NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2009 Nov 17, 04:27 -0800
gl
Gary J. LaPook wrote:
Frank asked:
I remember a discussion a few years ago of a proposed theory claiming that Noonan didn't understand the correction for the Moon's parallax... that theory struck me as pretty light-weight at the time. Can we dismiss it? Yes, we con put a stake through its heart. The question of the Moon has relevance since it would have been available during the day as they approached Howland island and would have provided a good cut to the sun line allowing for a fix. TIGHAR's theory is that Noonan knew he was on the 157º-337º sun line LOP (from Earhart's last transmission) but didn't know where he was located north or south along this line so just blithely followed it to the south to finally arrive, after 350 NM, at Nikumaroro( then Gardner) island. The availability of the Moon line shoots down this contention which puts a nail in TIGHAR's coffin.The "Death By Parallax" web page
http://www.bbc.co.uk/dna/h2g2/A3694854
has the basic navigation wrong. First it states
that the moon passed 20º south of Howland at 7:01 am (1831Z) when, in
fact the moon passed NORTH of Howland at 1837Z and its altitude was 76º
56' at that point since its declination was 13º52' North ( see Nautical Almanac for 1937, attached) and the latitude of Howland is 0º 48' North.
The "horizontal parallax" of the moon at that time was 59.2' from the
above almanac page. But that amount of parallax exists only if the altitude of the
moon was horizontal or zero degrees. To find the correction that must be
applied to the sextant altitude you must multiply the horizontal
parallax by the cosine of the altitude. When you do this you find that
the error in omitting the "parallax in altitude" correction only comes
to 13.4' which is the same as 13.4 nautical miles because of the Moon's high altitude of
76º 56' at that point.
If Noonan had omitted the "P in A" correction then the plane would have been 13.4 NM north of
where he thought it was so he would have been north of Howland and he would have stumbled onto Howland while
following the sun line on the heading of 157º T. If they had not seen Howland then they would have seen Baker island which is also on the 157º-337º sun line LOP 42 NM south east of Howland. In order to miss both of these islands with the 20 NM visibility reported by Itasca the plane would have had to have passed more than 62 NM south of Howland and no likely error in the moon line could have produced an error that large.
At the time of their last transmission at 1912 Z the altitude of the
moon was still high at 75º 41' so the "P in A" correction was still only 15.1' or 15.1
NM and the azimuth of the moon was 328º T so omitting the correction
would still place them north of the island.
However it is very unlikely that Noonan could have made this mistake
since the navigation table he was using, HO 208, Dreisenstok, has the
"MOON" correction table on the very first page, just inside the cover,
and this table incorporates the "parallax in altitude" correction with the
refraction correction. Adjacent to this table, and on the same page, is
the table for "Sun or Star" which only has the refraction correction.
These very same tables are also found in all the commonly available
tables of the time including HO 211 and the Weems Line of Position Book
going back at least as far as 1927. This table does not incorporate a
correction for semi diameter since it is for use with a bubble sextant
such as Noonan was using.
BTW, the horizontal parallax is calculated by taking the arc sin of (
the radius of the earth, 3440 NM, divided by the distance to the moon.)
Since this distance varies during the month from 196,164 NM to 218,954
NM the H.P. varies from 60' down to 54'.
gl
Gary LaPook wrote:1. Most likely he was using a Pioneer octant similar to the A-5 but there is no record showing for sure what kind of octant he was using. See: http://www.fer3.com/arc/imgx/A-5-Manual.pdf 2. TIGHAR claims that he was also carrying a marine sextant. They base this claim on a letter written by Noonan to Weems in which he describes the equipment carried on the much larger Pan Am Clippers including a marine sextant as a "preventer." There is no reason to believe that he carried one in the much smaller Electra, no records, no testimony, and not on the Luke Field inventory (after the takeoff accident.) 3. Mary S. Lovell's 1987 book, "The Sound Of Wings" discusses the different coordinates for the island. Lovell writes that Williams had used the coordinates listed in "Lippencott's Geographical Dictionary of the World" and also used by the Navy;s Hydrographic Office, as 0º 49' 00" north and 176º 43' 09" west. She also states that Itasca had corrected the coordinates of Howland on the 1936 cruise but that those had not been published by the time Williams had consulted the Hydrographer's office. That position published in the 1938 edition of Bowditch was 0 ° 48' N, 176 ° 38' W. The previous position had been given about 5 NM further to the west but Noonan may have had the correct position to work with. Assuming that he computed his LOP to hit that spot five miles to the westward and assuming normal accuracy of a celestial LOP shot from a plane is 7 NM ( I will not explain why this is so) then if that error placed them to the west of that LOP they would still pass only 12 NM west of Howland so should have been able to see it given the 20 NM visibility reported by Itasca. If the error was less or if it put them to the east of the LOP they could have passed much closer and, possibly, right over Howland. The position of Howland from Google Earth shows the southern tip at 0º 47.7' N, 176º 36.9' W. The northern