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    Re: H. Hughes and son sextant pat 491
    From: David Pike
    Date: 2019 Dec 4, 01:24 -0800

    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 PZX­1 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

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