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    Re: Difficult observations
    From: Greg Rudzinski
    Date: 2009 Nov 20, 12:54 -0800

    Ken,
    
    Maybe the bubble sextant I have isn't a mark 5. The numbers on the
    bottom are AN-5851-1. The lighting is powered by 2 D batteries. The
    magnification seems to be 2X and I can observe the body in the center
    of the bubble as well as adjust the bubble to any desired size. The
    unit also has a two minute averager and a ring to hang on a dome hook.
    There is also a holder for an Elgin stop watch on the bottom.
    
    Greg
    
    On Nov 20, 12:32�pm, Ken Gebhart  wrote:
    > Greg,
    >
    > There is no electrical lighting of the bubble in the Mark 5, so why �
    > should that make a difference? �Also, (if we are talking about the �
    > Navy Mark V) the body SHOULD be placed outside, and alongside of the �
    > bubble. �It is an opaque bubble, not designed to be looked through. �
    > Although it is tempting.
    >
    > Ken Gebhart
    > On Nov 20, 2009, at 7:13 PM, Greg Rudzinski wrote:
    >
    > > Ron,
    >
    > > I find that when the batteries of my Mark 5 bubble go dead that
    > > looking off to the side a bit would help some and even placing the
    > > star outside of the bubble and tangent to the edge would get me in the
    > > ballpark. At sea on my sailboat the bubble can't be used so on the
    > > mark 5 the bubble is removed from view and the visible horizon feature
    > > is flipped into position thus converting to a standard sextant(no good
    > > on New Moon nights). Bubble sextants may not have had this option in
    > > the 30s for Noonan and AE.
    >
    > > Greg
    >
    > > On Nov 20, 9:51 am, Ronald P Barrett  wrote:
    > >> As a long time flight nav (old), I know from an aviation point of �
    > >> view, in the weather, night, turbulent flying, star observations �
    > >> to be difficult, especially with a hand held sextant as flown in �
    > >> the 30s and early 40s. Even worse was a sextant with no averager! �
    > >> One great improvement that was so simple: was the sky-hook. You �
    > >> could they hang onto the sextant and be somewhat more stable in �
    > >> your effort to get a sighting. An even worse condition was when �
    > >> the battery that supplied power to the bubble lamp went dead... �
    > >> you were all but sunk! I often wonder if that was Amelia Earhart's �
    > >> Nav-Noonan's problem on his long 20hr flight in to Howland Island. �
    > >> He had all of the above "worse conditions." Ron Barrett, President �
    > >> Air Force Navigators Observers Association (AFNOA)
    >
    > >> --- On Fri, 11/20/09, Anabasis  wrote:
    >
    > >> From: Anabasis 
    > >> Subject: [NavList 10767] Difficult observations
    > >> To: "NavList" 
    > >> Date: Friday, November 20, 2009, 11:17 AM
    >
    > >> � � In the world of taking observations, as opposed to reducing �
    > >> them, I
    > >> was thinking of the observations that are the most difficult to shoot
    > >> at sea and thought that I�d make a short list. �I am wondering what
    > >> others might think and how they rate different observations in order
    > >> of observation difficulty. �I am not going to list such main stays as
    > >> sun lines, azimuths, and upper transits.
    > >> � � By difficulty I mean to not only observe them, but to get useful
    > >> data. �In any case, here is the list of exotic sights that I�ve taken
    > >> in order of difficulty
    >
    > >> 1) � �High altitude sights of the moon (Ho >89 degrees)
    > >> 2) � �High altitude sights of the sun
    > >> 3) � �Amplitudes of stars/planets
    > >> 4) � �Amplitudes of the moon
    > >> 5) � �Nighttime (by moonlight) star fix
    > >> 6) � �Lower transit of a star (due mostly to low altitude)
    > >> 7) � �Lunar distances
    >
    > >> I�d be interested in hearing what other sights have proven �
    > >> troublesome
    > >> to navigators out there.
    >
    > >> Jeremy
    >
    > >> --
    > >> NavList message boards:www.fer3.com/arc
    > >> Or post by email to: NavList@fer3.com
    > >> To unsubscribe, email NavList+unsubscribe@fer3.com
    >
    > > --
    > > NavList message boards:www.fer3.com/arc
    > > Or post by email to: NavList@fer3.com
    > > To unsubscribe, email NavList+unsubscribe@fer3.com
    
    -- 
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
    To unsubscribe, email NavList+unsubscribe@fer3.com
    

       
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