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    Re: How good were chronometers?
    From: Greg B
    Date: 2006 Mar 15, 10:38 -0500

    Frank in a archived post I found this working of a time sight:
    
    Almanac data:
            GHA Sun: 171d 27.4'
            Dec Sun: 1d 17.6' S
            EqT: + 8m 38s
            GMT: 23-17-12
            GAT: 23-25-50
    
    Method 1: Direct Computation
    
            Lat = L = 48.50167
            Dec = d = -1.27833
            Ho = h = 24.90500
    
    cos t = (sin h - sin L sin d) / (cos L cos d)
    cos t = 0.66093
        t = 48.62894
        t = 48d 37.7'
    
    For an afternoon sight,
        Lon = GHA - t
            = 171d 24.4' - 48d 37.7'
            = 122d 49.7'
    
    OK, a couple of questions:
       (1) I thought you had to use co-latitude , co-declination, &  co-Ho? (If
    this was already done I must have missed it).
       (2) This looks suspiciously like every other spherical / navigational
    triangle so why do you say stars were not used except for lunars?
       (3) Are you saying you can't get a good longitude from just the noon
    site?
    My reason for asking is that I do a lot of rev-war & pre-1840 re-enacting
    and I'm trying to understand exactly what was done
    on land & sea. I know for example that on land both David Thompson & Lewis
    & Clark took Lat via Polaris.
    
                                                                   -Greg
    
    
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