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    I need help with my first noon sun sight
    From: Jim Thompson
    Date: 2003 Dec 20, 10:26 -0400

    Please see my calculations below for 3 ways to predict the local zone time
    for meridian transit of the sun on September 14, 2003 at my position of L
    46o 11.1' N, Lo 63o 08.0' W (GPS Fix).  I cannot understand why Methods 1, 2
    and 8 produce different predictions.  Can anyone spot the reason?
    
    I made a time diagram of this problem, though I am not sure that it is
    correct, and it gives yet a third answer:
    http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm#Time%20Diagram
    (ignore the rest of what I have written on that page -- I am still muddling
    through this).
    
    Thank you,
    
    Jim Thompson
    jimt2{at}jimthompson.net
    
    ------------
    
    Method 1.  13h 08m 09s WT, using the Canadian Power and Sail Squadron's
    student notes method of working back to time starting from the sun's Almanac
    GHA next smaller than the observer's AP longitude:
    
    1. AP = Lo 63o 08.0'W.  This is equivalent to 04h 12m 32s of time.
    2. GHA = 61o 05.7' at whole hour GMT 16h.  (This is equivalent to 04h 09m
    23s of time, and is 01o 05.7' or 04m 23s past the Time Zone's central
    meridian of 60o 00.0' W, which in turn is equivalent to 04h 00m 00s past the
    Greenwich meridian.)
    3. Difference of Lo 63o 08.0'W from 61o 05.7' = 02o 02.3'.  Converting that
    difference of 02o 02.3' to time units from Increments and Corrections table
    = 08m 09s.
    4. So GMT = 16h + 08m 09s = 16h 08m 09s when the sun is at transit over Lo
    63o 08.0'W.
    5. ZD +4 (-1 for DST).
    6. ZT = 13h 08m 09s.
    
    ------------
    
    Method 2. 13h 08m 32s, using the Bowditch section 2010 method of looking up
    the time of Meridian Passage in the Almanac:
    
    1. Almanac Meridian Passage time = 11h 56m (Greenwich mean time) for
    September 14, 2003.  So meridian passage also occurs on our Time Zone's
    central meridian (60o 00.0' W) at 11h 56m Zone Time.  Arc distance (DLo) to
    our Time Zone's central meridian of 60o 00.0'W = 03o 08.0', which converts
    to a time span of 12m 32s.
    2. Add that to 1156 to get 12h 08m 32s, which should be the corrected time
    on our watches when meridian passage occurred.
    
    -----------
    
    Method 8. 13h 08m 13s by analyzing a Time Diagram:
    http://jimthompson.net/boating/CelestialNav/NoonSunSight.htm#Time%20Diagram
    
    -----------
    
    
    

       
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