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    Re: NA daily pages, moon
    From: Scott Owen
    Date: 2008 Oct 30, 21:27 -0500

    frankreed{at}HistoricalAtlas.net wrote:
    > But I think there's general agreement that
    > the data in that little moon box have very limited navigational value. For
    > another example, why do we need to know the moon's percent illumination (to
    > the nearest percent)? The percent illumination was added in the 1980s. Why
    > wasn't the small phase diagram sufficient?
    >
    >  -FER
    
    Frank,
    Does it have any value for lunars or celnav?  MAYBE.  However, it does
    have value depending on HOW/WHERE you do your navigating... say flying
    from a ship at night.  The moon's percent illumination is given to the
    nearest percent because Naval Aviators use percent moon illumination for
    maximum moon illumination requirements for flying at night using night
    vision devices [NVDs].  That is, if the moon illumination is too bright
    you can NOT use NVDs because of NOT being able to see the cockpit
    instrument panel while flying on NVDs.  IIRC, the requirement was to the
    nearest percent and not the nearest 5 or 10 percent.  FWIW, I used NVDs
    in the cockpit back in the 1980s and 1990s.  Of course, there may be
    other uses for percent moon illumination, I just know what I used it for
    10-20 years ago and is still used today wherever NVDs and flying at
    night from a ship come together.
    
    As to the value of percent illumination to lunars or celnav... well, if
    you hooked up a 5th generation NVD to a sextant... there actually might
    be some nights when you couldn't effectively use the Sextant/NVD
    combination.  At some percent moon illumination it would be too bright
    to use the NVD for celestial shots.  The navigator [once the max moon
    illumination is known] might want to change to a different optical
    device before sunset using a quick glance at the NA.
    
    I am sure that Lu thinks this explanation is BS too.  He is of course
    entitled to his opinion.
    
    --Scott
    
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