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Alexandre Eremenko wrote:
> This can be easily fixed, of course, just by
> tabulating ALL mutual distances between the usual 57 navigational
stars.

Be careful -- the stars' apparent positions, even after correcting for
refraction, vary over the course of a year by several tenths of a
minute.
This is called "annual aberration" or "aberration of starlight" or
"stellar aberration", and is caused by changes in the direction of
earth's
orbital motion.  A star's apparent position shifts by an amount equal to
  arctan ( orbital_speed / speed_of_light )
toward the direction of the earth's motion.

Historical note -- this effect was first discovered by astronomers
who were trying to measure parallax of stars (using the earth's orbit
as a baseline) to determine how far away they are.  It turns out that
parallax is (almost always?) a much smaller effect.

   

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