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    "Time Sights" and Lines of Position
    From: Doug MacPherson
    Date: 2016 May 15, 11:54 -0700

    I learned the "logarhythm" method of computing a "time sight" from a 1938 copy of Bowditch.  The chapter on "time sights" shows you how to compute your Longitude based on a DR Latitude, but does not show you how to obtain a Line of Position.  

    As has been pointed out by Frank and others in previous posts, a LOP can be easily obtained from the "time sight" information at hand by computing the Azimuth.  I like to use the ABC tables in my 1991 copy of Norie's which requires LHA, Latitude and Declination as inputs.  You can certainly use logarhythms as well for the computation using the equation [SinZ=sin(t) cos(d) sec (h)].

    My question concerns the 19th century practices.  Did those navigators commonly obtain an LOP after the "time sight" calculation by computing an azimuth?  Or was this pretty unheard of?  if not a pracitice, was this because they prefered  to keep their charts free from LOP lines, or had they never been introduced to the LOP possibility?  Other reasons?



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