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    Lunar Distance Details
    From: Dan Allen
    Date: 1998 Jun 09, 1:55 PM

    Here's a bit more detail about taking lunars, so you can see that the
    calculations are maybe three times what the calculations are for a standard
    sextant fix:
    
    Lunar Distances
    ---------------
    1. Measure angle between Moon and the Sun or a star near the ecliptic.
       Correct for semi-diameter and any instrument error.
    2. Call this Do.
    3. The altitude of each body is observed simultaneously or adjusted to the
    same time.
    4. The equivalent geocentric distance Dog is then:
    
                                   (cos(Do)-sin(ham)*sin(has))*cos(Hom)*cos(Hos)
    cos(Dog) = sin(Hom)*sin(Hos) + ---------------------------------------------
                                                cos(ham) * cos(has)
    
    where
    
    Ha  = apparent altitude (sextant altitude corrected for dip and index error)
    Ho  = observed altitude (apparent altitude corrected for refraction,
    semi-diameter, parallax)
    sub m  = moon
    sub s  = sun or star
    
    5. The calculated value of the lunar distance Dc is:
    
       cos(Dc) = sin(dm) * sin(ds) + cos(dm) * cos(ds) * cos(SHAm - SHAs)
    
    where
    
    d is declination,
    SHA is siderial hour angle,
    and the subscripts m and s denote moon and sun.
    
    6. The Dc should be calculated for a time believed to be earlier than the
    correct time, and again for a later time.  The Dog and the two values of Dc
    are compared and the correct time determined by interpolation or
    extrapolation.
    
    (From Navigation Afloat, Alton B. Moody, New York: Van Nostrand, 1980, page
    629.)
    
    Daniel K. Allen == Windows CE Tools & VMs Test Manager ==
    danallen{at}microsoft.com
    Sent from N47�38.592' W122�07.309' == Building 32S/2123, Redmond, WA
    Measure, Analyze, Communicate
    
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