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    Re: Use of Sun Sights for Local time, and Lunars for Longitude
    From: Bruce Stark
    Date: 2002 Oct 23, 18:36 EDT

    It seems to me we're all pretty much in agreement that calculated altitudes
    are OK for clearing a distance. Now, perhaps, more lunars will be taken. On
    land it's so much more convenient to used calculated altitudes, and it only
    takes five or ten minutes to get a set of distances.
    
    I appreciate William Noyce and George Huxtable taking time to explain where
    the thirty-to-one reduction in error comes from. I also appreciate them
    pointing out that in most cases there's no need to repeat the calculations.
    
    Actually, there may be a better way of getting that thirty-to-one reduction
    in the error of the moon's hour angle than the one we've been discussing.
    Here's an excerpt from a posting William Noyce made last April:
    
    >I don't think you need to make any special "local apparent time"
    observations or calculations. Assuming the navigator >has been using
    celestial observations all along, but has an incorrect clock, he will have
    determined a celestial "fix" >whose longitude is off by almost exactly 15'
    for every minute of time error. These two errors will cancel out to >reduce
    errors in computed altitudes, the same way as Bruce Stark's procedure using
    local time. The remaining errors >come from the change in declination (pretty
    fast for the moon), and the difference in rate of change of GHA between >the
    sun, planets, and stars.
    
    Maybe some list members will check this out. Working from local time and
    shifting back and forth between arc and time isn't everyone's idea of fun.
    
    Bruce
    
    
    

       
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