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    Re: NA daily pages, moon
    From: Frank Reed
    Date: 2008 Oct 31, 01:10 -0400

    Scott, regarding the percent illumination of the Moon, you wrote:
    "Does it have any value for lunars or celnav?  MAYBE."
    
    Well, I can't think of any DIRECT use for celestial navigation that would
    not be met by the simple phase diagram, but I'm still interested in hearing
    ideas (as for lunars, no there would be no use and of course the NA is not
    intended for analyzing lunars in the first place).
    
    And you wrote:
    "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."
    
    That's interesting. Thanks.
    
    And you added:
    "FWIW, I used NVDs in the cockpit back in the 1980s and 1990s."
    
    Just to clarify, when you personally were doing this, did you get your
    percent ilumination data directly from the Nautical Almanac?? Surely, it
    wouldn't be left to each aviatot to dig out the NA just to read off that one
    number, right? I would think that this would be something that would be
    announced on the day of operations, e.g. "tonight the waning Moon is too
    bright, no NVDs after 2030 hours". And it's the sort of thing that only
    needs to be tabulated in one short table --the sort of thing you could stick
    on a single index card-- for the entire year.
    
    And you wrote:
    "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."
    
    It strikes me as a bit of a roundabout solution for a simple problem. Why
    not just stick a light sensor on the NVD? If the Moon's too bright (or the
    aurorae for something else that could cause the same problem), it beeps at
    you.
    
    And you wrote:
    "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."
    
    Ok, you've got me thinking. For sight planning, using a standard sextant (no
    NVD), I could imagine a well-prepared navigator who has carefully determined
    the exact combination of shades required for every level of the Moon's
    illumination. Of course, the Moon's age in days would seem to fit the same
    bill (approximately, not quite the same), and that was in the modern NA from
    the beginning.
    
    Scott, you concluded:
    "I am sure that Lu thinks this explanation is BS too.  He is of course
    entitled to his opinion."
    
    For what it's worth, I personally didn't see anything particularly negative
    in his posts. I didn't see any point where he implied that your comments
    were "BS". I do understand why you took exception to his suggestion that you
    had "assumed" something, and you correctly corrected that. Of course, my
    comments here are merely MY opinion.  :-)
    
     -FER
    
    
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