Mr.Lapook , I have recently sent to you texts from Cugle "Practical Navigation" . This manual uses the tables of H.O.no.9-II . The sunset - sunrise method for longitude appears in the imprints 1924 through 1943 . Also in "Precision Astrolabe" by Rogers it is recorded that Portuguese navigators of early transatlantic crossing established longitude at sunrise . It is true that it is an "emergency" fashion , but if no body other than the sun is available , it is the best you have . Mr. Noonan plotted an advanced sunline over Howland in his chart , can anybody answer to the good question how he would have done that without a sunrise observation which also gave him the distance to Howland , 100 mls out @ GMT 1815 ?
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This emergency method is intended for someone without a sextant and so without the ability to measure the height of the sun accurately. In such a case a bare eyeball observation of sunrise might be "the best thing you have", anything is better than nothing. But it was not the "best thing that Noonan had" since he had a sextant and could take shots of the sun at altitudes that allowed for much more accurate position fixes than the range of 40 NM of errors (minimum if used on a ship and much more if tried in flight) using the van Asten sunrise theory. And then van Asten has Noonan dead reckoning for an additional 130 miles adding an additional 13 miles to the band of errors so that Noonan would have had a minimum error band of 53 miles and more likely approaching 100 NM if tried in flight. There was little chance that the van Asten method would get the plane anywhere close enough to see the island. Noonan would have used the standard landfall procedure of taking sextant shots as they neared the LOP and additional ones while tracking the LOP.
see:
https://sites.google.com/site/fredienoonan/topics/landfall-procedureFor those who don't follow the navigational arcana here is a simple way to see why Noonan would never have planned to use a sunrise observation. I think we have all been on a beach watching the sun go down. Think back to your own observations. Were you able to actually see the upper limb of the sun disappear behind the sea horizon? Hmmm? Probably not unless you have looked for it many times. The vast majority of the time there are clouds between you and the horizon and even more clouds beyond the horizon and the sun sinks behind the clouds, not behind the sea horizon. The clouds prevent you from accurately determining the time the sun is actually aligned with the true horizon and every four seconds of error in this timing causes a one nautical mile error in the derived position line. It is an even bigger problem if trying to do this in flight because the horizon is much farther away so providing a much greater opportunity for clouds to block the view. In 2009 I sailed across the Atlantic on the Royal Clipper, see
http://www.fer3.com/arc/m2.aspx?i=110827&y=200911We were 10 days at sea so there were ten sunrises and ten sunsets and I was up every morning before sunrise to shoot the stars and everybody was on deck to catch the sunsets. So, how many sunsets and sunrises was I able to time as the sun set or rose from the sea horizon? just three times out of a possible 20! Clouds blocked the observations 17 out of 20 times. And that was from sea level, on a ship, not in an airplane.
You can repeat this experiment for yourself, just hang out at the beach.
I'm not going to be dragged back into refuting Mr. van Asten's theories one by one which I have responded to before. He keeps bringing them up as if they had not already been refuted. I will use this one example to show the pattern. He now claims that Rogers wrote that the Portuguese navigators (Gago Coutinho) used his method of using sunrise for determining longitude. I wrote before:
"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." (And nowhere near sunrise.)
But van Asten just brings it up again and again, this is his pattern.
Just go back and read the replies starting in May 2011 and you will see that Mr. van Asten's theories don't make any sense.
gl