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    Lunars for dummies like me
    From: Jim Thompson
    Date: 2004 Sep 23, 11:36 -0300

    I am still crawling up the lunar distance learning curve.
    
    I understand most of the issues around how navigators estimated their
    longitude using GMT from a lunar distance sight, and latitude from a noon
    sun sight.  But I am stupidly stuck on step 5.  Did navigators of the day
    set a ship's clock to GAT obtained from the lunar distance, and then
    therefore know the difference in time between when they took their lunar
    observation of GAT, and when they took their morning or afternoon time sight
    of the sun?  Or did they do this without any ship's timepiece at all?
    
    For example, is this correct?:
    
    1. Navigator took a lunar distance observation on the evening of day 1,
    yielding GAT for that point in time and space.
    2. Navigator continued careful dead reckoning.
    3. Navigator determined latitude at LAN from a noon sun sight on day 2.
    4. Navigator took a time sight of the sun late in the afternoon of day 2,
    when the sun was nearly due west, yielding LHA of the sun based on careful
    dead reckoning for latitude, and therefore obtained LAT.
    5. Navigator advanced his estimate of GAT from the lunar sight to the
    afternoon sight, using a local timepiece set to GAT at the time of the lunar
    sight the day before, and then determined longtiude using the formula GAT =
    LAT +WLo or -ELo.
    
    Based on Frank Reed's article on easy lunars, I am working out a
    step-by-step form for recording and clearing lunar distances:
    http://jimthompson.net/boating/CelestialNav/CelestNotes/LunarDistanceFormJT.
    htm
    
    I have collected the lunar distance links at
    http://jimthompson.net/boating/CelestialNav/LunarDistances.htm
    
    Jim Thompson
    jim2{at}jimthompson.net
    www.jimthompson.net
    Outgoing mail scanned by Norton Antivirus
    -----------------------------------------
    
    
    

       
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