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    Re: Beginner Meridian Passage Question
    From: Jim Thompson
    Date: 2004 Sep 2, 09:21 -0300

    Bill,
    
    I found that the key for me was to spend time learning the coordinate
    systems carefully, early on in my training.  I still keep going back to the
    basic definitions and diagrams to remind myself of the terminology and
    relationships.  You might find these images and explanations helpful, maybe:
    
    Bowditch's glossary always keeps me on track:
    http://www.i-DEADLINK-com/bowditch/
    http://pollux.nss.nima.mil/pubs/pubs_j_apn_sections.html?rid=187
    www.marineplanner.com/bowditch/bowditch.cfm
    
    Upper branch. That half of a meridian or celestial meridian from pole to
    pole which passes through a place or its zenith.
    Lower branch. The half of a meridian or celestial meridian from pole to pole
    which passes through the antipode or nadir of a place.
    See Bowditch Figure 1524a.
    You can see a body crossing the lower branch of your meridian from your
    position in certain situations.
    (I have a hunch that the terms "upper" and "lower" come from class-conscious
    European culutures pre-1900, when everybody on the same side of something
    was "upper" crust, and all the rest were "lower"?)
    
    Coordinate Systems in CN:
    http://jimthompson.net/boating/CelestialNav/CelestNotes/Coordinates.htm
    (in particular the section on the Navigational Triangle near the bottom,
    where there are a couple of diagrams for meridian crossings of the upper and
    lower branches.)
    
    Meridian Transit sight reduction:
    http://jimthompson.net/boating/CelestialNav/CelestNotes/SightReduction.htm#M
    eridianTransit
    
    Noon Sun:
    http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm
    
    Jim Thompson
    jim2{at}jimthompson.net
    www.jimthompson.net
    Outgoing mail scanned by Norton Antivirus
    -----------------------------------------
    
    
    

       
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