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    Re: Long and Time at Sea
    From: Lu Abel
    Date: 2005 Jun 4, 13:56 -0700

    Gordon Talge wrote:
    > The "Noon Sun Shot" was a staple. However, due to the fact that the
    > Sun tends to "hang" in the sky on the meridian with little apparent
    > change in altitude means that finding longitude by noting the time
    > of passage, while in theory should work, in reality is not practical.
    >
    > One method has the observer, taking a shot at maybe 10 minutes before
    > LAN and noting the altitude and the watch time, doing a noon shot
    > and resetting the sextant to the altitude that was noted 10 minutes
    > before and watching the Sun until it is at this same altitude and
    > noting the watch time. Since the Sun must have been at LAN midway
    > between these two times, you then calculate that time and using the
    > equation of time from the NA get your longitude.
    
    I don't know how many on this list have actually taken a noon sight.  I
    have.
    
    A noon sight is part of the requirements for US Power Squadron's
    Navigation course (advanced celestial nav) which I have taken.  I found
    (at ~40N Lat, sight taken during the early summer) that not only did I
    get a spot-on latitude value, but by graphing a series of sights over
    about 10 minutes (5 min on either side of LAN) I got quite an excellent
    value for longitude.
    
    The sun being "nearly stationary" in the sky is relative.  For an early
    navigator using a backstaff and lucky to get latitude to 1 degree, the
    sun truly appeared to be hanging in the sky at LAN.  But looking at it
    through a modern sextant, I found the vertical movement around LAN quite
    perceptible.   I also freely confess this sight was taken on dry land,
    so I wasn't dealing with trying to bring down the sun on a heaving
    ship's deck.
    
    Lu Abel
    
    
    

       
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