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    Accuracy of ephemeris
    From: Bill Lionheart
    Date: 2017 Oct 16, 09:21 +0100

    I have been using the python ephem package for ephemeris and it is
    based on code from Xephem, with a discussion of accuracy here
    http://www.clearskyinstitute.com/xephem/
    
    I have seen other discussions of accuracy of ephemeris software on
    NavList and I am sorry if this has been covered before
    
    1) Where can I find an analysis of the effect of errors on the
    intercept  method? Hence the answer to the question "How accurate does
    ephemeris need to be for celestial navigation?" . I know we are
    limited by time and angular resolution in taking sights but we can
    average over a series of sights to reduce this error, but after errors
    in reading the sextant and chronometer is the next biggest error going
    to be variations in the atmosphere? Suppose we are using celestial
    navigation at a fixed point on land and we can average over different
    atmospheric conditions.
    
    2) Is there a "gold standard" ephemeris used in astronomy? It strikes
    me in meteorology the gold standard must be to check predictions with
    observations. Presumably there are observatories making high precision
    measurements with minimal errors (for example when objects are near
    the zenith to reduce refractions).
    
    --
    Professor of Applied Mathematics
    University of Manchester
    http://www.maths.manchester.ac.uk/bl
    

       
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