Any ex-marine air navigator of the era certainly knew about the for the sun zero altitude refraction , then figured 37 arcminutes . Be it not from H.O.208
or other tables , every textbook and the nautical almanacs contained chapters on the subject . Conyers Nesbit , professional navigator , in articles (*) and a book refers to mr.Noonan´s supposed ability to derive a more or less accurate geographical position from observing sunset and sunrise . It is not even necessary to observe for the instant : if the time-position group is precomputed and sunset-sunrise superficially observed from an aircraft , one acquires an indication for being with acceptable uncertainty in the vicinity of the precomputed coordinates pair . Mr.Noonan may have used this fashion when near Nukumanu Island he announced his position at 0718 GMT (mr.Chater´s watch time) , whereas actual sunset was at 0719:30 GMT , as mentioned in the addenda on EJN articles of July 2008 and April 2011 . We do not know it by certainty , but he may have also used it for sunrise in the roads of Howland .
(*) Aeroplane Monthly , Jan and Feb ,
1989 .
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