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    Re: Figure out LAN?
    From: Paul Hirose
    Date: 2014 Oct 01, 22:20 -0700

    On 2014-10-01 10:01, Samuel L wrote:
    > Is the following example correct in determination of LAN using GHA?
    > Date- October 1, 2014
    > Latitude- N 41d
    > Longitude- W 75d 22.4min
    > LAN= 11:51:06.39  (12:51:06.39 DST)
    
    
    Doesn't look right. GHA at that time is 75°22.1′ per the USNO celestial
    navigation calculator. At apparent noon, GHA should match your longitude.
    
    http://aa.usno.navy.mil/data/docs/celnavtable.php
    
    But it's possible I goofed. It's time to get ready for bed so I rushed
    through the check.
    
    Your times are stated to excessive and unjustified precision. The arc
    equivalent of .01s is .15″. But the format of your longitude implies
    it's only known to about .1′, or 6″.
    
    Another issue is whether the time is UT1 or UTC. At .01s precision, the
    difference is highly significant. It may even be necessary to take polar
    motion (which is a few tenths of an arcsecond) into account.
    
    Such accuracy is attainable, though very unnecessary for celestial
    navigation. But the software I would use is on my Windows XP machine and
    the hour is too late to be cranking that up and fiddling with numbers. I
    may try it tomorrow for fun.(?)
    
    

       
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