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    Re: Interpolation to latitude
    From: Joe Schultz
    Date: 2009 Nov 9, 14:29 -0800

    Hi Inuik,
    "Convert each LMT to GMT  by adding... or subtracting .. the time equivalent 
    of the expected DR longitude..."
    Mean time is directly correlated to longitude.  In other words, the longitude 
    correction is a direct calculation.  I use a 4-2-1 memory aid: 4min time per 
    degree longitude, 2min time per 30min longitude, 1min time per 15min 
    For your exercise, I mentally calculate the longitude correction as:
    50d15m - 45d longitude = 5d15m longitude = 4 five times plus 1 = 20 + 1 = 21m time.
    We are west of the zone meridian of 45d so we add the longitude correction to 
    LMT to obtain the event zone time (ZT), then add another 3hr to obtain the 
    event GMT.  3hr was another mental calculation: 15, 30, 45deg longitude = 1, 
    2, 3hr time.
    It's important to remember that latitude and longitude are not coordinate 
    positions on the surface of the earth.  They are angles, measured at the 
    center of the earth.  Distance on the earth's surface is correlated to 
    latitude, and mean time is correlated to longitude.
    Interpolating for the latitude correction is a mathematical short-cut which 
    isn't exactly correct, but is close enough for us in this type of exercise.  
    Otherwise we'd spend all day just calculating the latitude correction.
    I do get the answers in your 10521 post.
    Hope this helps,
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