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    Re: Precomputed lunar distances
    From: Fred Hebard
    Date: 2005 Apr 10, 21:16 -0400

    On Apr 10, 2005, at 7:32 PM, c roberts wrote:
    
    > In postings on this list , altitudes and azimuths were required for
    > accurate calculations of distances between bodies. How can
    > precomputed lunar distances be done as has been done for centuries??
    > It would seem that almanac GHA and DEC are the only data available.
    > This same calculation would be used for inter stellar distances for
    > checking sextant calibrations. It has been said that the values in
    > Bauer's book are wrong. In the lunar distance calculations this value
    > which is used to proportion for GMT is calculated. Can precomputed
    > values be used to avoid this ?
    >
    > Searching for the best free email?  Try MetaCrawler Mail, from the #1
    > metasearch service on the Web, http://www.metacrawler.com
    
    GHA and DEC are used to precompute lunar distances or other distances
    between bodies.  Altitudes and azimuths don't enter into the
    calculation.  Computation of distances on the hour for interpolation to
    minutes and seconds is still a component of methods of determining GMT
    from lunars.  The distance computations can be done beforehand,
    precomputed, or as part of the process of clearing a set of lunar
    distance observations.
    
    Refraction is critical to clearing both interstellar and lunar
    distances.  The mistake Bauer made in the table in his book is that he
    did not account for refraction.  That, of course, would not be possible
    without knowing one's position.
    
    Refraction is dependent upon altitude, and altitudes either have to be
    computed or measured to determine refraction when clearing lunars or
    interstellar distances
    
    George Huxtable gave a method suitable for electronic calculator using
    "Young's Method."  Frank Reed gave one of the "approximate" methods.  I
    believe both these methods are linked or presented on Arthur Pearson's
    website
    .
    
    Fred
    
    
    

       
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