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    Compute suns position
    From: J Cora
    Date: 2006 Apr 4, 22:44 -0700
    Without much experience with a sextant but an interest in the mathematics,
    I found this web site some time ago and am just getting around to working through
    the tutorial "Computing planetary positions - a tutorial with worked examples"
    http://stjarnhimlen.se/comp/ppcomp.html

    I am part way through the tutorial and have worked up a python program for the
    Suns  RA and declination.   To verify the program and examine the results of the computation, I am using various programs such as winephem, xephem and the
    online ephemeris at ephermis.com  which I am assuming is an accurate reference.

    http://www.geocities.com/tmarkjames/WinEphem.html
    http://www.clearskyinstitute.com/xephem/
    http://www.ephemeris.com/

    The listed values for RA and dec vary among the various programs by as much
    as 5 minutes of arc, which seems to be the average change over a 24 hour day.

    The computations from the tutorial aim for an accuracy of 1 minute or less as
    compared to the values in the astronomical almanac. I have not gotten to the
    equations for GHA or LHA yet but hope to include that soon.

    Here is my question to the list, Although these simplified equations can be used
    to predict the position of the sun or other bodies, at what level of accuracy  does
    the exercise become useless?  As an example If I were off by a day the RA
    would be off by approx 5 minutes assuming the times were the same.  Please
    correct my guess here but if a 4 sec error corresponds to 1 nautical mile
    then 5 minutes represents about 60 miles of error?






       
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