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    Re: Basics of computing sunrise/sunset
    From: Christian Scheele
    Date: 2009 Jun 19, 20:14 +0200

    Many thanks, Frank, for the clarifying words on the limits of computing
    sunrise/set times. Being a function of athmospheric conditions at any
    possible point on earth, refraction values, I admit, remain estimates,
    however good. But in theory: Assume you know the athmospheric conditions to
    "the  horizon" and beyond right up to GP of the sun, i.e. you are able to
    monitor these conditions for this entire stretch; say you have an imaginary
    string of weather balloons thousands of miles long. Would that solve
    refraction? Then other problems remaining would include anomalies in the
    curvature of the earth's surface, errors in the observer's height and
    sextant errors.
    "The same calculation is used for inland locations as for locations with a
    sea horizon."
    Sunset yesterday from my raised point of observation, the horizon being at
    sea level, was 3 minutes later than the time calculated for an observer at
    seal level.
    Christian Scheele
    Navigation List archive: www.fer3.com/arc
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