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 .
Mr. van Asten,
It would be an error to use the marine sextant only if he had computed data for use with a bubble sextant and then only if he were using the "van Asten sunset/sunrise" method which you have never produced any proof whatsoever that it was ever used by anybody, and this includes you, since you have never used it either.
gl
mr.Noonan actually computed data for using the bubble sextant , namely for the sunset fix . Later @ sunrise he accidentally maintained them , but did not continue the use of the b-sextant , replacing it for observation by unarmed eye , telescope , marine sextant , or whatever it may have been . In EJN 2008 I suggested the marine sextant having been used because of it´s green filter against dazzle .
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Mr. van Asten,
Now you are changing your story and talking about a normal sunrise LOP which can be taken with the naked eye by simply observing the upper limb of the sun appear above the visible horizon which, as viewed from an airplane, the sun's altitude is actually below zero. The problem with this is that Noonan did not have a refraction table that showed the refraction correction for altitudes less than 6 degrees above horizontal so would not have been able to make the necessary corrections so as to derive an accurate LOP. The lowest altitude of 6 degrees in his refraction table shows a correction of 8' but for a zero altitude we know that it is 34.5' (you claim 37') He would have been aware of this problem so would not have attempted this. See the refraction correction table in the 1937 edition of H.O. 208 that Noonan was using here:
https://sites.google.com/site/fredienoonan/resources/navigation-tables-for-mariners-and-aviators-h-o-208-dreisonstok-1937/HO208%281937%29.pdf?attredirects=0
It is because you realized that Noonan's refraction table did not allow a "sunrise" observation that you invented the "van Asten" sunrise" concept since you thought it could be computed with the Nautical Almanac's sunrise table which already incorporated refraction in the computation of the times of sunrise and sunset. Now that you have admitted that you couldn't use the sunrise table to compute an accurate time of sunrise, you are back to trying to have Noonan guess at a refraction correction without a table showing corrections for low altitudes.
You wrote in you 2008 paper:
"The Observation Error Translates to a Virtual
Time Error
Figure 3 represents the situation for 1754:53 GMT
when Noonan, coming from the Nukumanu-Nikunau
night flight, observes sunrise, U.L.H., with the
marine sextant preset (+25'.2 arcmin for 1,000 ft
altitude, green filter) for dip and dazzle."
You have the marine sextant set to allow for dip, which is in "van Asten sunrise/sunset" method through which to observe the sun. You did not say that Noonan simply watched the sun appear above the visible horizon.
You can't wiggle out of it now because you have posted way too many times that the problem was caused by Noonan taking the sunrise observation with the marine sextant.
You posted on May 8th on the "Dateline" thread:
"we follow H.O.208 the marine sextant setting for a sunrise observation @ 1,000 ft should be : I. set the index screw to (+) 31´ by which II. the horizon will show up ahead with the instrument held horizontally"
and there are a plethora of other examples where you clearly wrote that he observed the sunrise with the marine sextant preset to 31'.
Another reason that you can't change your story now is that your computations would have shown Noonan more than 28 nautical miles further to the west if he had actually just observed a real sunrise at the time you stated because the sun rises sooner to an observer at altitude. The time you give, 17:54:53 GMT, is the time an observer at 0° 09' north, 178° 47' west at sea level would have observed the upper limb of the sun appear above the visible sea horizon. An observer one thousand feet directly above this spot on earth would have observed the sun appear above the visible sea horizon 1 minute and 52 seconds earlier at 17:53:01 GMT. If you had been claiming that Noonan actually observed the sun rise above the visible sea horizon without using a sextant, just his naked eyeballs, then you would have told us his longitude was 178° 19' west, 28 nautical miles further west than you have constantly claimed in all of your posts and in your 2008 article. The only way to make an observer flying at 1,000 feet note the time of sunrise as being the same time as the observer at sea level directly below him notes the time of sunrise is to use the "van Asten sunrise/sunset" method with the flying observer using a marine sextant set to 31'.
Nice try.
gl