A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2013 Apr 21, 21:29 -0400
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.
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. Marcel
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