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    Re: Delta-T
    From: Omar Reis
    Date: 2004 Dec 6, 12:01 -0200

    >George Huxtable wrote:
    > This has table 10A giving delta-T for various years from 1620, for which
    he
    > quotes +121 sec, to 1998. Unfortunately, this table says nothing about the
    > errors involved. Meeus' Table 10A differs significantly (for dates around
    > 1620) from the numbers given in my 1984 Astronomical Almanac, which gives
    > +98 sec for 1621. Meeus states that the Astronomical Almanac values have
    > been "corrected" according to a new value for tidal acceleration of the
    > Moon, given in note S055, issued by the Bureau des Longitudes, Paris, in
    > 1997, by Chapront et al. The tables agree, for more recent dates.
    >
    > Meeus (1998) also gives equation 10.2 giving delta-T "from +948 to + 1600,
    > and after the year +2000". in seconds, as-
    > 102 + 102 t + 25.3 t-squared,  (Meeus eq 10.2, on page 78)
    >
    > where t is the time in centuries from year 2000, so for 1600, t = -4.0
    >
    > This is quite different from the expression Omar quoted, as
    >  "DeltaT=50.6+T*(67.5+T*22.5)      (T in centuries since J2000) "
    > se perhaps we have different editions. Has that equation 10.2 (1998) been
    > subsequently revised in a later edition of Meeus? Otherwise, where did
    Omar
    > get it from?.
    
    I have the first edition (1991), to which I have applied the "errata" by
    the author (1995). The formula is to be used between years 948 and 1620
    I was calcuting  dT for 1580, so I used it.
    
    Omar
    
    
    

       
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