twelve hours.

    In 1925 the change was made to define the day in the almanacs as starting from midnight instead of noon. GMT effectively ended here.

    And today, where we have leap seconds introduced into UTC (broadcast time) to bring it into line with UT1 (time as determined by astronomical observations) we definitely do not have GMT. Even UT1 is an averaged time from the observations of a number of observatories, whereas GMT historically was determined from the transit telescope at Greenwich.

    See http://www.ucolick.org/~sla/leapsecs/timescales.html  for the nitty gritty on time.

    Geoffrey Kolbe
       
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