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    Re: Low Alt Refraction
    From: Antoine Couëtte
    Date: 2013 Apr 29, 06:23 -0700

    Hello Paul and Marcel,

    This Post in reply to your last 2 posts :


    To you Paul,

    RE : http://fer3.com/arc/m2.aspx/Low-Alt-Refraction-Hirose-apr-2013-g23719

    Thanks for specifying a Formula published in the "new" Explanatory Supplement (ES). It shows up as Formula (3.282-2) in the ES 1992 Edition.

    Your remark prompted me into closer searching the "older" (Sep 1977) ES version for any actual information on Refraction at 0° apparent height. Apart from the Standard -34' value used for the SUN and MOON risings and settings, the only additional information in Section 2E is a reference to Chauvenet's "Manual of spherical and practical astronomy" (1960 reprint) and another reference to Smart's "Text-Book on Spherical Astronomy" (1944 reprint).

    In Smarts's Sixth Edition (1977 / 1980 reprint) : again ... apart from the standard -34' refraction value, I fail to see any more specific mention to any Low Altitudes Refraction Values.


    RE : http://fer3.com/arc/m2.aspx/Low-Alt-Refraction-Tschudin-apr-2013-g23724

    Hello Marcel,

    First of all, sorry for a few typos which I had mistakenly printed in my post RE : http://fer3.com/arc/m2.aspx/Low-Alt-Refraction-USCG-Student-Example-for-Low-Altitude-Couëtte-apr-2013-g23718

    Please find here-after a few comments where applicable.


    Reference #3: The air pressure is given. I do not know what the water
    pressure relates to.


    REPLY : It means "Water Vapor pressure", i.e. Humidity 0%, or Air entirely dry.



    Reference #6: Could this have been a typo and the value been in
    degrees, still requiring to add the sun diameter?


    REPLY : This is a typo . Sorry again. This value actually reads - 34.0' which is most probably a simple copy/paste of the Standard -34' value used in the US/UK N.A.'s for SUN/MOON risings/settings.



    References #10 and #11: It looks like being the same formula. There
    seems however to be a slight difference. Was #11 not copied correctly?
    (I do not have the original reference.)


    I do not hold a copy of such original formula either ...


    Best Regards to both of you

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