Mr. Lapook ,
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
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I forgot to say that the accuracy of marine sextant sights was determined for observations taken on shipboard where the height of eye above sea level was measured so there was no uncertainty in the dip correction to be use. There is no reason to believe that an in-flight marine sextant observation would be more accurate than a shipboard observation and would probably be less accurate but there are no statistics on that BECAUSE NO ONE USES A MARINE SEXTANT IN FLIGHT!
gl
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
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Chichester, Coutinho and several other early pioneering aviators did use marine sextant but this was only because bubble sextants had not yet been perfected. During the 1910's and 1920' rapid progress was made in improving and perfecting bubble sextants, with many false paths until it all came together, the right lenses and, most importantly, the right curvature to the top of the bubble chamber.
You can read about these developments here:
http://www.fer3.com/arc/imgx/Bubble-sextants-Precision-Astrolabe.pdfBy the early 1930's the bubble sextant had been perfected so no one used a marine sextant after that to take observations from airplanes.
I sent this to him before:
"It is interesting that you list some early aviators implying that they used your sunrise method, do
you have any sources for this claim? Ellsworth used a bubble sextant, Lindbergh used a Pioneer
bubble sextant (there is a photo of his navigation equipment in Weems, 1938). They all used the standard Line Of Position computation, not your "van Asten sunrise" method. I have analyzed
Chichester’s navigation extensively and he used a marine sextant to take five sextant
observations on the New Zealand to Norfolk Island flight in 1931, all were in the range of 23° 12' to 50°
50'. On the next leg to Lord Howe Island he also took five observations, all in the range of 23° 48'
to 53° 42'. So contrary to your claim, none of his observations were anywhere near a zero altitude
or a sunrise sight. "
Coutinho in 1922 took 40 observations with a mariner's sextant but the lowest altitude he measured was 16° 15', nowhere near the "van Asten horizon."
Mr van Asten also mentioned that these early aviators precomputed their sights and although that may be true what they precomputed were the normal "computed altitudes" used for the normal Line Of Position navigation method, not for the "van Austen sunset/sunrise" method. It appears that Mr. van Austen doesn't understand how these precomputations were done. Here is link to many flight navigation manuals that explain this procedure and he might get some value from reading them.
https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curvesI have asked Mr. van Austen repeatedly to produce any proof that he might have that anybody ever used his method and he has never produced a thing.
gl