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Author Topic: Why 10AM from Lae?  (Read 62010 times)

h.a.c. van asten

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Re: Why 10AM from Lae?
« Reply #15 on: May 25, 2011, 10:25:11 AM »

G.Lapk. Sine the Almanac sunrise time is in L.Mean.T. , the correct U.L. sunrise time at any meridian around the world can be found by applying the latitude in time units to the Almanac (interpolated) figures. The reason is that Mean Time is registered by an artifical sun , orbiting the celestial horizon with unifform acceleration at exactly 15 deg / hr. If checked by the spherics formula for sunrise U.L. at any meridian , a same sunrise time like by the Almanac listing is consistently found in hours, minutes and seconds. Seconds digits are not listed in the Almanac , outcomes are finished to minutes.
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Gary LaPook

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Re: Why 10AM from Lae?
« Reply #16 on: May 26, 2011, 09:44:17 PM »

G.Lapk. Sine the Almanac sunrise time is in L.Mean.T. , the correct U.L. sunrise time at any meridian around the world can be found by applying the latitude in time units to the Almanac (interpolated) figures. The reason is that Mean Time is registered by an artifical sun , orbiting the celestial horizon with unifform acceleration at exactly 15 deg / hr. If checked by the spherics formula for sunrise U.L. at any meridian , a same sunrise time like by the Almanac listing is consistently found in hours, minutes and seconds. Seconds digits are not listed in the Almanac , outcomes are finished to minutes.

--------------------------------------------------------------------------------
You are attempting to use the sunrise table for a purpose it was not designed for.
You must know the general rule that you can not go beyond the precision of your data but you
somehow attempt to massage the data in the sunrise table to get a greater level of precision than
the level of precision existing
in the original data. The sunrise table in the Nautical Almanac is only approximate and is only to
a precision of plus and minus 30 seconds (only to the nearest whole minute (and only at the
Greenwich meridian) and then for a three day period) and  is used for planning purposes only and
not for actual celestial navigation calculations. It is the main data tabulated in the almanac for
declination and Greenwich Hour Angle  that are actually used for celestial navigation
computations. The most important use of the sunrise  table is so the marine navigator can
set his alarm clock so that he gets out of bed early enough to take a morning round or stars on
ship board during the short twilight period when the stars are still visible and the horizon has also
become visible. It has no such importance for a flight navigator since he can take star sights all
night
long with his bubble sextant so the twilight period is not important to him. Another use of it for a
marine navigator is by looking at the sunrise or sunset table (and the twilight tables) and then at
the derived time entry for Aries he knows the approximate LHA Aries at twilight so can easily
use H.O. 249 volume 1 for selected stars to preplan his shooting schedule.

 A really simple way to show that the sunrise table can’t be used in the manner that you attempt
to use it is to look at the subsequent three day period starting, with July 5th, where it gives the
time of sunrise as 0601, exactly one minute later than the 0600 time given for the period of July 1
though 4 that you used. Ask yourself this question, how did the time of sunrise change by exactly
one whole minute between July 4th and 5th? Did the earth stop rotating for exactly one minute and
then start rotating again?

Basic to your premise is your computation of the time of sunrise at the location that you think the
plane was, at the time of sunrise.  You step  through this computation like this on page 28 of the
2008 article:


“Offset Fix had to be established. In
Noonan's case with the aireraft's 150 mph cruise
speed, this Fix had to be precomputed forthe coordinates
pair (178?47'-W;OOOO9'-N) at 150 mis off
The belonging sunrise time was charted in the
(American) Nautical Almanac (an Air Almanac was
not issued for the year).
Lat 00 deg LMT 0600
July 2,3,4 U.L.H.
Lat 10 deg N LMT 0543
For 00009'-N we find LMT 0600 - 9/600 x 17m =
0559:45 LMT. By adding the West longitude in time
units (I Ih55m08s) it is found that Upper Limb Sunrise
for the Offset Course Shift was at 1754:53 GMT.”


