NavList:

DaveP, you note that 'we need worry too much about a line through The Pointers not being exactly vertical.'

For latitude based on that star's altitude, I agree, and for exactly the reasons you gave. But it's critical for longitude. If the line through the Pointers happened to be nearly vertical, then this would place the pair on the lower branch of the meridian. This would give longitude within a couple of degrees.

Speaking of vertical, have any of you who have worked this problem dealt with the tilt of the horizon in Trammell H.'s photo? It's not much, maybe a degree or two, but if you're trying to decide on longitude based on vertical alignment of stars, the tilt of the horizon, in a north-facing photo like this, would feed right into an error in the longitude one for one, a degree of longitude error for a degree of uncorrected horizon tilt.

By my reckoning, the stars h and Θ UMa (Flamsteed numbers 23 and 25 Ursa Major) are aligned vertically and also aligned on the same line of RA which means they're the ones on the observer's meridian.

L.A.M.