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    Re: Zenith Fixes
    From: Jeremy C
    Date: 2019 Mar 26, 06:13 -0700


    This is based on a sight I posted 11 years ago (where has time gone!?), and sailors call these "high altitude sights."  The two or three observations are taken and advanced to 1200 in order to get the traditional noon fix, which in turn is used to calculate the day's run.  We wouldn't consider it a DR, even though it is, but more like a running fix where LOP's are brought to a singular time.  We also do this with stars.  For example, if I shoot all of my stars between 1815 and 1825, I would likely advance them all to 1830 for a nice even fix time.  As you point out, this wouldn't be useful for air navigation.

    Traditional methodology with high altitude sights is to plot the GP's of the body and adjust them using the course and speed to the common time.  Then you would draw arcs whose radius is based on the minutes of zenith distance for each observatio,n and where they intersect, you have a fix.  3 observations should eliminate the ambiguity inherent in 2 observations.


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