tip is 0º 49.2' N. 176º 37.4'W. The farthest west shore is at 176º 37.5' W and the eastern shore is 176º 36.7' W. The average of these is about 0º 48.5'N, 176º 37.0' W about a mile east of the position given in Bowditch. I decided to do some more checking on the accuracy of Google Earth coordinates to make sure they were accurate in the Pacific. I found the published coordinates of Mili airport, 6º 05' N, 171º 44'E; Mujuro airport, 7º 03' 44'' N, 171º 16' 19" E; and Kosrae airport, 5º 21' 25" N, 162º 53' 30"E since these were the closest to Howland. Then going to them with Google Earth I found that the Google Earth coordinates were exactly right, correct to the accuracy of the positions given in the airport database. Mili was only given to the nearest minute but the others were to the second. ( A second is only 100 feet!) You can check for yourself, just go to Google Earth with those coordinates which you will see fall on the runways. The only coordinates that have any relevance are those for where Howland is actually located, which we now know to a high level of accuracy, and the coordinates known to Noonan that he was aiming for. The difference, if any, would be the size of any built in error in following the LOP to the island. If Noonan was using the 176º 43' W value then he was aiming about five or five and a half NM west of the western shoreline of Howland. If he was using the 176º 38'W value he was aiming within one half mile of the shoreline. Either way they should have been able to see the island. In looking at the location of Howland and how possibly wrong coordinates for the island may have contributed to Noonan missing the island we have all forgotten an important fact, Itasca was making smoke. Smoke from ships can extend for great distances and be seen for many miles. It was these smoke trails on the horizon that U-boats searched for when trying to find a ship to attack. Smoke is made on purpose by spraying unburned fuel oil into the exhaust stack much like smoke is made on air show aircraft. All of the descriptions and the photos of the smoke screen being made by Itasca say that instead of rising high up in the air that the smoke was blown downwind. The wind was out of the east. This means that the smoke would have been blown many miles downwind, to the WEST, probably more than ten miles (Safford) and beyond the erroneous coordinates given for Howland and probably much farther. This means that even if Noonan had been aiming for the erroneous coordinates he would certainly have seen the smoke and followed it to Howland. Water don't burn. If they saw the smoke they would have known that there was something at the end of the smoke trail, a ship or an island, either of which wold have been a better than splashing down in the ocean. And it wouldn't take them very long to follow it to the end to see what was making the smoke even if they went the wrong way at first. Since they had been fighting a headwind all the way they knew that the wind was out of the east so if they saw the smoke they would have known to follow it to its source, to the east. 4. The equipment carried on the abortive westbound attempt was inventoried after the takeoff accident at Luke Field. No known list of equipment carried on subsequent attempt. 5. They would have taken the sights at cruising altitude, about ten thousand feet using the bubble octant. One of many reasons to not use a marine sextant is the very large dip correction from high altitude which has a great uncertainty due to the uncertainty in the altimeter. Also, at ten thousand feet, the horizon is 130 NM away and it is very unlikely that you would be able to see all the way to the natural horizon due to limited visibility. Using a marine sextant Chichester had to descend down almost to the sea so that he could calibrate his altimeter and then climbed to one thousand feet to take the observation. 6. The story about the moon's parallax was all hooey. Noonan used Dreisenstock. On the first page are the sextant correction tables, one for sun and stars and one for the moon. The moon correction table combines the P in A correction with the refraction correction so there is was no way for Noonan to correct a moon observation without allowing for P in A. See attached. gl frankreed@HistoricalAtlas.com wrote:I thought it might be interesting to get a conversation going about Amelia Earhart's navigation --really Fred Noonan's navigation-- on their ill-fated circum-navigation back in 1937. There's a movie opening this week, "Amelia", produced by and starring Hilary Swank as Earhart. It's getting beat up pretty bad in the early reviews (currently at a dismal 22% fresh on RottenTomatoes.com: http://www.rottentomatoes.com/m/amelia_2009/), but I'm sure many of us will see it eventually. So... I know next to nothing about their navigation. Gary Lapook knows lots, and I expect I'm setting you up for some typing, Gary. :-) I'll just start off with some basic questions: what kind of sextant did they carry on that flight? Did they have multiple instruments? Were their different instruments during various legs of the flight? At what altitude would sights have been taken (or did it matter)? I remember a discussion a few years ago of a proposed theory claiming that Noonan didn't understand the correction for the Moon's parallax... that theory struck me as pretty light-weight at the time. Can we dismiss it? Did Earhart herself know any celestial navigation? Thanks in advance to any and all who can fill me in on this. -FER PS: Hey, Gary: when you visited Mystic back in 2008, did you get a chance to drive by the house where Amelia married George Putnam in Noank?
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