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    Re: Modern Lunars
    From: Paul Hirose
    Date: 2016 Sep 27, 00:46 -0700

    On 2016-09-25 22:08, Antoine Couëtte wrote:
    > Also are my Apparent Equatorial Coordinates from the Bureau des Longitudes 
    Server the same as the ones you are obtaining on your side ? Maybe this 
    should be the very first point to check again together this time. I am using 
    the following ones (*before* performing the +0.50"/-0.25" correction earlier 
    mentioned):
    > *Moon, 1855-09-07T08:05:00.00, i.e. 08h05m00.000 s TT : RA = 08 h 10 m 
    10.16146 s , DEC = +25 *°* 17 ' 31.0209 ", Distance = 0.002701090 UA,*
    
    My problem with the IAU 1976/80 precession / nutation model has been fixed.
    
    08 10 10.16146 +25 17 31.0209  ---  Bureau des Longitudes
    08 10 10.1690  +25 17 31.006   .10  JPL HORIZONS
    08 10 10.165   +25 17 31.01    .14  me DE406 1976/80
    08 10 10.196   +25 17 30.96   1.31  me DE406 2006/00B
    08 10 10.195   +25 17 30.97   1.27  me DE422 2006/00B
    
    The error column is the separation angle (arc seconds) with respect to
    the Bureau des Longitudes position.
    
    Apparently the Bureau des Longitudes still uses the IAU 1976/80
    precession nutation model. JPL does too, but it's corrected with the
    pole offsets (from the IERS) in recent epochs. I don't know what
    corrections they apply in the 19th century.
    
    I used my lunar program (IAU 2006/00A precession nutation model) to
    calculate the 4th and 5th lines. However, in the 3rd line I used a
    different program to calculate the Moon's geocentric apparent place with
    IAU 1976 precession and 1980 nutation. It agrees closely with the BdL
    and JPL positions.
    
    I think the position discrepancies are almost entirely due to different
    precession / nutation models. It's unfortunate that two gold standards,
    the BdL and JPL, continue to use IAU 1976 precession, which was known to
    have accuracy problems by the 1990s. The IAU 2000 model was basically a
    simple rate correction to the 1976 model. In the 2006 model (the current
    one) we got something completely new and much better. It's even fairly
    good for archeoastronomy.
    
    My lunar program says 7h08m13.903s Greenwich apparent sidereal time,
    within a millisecond of Kermit.
    
    

       
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