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    Re: Basics of computing sunrise/sunset
    From: Christian Scheele
    Date: 2009 Jun 28, 16:41 +0200

    referring to my "weather balloon" posting, you said : "Despite answers from
    Frank et
    al, they seem like overkill to me."
    Frank's reply began with the words, " Oh yes, I agree with that", but here I
    don't think he had my - admittedly spur-of-the-moment - idea of a line of
    sight from the observer to the GP of the sun in mind, as you suggest.
    Rather, he affirmed and elaborated on the effect of changing athmospheric
    conditions on refraction.
    Christian Scheele
    ----- Original Message -----
    From: "Bill" 
    Sent: Saturday, June 27, 2009 8:49 AM
    Subject: [NavList 8844] Re: Basics of computing sunrise/sunset
    >> From: "Christian Scheele"
    >> 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.
    > This series of weather balloons to the GP of the Sun setting on my horizon
    > caught my interest, but I have not had the time (or mental horsepower) to
    > give it the necessary thought to follow up. Despite answers from Frank et
    > al, they seem like overkill to me.
    > My questions. If I recall the GP would be approximately 5400 nautical
    > miles
    > (nm) away when I see Sun set (using appropriate eye protection of course).
    > In my mental picture, I am not wrapping my vision along the surface of the
    > Earth. I have a line of sight from my eye position to the Sun, which will
    > run out of atmosphere *long* before 5400 nm or the 93 million miles to the
    > Sun.  Therefore I would want a series of hypothetical weather balloons
    > along
    > my line of site.  But would that help with thermal inversion/abnormal
    > lapse
    > rates causing refraction anomalies at my visible horizon?  Do I need a
    > series of balloons up from my horizon?
    > Any help in clearing up my confusion would be appreciated.
    > Bill B.
    > >
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