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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
>>
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>
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