( A navigator would never do the time computations that you did especially he would never use
GAT since the Nautical Almanac in 1937 used GMT for all the tabulations which were for GHA,
not right ascension, and Noonan said himself that:

 “I consider the development the Greenwich hour- angle idea the greatest contribution to the
science
of navigation since Sumner, and have used it exclusively since first published in the Air
Almanac.”  See:

https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0

What you are doing here is assuming that the plane was located at 178? 47' west and 0? 09' north
and then calculating the time that the sun would have risen at that location. We only have to look
at
the first part of that computation since the problem there carries through all the rest of your
computations. You looked at the “Sunrise- Sunset” table for July 2, 1937 (you actually must have
looked at a modern Nautical Almanac because there was no such table in the 1937 so Noonan
couldn’t have done the computation that you did, nor would he have wanted to.)  The tabulated
values are
only correct for the middle day of a three day period, which was July 3rd (in the modern almanac
you used. The 1937 almanac was not arranged in three day periods) and you found that sunrise on
the equator was at 0600 and that sunrise at 10? north was at 0543. You then did a straight line
interpolation between these two values to determine the time of sunrise nine NM north of the
equator
at 09' north as 0559:45.

“What is wrong with this picture?”

The most obvious problem is that the data in the table you used is only tabulated to the nearest
minute so no
matter what you do after that with this data it can never be more accurate than the level of the
original data. Based on your tabulated values, the sunrise on the equator (on July 3rd not the 2nd)
was
somewhere between 0559:30 and 0600:30 and the
sunrise at 10? north was somewhere between 0542:30 and 0543:30 with no way to know exactly
where within these ranges. The uncertainty range of plus and
minus 30 seconds in the original tabulated data must be applied to your calculated time so, using
your
method, the time of sunrise at 00? 09' north could have been anywhere between 0559:15 and
0600:15  yet you nail it exactly to
the
second at 0559:45. The “Sunrise- Sunset” table in the Nautical Almanac carries a warning that
when
interpolating for times of sunrise that: “rounding errors may accumulate to about 2 minutes.”
You ignored this warning.

Why is this important?

You may think that I am picking nits, but this 60 seconds of uncertainty in the time causes a 15
NM uncertainty in the derived longitude because the sun is traveling west along the equator at
900
knots, 15 NM per minute. All of your subsequent calculations flow from this calculated time of
sunrise.
At the end of your computations you come up with an error in Noonan’s longitude of just 9 NM
so your
result is swamped by the actual uncertainty in your original calculation of the time of sunrise so
your calculation has
no significance. You also forgot that Itasca was making smoke that blew downwind much further
than the 9 mile error that you claim Noonan made.


Gary LaPook
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Ric Gillespie

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Re: Why 10AM from Lae?
« Reply #17 on: May 27, 2011, 05:55:41 PM »

Thank you Gary.  I actually understood most of that.
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h.a.c. van asten

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Re: Why 10AM from Lae?
« Reply #18 on: May 29, 2011, 03:03:09 PM »

G.Lapk  If you apply and work the formula for U.L. sunrise @ 178-47-W ; 00-09´-N , you find the very same sunrise time as by N.A.table. If you want it simpler , calculate central sunrise with the short formula (cos LHA = - tan d . tan L) and subtract 53´/ 13´.8 = 3m50s , in which 13´.8 is the sun´s rising velocity in time minutes , and you will again find the very same outcome , also to be found by H.O.208 , Table II. There is no reason to doubt that Noonan , after succesfully establishing position by the sunset fix near Nukumanu , would also be able to finish a sunrise fix before trying to find Howland.
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Gary LaPook

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Re: Why 10AM from Lae?
« Reply #19 on: May 29, 2011, 05:40:22 PM »

G.Lapk  If you apply and work the formula for U.L. sunrise @ 178-47-W ; 00-09´-N , you find the very same sunrise time as by N.A.table. If you want it simpler , calculate central sunrise with the short formula (cos LHA = - tan d . tan L) and subtract 53´/ 13´.8 = 3m50s , in which 13´.8 is the sun´s rising velocity in time minutes , and you will again find the very same outcome , also to be found by H.O.208 , Table II. There is no reason to doubt that Noonan , after succesfully establishing position by the sunset fix near Nukumanu , would also be able to finish a sunrise fix before trying to find Howland.

----------------------------------------------------

That is true, if you calculate the time of sunrise for July 2, 1937 for the position you chose using the actual data in the Nautical Almanac and a calculator then you do find the time of sunrise to be very close to the time you calculated by using the incorrect method by use of the sunrise table. This is only a coincidence.

Using your method of using the sunrise table you will calculate the same exact time of sunrise, 5:59:45 local time at the position you chose of nine minutes north latitude and at every longitude on earth for the entire three day period of the tabulated sunrise value. However, if you do the actual computation you will find that the time of sunrise will vary by 32 seconds at that latitude during that period so you just got lucky that at the location you chose that the computed time worked out right.   

