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    Home brewed lunar distances
    From: Herbert Prinz
    Date: 2004 Apr 5, 02:18 -0400

    Frank Reed wrote:
    
    > Predicting lunars is every bit as easy as calculating altitudes.
    > Having pre-calculated distances in an almanac saves maybe five minutes
    > of table work, but that's all.
    
    Come on, Frank, aren't you exaggerating here just a tiny bit?
    
    The problem of  generating the lunar distance is identical to the great
    circle sailing problem. Those of us who work with Pub. No. 229 can have
    a look at pp. xx - xxii to see what is involved.
    
    Your typical sight reduction table is ill suited to solve distances > 90
    deg, creating cases and headaches. It is designed to work for integer
    values of LHA only, creating the need for either double entry numerical
    interpolation, or graphical interpolation. If you want 0.3' accuracy, I
    recommend patience and a sharp pencil.
    
    And you need to solve two of these triangles, allowing you 150 seconds
    for each.
    
    Also, the Almanac data is not really meant to be used in this way. The
    GHA sun is adjusted to work with the interpolation table in the back of
    the almanac without a v-correction. (Frankly, I don't see why they are
    doing this.) Maximum deviation is 0.15' of arc. Not much, but it all
    adds up.
    
    I had a quick look at Letcher. He works with the Dreisonstok tables,
    with the details of which I am not familiar. But I see that it also
    requires a graphical solution. Can't imagine that it makes all that much
    of a difference?
    
    Best regards
    
    Herbert Prinz
    
    
    

       
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