NavList:

Hi David,

Yes, you nailed it - the problem is the 2-dimensional view that I, as an observer, see, mapped against the 3-dimensionsal celestial sphere. I have been fooling with Napier's rules, but am just getting my toes in. I am sure this has been done by Weems or somebody, but I do find the spherical trig interesting to learn and work out. You have shot in the yellow points, at altitude 'al' (with the fixed-angle Briss sextant) and (half) the time difference gives you angle 'A'. Since you have 'r', the goal is to get 'b' and therefore 'd'. Once you have 'd', you add to 'al' to get your altitude at local noon. The underlying image is from Stellarium with the daylight removed and the equatorial grid on. The yellow lines are in the plane of view, and the red are on the celestial sphere.

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