 But
this is only a coincidence and does not work for other longitudes and other days in the three day
period covered by the tabulated value in the Nautical Almanac table. For example, if they were
flying one day later, then the true altitude of the sun’s center at the same time and location would
have been -55.5' causing sunrise to occur ten seconds later at 5:59:55 and resulting in a 2.5' error in
longitude. If they flew two days later (still within the period of the tabulated sunrise table) the
sun’s center would have been at -58.1' causing sunrise to be delayed by 20 seconds so the sun would
nor have risen until 6:00:05 and resulting in a 5.1' error in longitude.

-------------------------------------------------------------------------

(This is the boring calculations and you can skip down to the next section if you choose.)

You calculated sunrise (center of sun 53' below the horizon) at 178° 47' West and 00° 09' North
latitude as 5:59:45 LMT using the sunrise table. By an amazing coincidence the actual
computation works out very close to that, I calculated -52.9' the same as your calculated -53'. But
this is only a coincidence and does not work for other longitudes and other days in the three day
period covered by the tabulated values in the Nautical Almanac table. For example, if they were
flying one day later, then the true altitude of the sun’s center at the same time and location would
have been -55.5' causing sunrise to occur ten seconds later and resulting in a 2.5' error in
longitude. If they flew two days later (still within the period of the tabulated sunrise table) the
sun’s center would have been at -58.1' causing sunrise to be delayed by 20 seconds and resulting
in a 5.1' error in longitude. That three day tabulation would be used for sunrises starting at 89° 56'
East on July 2nd and continuing until
the sunrise at the same longitude on July 5th.  At nine minutes north latitude and at 89° 56' east, at
5:59:45 LMT on July 2nd (0000 GMT July 2nd) the center of the sun was -51.1' meaning the sun
would have risen 8 seconds earlier and causing 1.9' error in longitude. Three days later (2400
GMT July 4th) at the same location (and using the same tabulation from the sunrise table, using
your method) the sun’s actual center was -59.0' meaning that the sun rose 24 seconds later than
you would have calculated and resulting in a 6.0' error in longitude. So you see your result was
just a lucky coincidence.

-------------------------------------------------
(Start reading again here.)



 

I also note that you have now changed your basic premise stated in your papers that Noonan could have just used the sunset and sunrise tables in the Nautical almanac since I have shown you (off list)  that the computation cannot be done this way. There are no instructions in Dreisonstok on how to use these tables in this unforeseen way nor have I found it in any edition of Dutton of Bowditch or in any of the flight navigation manuals that I have.

 

You might be able to use the tables in H.O. 208 to do that calculation but what makes you
believe that Noonan or any other flight navigator could do that? (By the way, how long did it take
you to work out that method?) There are certainly no instructions in H.O. 208 to show a
navigator how to make that computation. Nor is there any discussion of doing such a
computation in any of the flight navigation manuals or even in Bowditch or Dutton. Can you
point to any navigation manuals that instructs a navigator to make such a computation?


It is interesting discussing theoretical celestial navigation with you but your methods were never
taught to navigators so there is no reason to believe that Noonan just came up with your method
all on his own. You have really fallen in love with the sunrise observation but you won’t find that
method in navigation manuals. Can you point out a manual that teaches your method for finding
longitude?

This sunrise is only used as a way to introduce the basic concepts for finding longitude to
celestial navigation students but it is not used in practice. Even in the olden days before Sumner
and the “new navigation”, navigators used the time sight for finding longitude and took the
observation when the body was on the prime vertical, not at sunrise. Navigators were told not to
take low altitude sights for this purpose and I sent you excerpts from Bowditch, 1863 and 1914 and
from Wrinkles in Navigation, 1884, for your review but nobody used these methods to determine
longitude by Noonan's time, everybody used the simpler Sumner line (LOP.)  The reason that H.O. 208 and other “short
methods “ were developed was to simplify the calculations that a navigator had to do, not to
make them more difficult.
Remember, for a navigator this is drudge work and, especially for a
flight navigator, it is important to reduce the time required for the calculations and to reduce the
opportunities for math errors. To this end, navigators learn one method and stick with it
throughout their careers even as newer methods are developed.  Noonan said exactly this in his
letter to Weems. see page 425:

https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0

So there is certainly no reason to believe that Noonan would try to go back to what he may have
remembered from his high school trig class to develop and try out for the first time the  novel and
theoretical method that you advocate for finding longitude on this very critical navigation leg.

