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    Extra-terrestial celestial navigation
    From: Peter Fogg
    Date: 2003 Feb 14, 10:08 +1100

    Peter Fogg wrote:
    
    >
    > While in earth orbit I had imagined that Declination and Sidereal Hour Angle 
    and Distance from Earth could form the 3 axis for a 3 dimensional fix. But 
    what are the references
    > once you leave the earth behind? I guess the star field remains a (relative) 
    constant, reference to the earth or the sun would be confusing because of 
    their movement?
    
    After thinking about this some more it has become clearer, at least in my own mind (funny about that).
    While in earth orbit simple latitude and longitude coupled with altitude is 
    all that is needed. The problem with celestial navigation away from the earth 
    is that the celestial
    sphere is predicated with the earth at its centre. And the problem with that 
    is that the earth is spinning on its axis and also orbiting the sun. But a 
    slight shift in
    definition, to taking the sun as the centre (strictly speaking, the centre of 
    the sun) doesn't make much difference to the celestial sphere (as we 
    understand it) and gives a
    (relatively) static object as a reference point. So I guess the new equator is 
    the plane on which the planets revolve.
    
    So: Dec and SHA remain usable (for lack of an alternative we are still using 
    the first point of Aries as our longitudional reference point) and distance 
    from the sun becomes the
    3rd axis. Hhm, I think we still need a north south east west equivilant to 
    designate in which quadrant of the orbital plane we are located. Back to the 
    drawing board. In any
    case, this system is only useful so long as we remain within our own solar system.
    
    Of course, whether the actual method(s) used are similar to this I have no idea.
    
    
    

       
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