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    Re: CP-300/U Star Finder
    From: Paul Hirose
    Date: 2015 Mar 10, 22:09 -0700

    On 2015-03-09 10:01, Russ Keller wrote:
    > Are these limited to a particular span of years.  Or in other words are 
    these still useful for sight planning?
    
    Yes, they still work. The precession of the celestial equator causes a
    constant movement of the SHA/dec coordinate system. However, this
    amounts to only one degree (in great circle measure) every 72 years for
    a star on the ecliptic, less elsewhere.
    
    Even if the coordinate system maintains a fixed orientation, the space
    motion of the stars with respect to our solar system gives them slowly
    changing coordinates. That's called "proper motion". At 3.7 arc seconds
    per year, Rigil Kentaurus has the greatest proper motion of the
    navigational stars. But that's almost 1000 years per degree, so the
    effect on a star finder is negligible compared to precession.
    
    

       
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