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    Re: Modern Lunars
    From: Paul Hirose
    Date: 2016 Sep 23, 16:47 -0700

    On 2016-09-20 7:43, Antoine Couëtte wrote:
    > One thing puzzles me ... the difference between our Azimuts:
    > For the Moon, you get  85.4227° , while I get: *Moon Z = 85.42280° including 
    a Parallax in Azimut equal to dZ = -14.59022” , which - without the parralax 
    in Azumuth - would put the Moon at 85.4268 °*
    > For the Sun, you get 85.4223°, while I get: *Sun Z = 85.42227°, including a 
    parallax in Azimut equal to dZ = - 0.02538”*
    
    This table shows the residuals (me - Antoine) in azimuth, altitude, and
    lunar distance.
    
    Moon az     alt    Sun az    alt    distance
    
    -0.0001° -0.0001° +0.0000° +0.0012° -0.0009° #2 sea level
    -0.0001° -0.0001° +0.0000° +0.0012° -0.0009° #2 400 meters
    
    -0.0003° -0.0001° -0.0001° +0.0002° -0.0002° #3 sea level
    -0.0003° -0.0001° -0.0001° +0.0001° -0.0002° #3 400 meters
    
    +1.0001° -0.0002° -0.0004° +0.0001° -0.0002° #4 sea level
    +1.0001° -0.0002° -0.0004° +0.0001° -0.0002° #4 400 meters
    
    I think these are mainly due to roundoff error and small differences in
    the refraction models, especially in #2 where the Sun is very low.
    
    The exceptions are the Moon azimuths in #3 and Sun azimuths in #4. I
    think they're too large to be to be easily explained.
    
    JPL HORIZONS agrees with my azimuths and unrefracted altitudes in #3 and
    #4 within 0.0001°. But note that its delta T is 7.477317, not the 7.68
    in Antoine's document. (The Astronomical Almanac says 7.6 at 1855.0 and
    7.7 at 1856.0.)
    
    HORIZONS delta T is .203 s less than Antoine, so it thinks Earth has
    rotated further east. To get compatible azimuth and altitude you must
    move the observer west to compensate. Convert .203 s to arc and get a
    longitude correction of 0.00085° west.
    
    I think the +1.0001° Moon azimuth residual in #4 is due to a typo in
    Antoine's document.
    
    

       
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