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    Re: My first Lunar
    From: Frank Reed
    Date: 2008 Sep 22, 23:41 -0400

    George, you wrote down the inputs for the analysis :
    "DR Lat 14�  31'  N
    DR Lon 61� 38.1' W
    Body - Jupiter
    January 26 1999
    22 19 30 GMT
    Distance 68� 19.4'  near." 
    
    But you've dropped the measured altitudes. We can talk about the procedures 
    and issues when no altitudes are measured, but that wasn't the case here. 
    Enter the altitudes as measured. Those, combined with the observed apparent 
    lunar distance, imply one and only one geocentric lunar distance and 
    therefore one specific value of GMT. So you do that part first: adjust GMT 
    until the error in the lunar is exactly zero. From then on, you assume GMT 
    is FIXED. The calculator also gives you the "error" in the observed 
    altitudes assuming you're at that DR position at the entered GMT. So next 
    you just chase down that location (actually two) where the error in the 
    altitudes goes to zero (this is an ordinary position fix from two altitudes 
    at known GMT). And when you're done, you have GMT, longitude, and latitude, 
    too. From there, you can do things like test for the sensitivity to error in 
    the three observed angles. 
    
    Needless to say, there are many variations in the way you could deal with 
    this lunar observation You could look at it from a more historical point of 
    view thinking in terms of an actual time sight calculation. You could ignore 
    the measured altitudes, and think about the issues when altitudes are 
    calculated. Or you could think about the sight as a somewhat later but still 
    historical check on GMT directly. Or you could look at it as a modern sight 
    at KNOWN Greenwhich Time and use the measured lunar distance to generate a 
    "lunar distance line of position". So many options; so little time... 
    
    Happy to discuss this more. I don't have a lot of time for this post today, 
    and I've been very busy recently, so I'm trying to keep it short for now. 
    
     -FER 
    
    
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