Gary LaPook
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h.a.c. van asten

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Re: Why 10AM from Lae?
« Reply #20 on: May 30, 2011, 02:34:41 PM »

GLapk. In the 1930´s a well known problem in nav. textbooks was : "You see sunrise @ x-time. Determine your longitude" . And I repeat : why would Noonan be succesful operating a sunset fix (EJN-2011) , whereas next morning he would not be able to duplicate it for sunrise ? H.O.208 namely , by it´s Table II delivers a comfortable fashion to compute longitude by sunrise time : you observe sunrise U.L. and note GMTime.
By precomputed multiplication  tan declination with tan latitude you obtain cos LHA , reduce by Tab.II to LHA . Add GHA to LHA , subtract from 180 deg and you have the longitude , a conservative calculation for sea (later air-) navigators of the era. There are no by accident outcomes , easily checked by comparison of Table results with direct spherics. If you have computed for central sunrise and you need sunrise U.L. , you subtract 3m50s (not time eq. but time needed for sun to orbit sun from -53´ to 0´) and your time and longitude  to be reduced from marine sextant observation are established. Why would we learn it in an evening , whereas a professional navigator with full scan long period precomputation experience would not know it ?
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Gary LaPook

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Re: Why 10AM from Lae?
« Reply #21 on: May 31, 2011, 12:58:42 AM »

GLapk. In the 1930´s a well known problem in nav. textbooks was : "You see sunrise @ x-time. Determine your longitude" . And I repeat : why would Noonan be succesful operating a sunset fix (EJN-2011) , whereas next morning he would not be able to duplicate it for sunrise ? H.O.208 namely , by it´s Table II delivers a comfortable fashion to compute longitude by sunrise time : you observe sunrise U.L. and note GMTime.
By precomputed multiplication  tan declination with tan latitude you obtain cos LHA , reduce by Tab.II to LHA . Add GHA to LHA , subtract from 180 deg and you have the longitude , a conservative calculation for sea (later air-) navigators of the era. There are no by accident outcomes , easily checked by comparison of Table results with direct spherics. If you have computed for central sunrise and you need sunrise U.L. , you subtract 3m50s (not time eq. but time needed for sun to orbit sun from -53´ to 0´) and your time and longitude  to be reduced from marine sextant observation are established. Why would we learn it in an evening , whereas a professional navigator with full scan long period precomputation experience would not know it ?

---------------------------------------------------
Mr. van Asten,

I have asked you before to give the titles of any flight navigation manuals that tell a flight navigator that calculating the time of sunrise is a desirable way to determine longitude and all you now come up with is;

"In the 1930´s a well known problem in nav. textbooks was : "You see sunrise @ x-time. Determine your longitude""

I also pointed out that a discussion of sunrise in basic navigation textbooks was only used as a way to introduce student navigators to the concepts of how longitude relates to time and that the use of sunrise is not the way longitude was actually determined by navigators in the real world, even back in the 19th century and certainly not in the 20th century. It appears that you may be referring to some beginner level basic navigation training text book used in school, not to navigation manuals actually used by navigators. It also sounds like you may possibly be referring to old basic navigation textbooks from the 19th century because longitude was not determined separately by 20th century navigators since the 20th century method was to determine lines of position. In the 19th century "time sights" were used (a very different procedure than a sunrise observation) for separately determining longitude but this was before the development of the modern line of position method used by Noonan and all 20th  century navigators for finding fixes.  Even in the 19th century, a discussion of sunrise in a basic navigation textbook was only a  way of introducing the concepts necessary for finding longitude to student navigators because even in the 19th century "time sights" were used, not sunrise observations. I also pointed out to you that a sunrise observation is a poor way to determine longitude because any error in the assumed latitude, when doing the calculation, results in an error in the longitude that you determine.

I have also pointed out to you another reason that a sunrise observation is not used for navigation is due to the large uncertainty in the refraction at low altitudes so that all the navigation texts and manuals, then and now, advise against taking low altitude sights.

