NavList:

Frank Reed you wrote: For example, he repeats a common myth that was prevalent among navigators in the US Navy, especially, in the 80s and 90s (probably earlier, too). He states: "star pairs in the horizontal plane give more accurate results because when altitudes are about the same refraction can be ignored." This is completely false.

I’m familiar with the expression ‘neat, plausible, and wrong’ but I’m struggling a bit in this case.  I can see Bauer’s explanation is neat, I can see that it’s plausible, but why exactly is it wrong.  Is it meteorological?  I.e. the atmosphere might not be the same in every direction.  Or is it geometrical?  I.e. you measure what you see and not what spherical geometry says you should see.  In other words, and in terms of PZX triangles PZX_­1 and PZX₂, as the bodies appear higher in the sky than they are, the angle between them measured with a sextant will be less than the calculated angle.  I.e. refraction reduces angles X₁Z and X₂Z by a tiny amount, so the angle X₁X₂ is also reduced. If these are the reasons, typically how inaccurate is the measurement likely to be? DaveP