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    Re: Dip: Astronomical Almanac vs. Nautical Almanac
    From: Brad Morris
    Date: 2013 Apr 21, 21:29 -0400

    Hi Marcel

    I don't think there is an appreciable difference.  For either reference, dip is 1.75sqrt(H,m) or  1.76sqrt(H,m).  The only difference in dip equation is 0.01sqrt(H,m).

    If you want the rise (or set) refraction of an celestial body (NOT DIP) on that horizon, then the additional refraction of that body is .37sqrt(H,m). 

    I think perhaps you have misinterpreted the section.

    I believe its saying that celestial body must be lower in altitude than vacuum geometry would predict, to make that body appear on the horizon, as a function of height of eye.  The light from the body is raised by refraction before it arrives at the horizon.  Therefore, for it to be coincident with the horizon, the altitude of the body must be lower.  Lower by an additional .37sqrt(H,m).  This is only for the celestial object, NOT for the horizon.

    Hopefully, I have explained this properly. 


    On Apr 21, 2013 8:17 PM, "Marcel Tschudin" <marcel.e.tschudin@gmail.com> wrote:

    Hi Brad,
    Yes we discussed this very recently on the basis (at least on my side)
    of the Nautical Almanac. It appears to me that there is a noticeable
    difference between the two Almanacs. If my interpretation would be
    correct then the dip would differ between the two Almanacs by
    Diff[moa]=0.36[moa]*sqrt(H[m]). I am just wondering whether this
    difference is "real" or only resulting from some misinterpretation.
    According to my understanding the equation which you indicate should
    have brackets and read A  - [ D(H) - R(H) ], but I may have missed
    something already before.

    View and reply to this message: http://fer3.com/arc/m2.aspx?i=123640

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