The American Practical Navigator, Bowditch, H.O. 9, 1938 ed., (the standard navigation reference book of the U.S. Navy) has this to say about low altitude sights: "Under certain conditions of the atmosphere a very extraordinary deflection occurs in rays of light which reach the observer's eyes from the visible horizon, the amount of which is not covered by the normal corrections for pressure and temperature; on account of it, altitude less that 5° should be avoided." This advice is continued in more recent editions of Bowditch. Other examples, the 1888 through 1914 editions, said to avoid altitudes below 10°.
See: https://sites.google.com/site/fredienoonan/resources/american-practical-naigator-h-o-9-1914
https://sites.google.com/site/fredienoonan/resources/american-practical-navigator-1888



The 1937 Nautical Almanac and the 1937 edition of H.O. 208 (the navigation references used by Noonan) did not even have tables to allow the use of observations of less that six degrees above the horizon so could not even be used for a zero degree, sunrise observation. You just refuse to accept these facts. Off list I have asked you questions relating to the use of the refraction correction table and it is clear from your answers that you misunderstand how to use this table.


Navigation and Nautical Astronomy Dutton, 1934 ed. (the official textbook at the U.S. Naval Academy) states that due to the large unpredictable variations in refraction, that the time of sunrise can vary by TWO MINUTES which would cause an uncertainty of 30 nautical miles in a position determined by a navigator using your method for determining longitude by observing sunrise.
See: https://sites.google.com/site/fredienoonan/topics/refraction

H.O. 218, "Astronomical navigation Tables," first published in 1938, was a table of precomputed altitudes and azimuths for use by flight navigators and was an improvement on, and a replacement for, H.O. 208. Since all navigators knew not to take low altitude sights, the lowest altitudes tabulated in this more modern set of tables was 10°. For some reason you do not understand that a "sunrise sight" is nothing more than a zero degree altitude sight with all the uncertainties mentioned in the standard reference works. 

And now, only after I showed you that the method of calculating the time of sunrise that you published in your 2008 and 2011 papers by using the sunrise table in the Nautical Almanac, that were never intended for that purpose, and that navigators only use its approximate values for planning purposes, and would never think to use it in the manner that you described, you now have invented a new, esoteric, unintended use of the information contained in H.O. 208 to do this calculation. You may be a mathematician with plenty of time on your hands to conjure up novel ways to do trigonometric computations, but there is no reason to think that Noonan or any other navigator would attempt to do the same. There are no instructions in H.O. 208 itself or any other navigation manual describing your creative use of these tables. H.O. 208 was designed for one purpose only and that was to calculate lines of positions and the tables are organized and optimized for that one purpose and the instructions contained in H.O. 208 show only that use of the tables. Noonan said in his letter to Weems that he used H.O. 208 (Dreisonstok) method exclusively meaning he used the method in H.O. 208, not just the tables in it,  to calculate lines of position and he would have had no reason to try to deviate from his normal, practiced, and exclusive use of the H.O. 208 method to invent some esoteric use of these tables as you describe.

See: https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG

The entire sections on finding longitude from the 1888 and 1914 editions of the American Practical Navigator are posted here:

https://sites.google.com/site/fredienoonan/resources/american-practical-navigator-1888

and

https://sites.google.com/site/fredienoonan/resources/american-practical-naigator-h-o-9-1914

There is no mention of using your sunrise method.

----------------------------------------------------------------------------------------------------------------------------

You have told me that you have over a hundred navigation texts in your library so please give us the titles of any

A.) flight navigation manuals that tell a flight navigator that calculating the time of sunrise is a desirable way to determine longitude;

B.) any 19th or 20th century texts that show using sunrise as a way to determine longitude;

C.) any 20th century texts, marine or flight, that show the calculation of sunrise to an accuracy of one second of time by use of the Nautical Almanac sunrise table;

D.) any 20th century texts, marine or flight, showing your new method of calculating the time of sunrise;

E.) any 20th century texts, marine or flight, showing how to use the tables in H.O. 208 to calculate the time of sunrise.

Gary LaPook


;

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Gary LaPook

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Re: Why 10AM from Lae?
« Reply #22 on: May 31, 2011, 01:44:26 AM »

GLapk. In the 1930´s a well known problem in nav. textbooks was : "You see sunrise @ x-time. Determine your longitude" . And I repeat : why would Noonan be succesful operating a sunset fix (EJN-2011) , whereas next morning he would not be able to duplicate it for sunrise ? H.O.208 namely , by it´s Table II delivers a comfortable fashion to compute longitude by sunrise time : you observe sunrise U.L. and note GMTime.
By precomputed multiplication  tan declination with tan latitude you obtain cos LHA , reduce by Tab.II to LHA . Add GHA to LHA , subtract from 180 deg and you have the longitude , a conservative calculation for sea (later air-) navigators of the era. There are no by accident outcomes , easily checked by comparison of Table results with direct spherics. If you have computed for central sunrise and you need sunrise U.L. , you subtract 3m50s (not time eq. but time needed for sun to orbit sun from -53´ to 0´) and your time and longitude  to be reduced from marine sextant observation are established. Why would we learn it in an evening , whereas a professional navigator with full scan long period precomputation experience would not know it ?


