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Dear Geoff,

An unfortunate computation shortcut in my previous post needs some significant correction as regards the actual unrefracted elevation of MonViso summit seen from the Observer.

(1) - With MonViso Google Map position at 44°40.05'N 007°05.5'E (Google Altitude at 3,841m) :

(1.1) - The WGS84 equatorial radius being 6,378.137 km, the actual ellipsoid radius at 44°40.05'N is 6,367.614 km

(1.2) - Therefore with its Google Altitude at 3,841m, the MonViso summit geocentric distance is 6,371.455 km

(2) - With the Photographer's Google Map Position at 45°08.7'N 007°52.5'E (Google Altitude at 455 m) :

(2.1) - The WGS84 equatorial radius being 6,378.137 km, the actual ellipsoid radius at 45°08.7'N is 6,367.435 km

(2.2) - Therefore with its Google Altitude at 455 m, the Photographer geocentric distance is 6,367.890 km   .

(3) - Since on the WGS84 Ellipsoid both Vectors are separated by (43.955/60)° = 0.73258°, then :

MonViso unrefracted summit angular elevation seen from the Observer's position is 2.13954° / 2°08.4'

(instead of previous value at 2.015° / 2°01.0' )

(4) - Meanwhile, I have searched about documents dealing with refraction affecting summits seen from the ground. In this site in particular, for a mountain seen at the horizon (horizon grazing Mount Canigou seen from Marseilles at a distance of over 263 km), they observe that actual refraction is only 1/4 of the total atmospheric refraction.

Instead of the previous 1/2 total inverse refraction at 10' (which actually would now put MonViso summit above LadyMoon Upper Limb, hiding at least its this UL), if we take 1/4 of total inverse refraction - i.e. 5' - then we end up with a refracted MonViso summit at 2°13', i.e. exactly where it shows on the Picture.

Hope everything is adequately covered now.

Kermit