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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2021 Oct 13, 07:40 -0700
Dear Lars,
Thank you for your reply.
Obviously we get the same results.
With "R" being the Earth Radius, "a" the Observer's altitude, "α" the A/C elevation above the true horizon, then the slant range "s" from A/C is given by the full formula as:
s / (R+a) = -sinα + sqrt { sin²α + [ (h-a)/(R+a)] * [2+[(h-a)/(R+a)] ] } (see one of the enclosures)
Hence with R = 6,378,137 m, a = 0 m : For α = 0.78° get s = 176.4 NM and α = 0.78° - (19/60)° = 0.466666...° get s = 192.2 NM.
Frank, you mentioned this site. If using their exact R value, i.e. 6,371,009 m, then I am deriving exactly the same values as they are publishing for all and any configuration.
And finally, for all, from a second enclosure, you will see how I accurately measured my "local horizon". T'was fun in that windy day.
Antoine M. "Kermit" Couëtte
antoine.m.couette[at]club-internet.fr
