Re: HP-41 Navigation PAC question Message #2 Posted by Dave Shaffer (Arizona) on 22 Feb 2012, 12:11 p.m., in response to message #1 by Diego Diaz
Not really a sailor, but an astronomer!
Due to the precession of the Earth, the apparent position of stars in the sky with respect to the Earth-based lat/lon system changes slowly and systematically as the years go by. The annual change is around 1 arcminute per year - comparable to the accuracy that a really good sextant user might hope to achieve.
So, if you are worried about running aground at the nautical mile level, you do need current star positions.
I have no idea - does the Nav Pac apply precession? If it does, it should more-or-less stay up to date for quite a while.
There is also proper motion of stars (they move around in space), but this is at the arcsecond per year level (generally, much less) so you shouldn't have to worry about this for a century or more!
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