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    Re: Time of meridian passage accuracy
    From: Antoine Cou�tte
    Date: 2009 Sep 26, 00:14 -0700

    COMPLEMENT TO POST 9938
    
    
    ... last part of my post # 9938 has partially disappeared, must be an error from my side !
    
    Here it is, as it gives better view of the full picture :
    
    What are the practical implications on position accuracy if and when Meridian 
    transit time not equal to Culmination time ?
    
    If the vessel has a significant north/south speed component, such as in the 
    extreme case listed here-above, then :
    
    Body declination may have changed by up to 1/15 arc minute during that time 
    period, so it is (almost) negligible for conventional Celnav, and
    
    Vessel's latitude will have changed by 0.2 ' during that time period. You may 
    start wanting to take it in account.
    
    The story does not end here however !
    
    BUT ... IF you decide to derive ship's longitude from the time of meridian 
    transit (deduced from observation of the culmination time), THEN a 25 second 
    difference between both events (Transit time and Culmination time) has 
    definitive practical implications on your longitude position. You SHOULD take 
    this effect in consideration since in 25 seconds of elapsed time, the Body 
    will have travelled some 6 arcminutes on a meridian. Therefore if you make 
    the assumption that Transit Time equals culmination time, then in extreme 
    cases, you might get a Observed Longitude in error by up to 6 arc minutes.
    
    
    Best Regards to all,
    
    
    Antoine
    
    
    Antoine M."Kermit" Couette
    
    
    
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