--------------------------------------------------------------
I didn't respond to you question. You asked:

"And I repeat : why would Noonan be succesful operating a sunset fix (EJN-2011) , whereas next morning he would not be able to duplicate it for sunrise ?"

The answer is that he didn't do a "sunset fix" either for the same reasons stated in my prior post. Your "sunset fix" is another invention of yours based again on your lack of understanding of how flight navigation is actually done.  For a more detailed answer see my prior post.

Gary LaPook
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Ric Gillespie

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Re: Why 10AM from Lae?
« Reply #23 on: May 31, 2011, 06:59:00 AM »

This has been an educational exchange but I think Gary LaPook has adequately demonstrated that Mr. van Asten's speculation about Noonan's navigation on the Lae/Howland flight is founded more upon his own creativity than upon any documented practice by aerial navigators in general or by Fred Noonan in particular. It's pretty clear that no one is going to change Mr. van Asten's mind but I hope he will at least accept that this forum does not find his arguments convincing.  We need to move on.
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h.a.c. van asten

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Re: Why 10AM from Lae?
« Reply #24 on: May 31, 2011, 12:53:51 PM »

G.Lapk. Yes , but my question was : why would the navigator succesfully establish position by a sunset running fix , whereas 10 1/2 hours later , with only the sun available , he would at random fly to destination , RDF failing , without an as good as possible sunrise position check before going inbound ?

I btw herewith leave this forum , I find the reactions , mostly upon questions of others I have replied to , too hostile to continue contributions.
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Alex Fox

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Re: Why 10AM from Lae?
« Reply #25 on: May 31, 2011, 03:34:03 PM »

I found the exchange to be enlightening and incredibly civil.  I don't see anything that could even be misconstrued as hostile.  Unless bolding text is the navigational equivalent of cursing at someone.

Anyway, this is way out of my league in every academic sense, but I still find it very interesting.
#4317
 
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h.a.c. van asten

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Re: Why 10AM from Lae?
« Reply #26 on: June 01, 2011, 02:07:45 AM »

G.Lapk. You discard the possibility that Noonan established position by a sunrise/sunset fix as in EJN-208/2011,using the sextant for observation. To my surprise however , you published in NavList "Longitude by Sunrise" , Feb 05-2010 , that you have used the methodology yourself with very good results (0.1 nm) , using the U.L.sun. You did not observe from o/b of an A/c evidently , but the very same fashion was succesfully used from aloft by mrs.C.Lindbergh (LA to NY , 1930) ,Getty (1931) and Ellsworth crossing Antarctica (1935) and F.Chichester for finding the small islands Norfolk and Lord Howe in the Tasman Sea (1932). Did the radio communications stop after 2014 GMT because Amelia Earhart needed time to knock Noonan cold for punishing  hiim since he had slept during the entire journey ?
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Ric Gillespie

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Re: Why 10AM from Lae?
« Reply #27 on: June 01, 2011, 06:39:38 AM »


I thought you were leaving.

Did the radio communications stop after 2014 GMT because Amelia Earhart needed time to knock Noonan cold for punishing  hiim since he had slept during the entire journey ?

What makes you think that radio communications stopped after 2014 GMT?
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Gary LaPook

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Re: Why 10AM from Lae?
« Reply #28 on: June 01, 2011, 06:51:48 AM »

G.Lapk. You discard the possibility that Noonan established position by a sunrise/sunset fix as in EJN-208/2011,using the sextant for observation. To my surprise however , you published in NavList "Longitude by Sunrise" , Feb 05-2010 , that you have used the methodology yourself with very good results (0.1 nm) , using the U.L.sun. You did not observe from o/b of an A/c evidently , but the very same fashion was succesfully used from aloft by mrs.C.Lindbergh (LA to NY , 1930) ,Getty (1931) and Ellsworth crossing Antarctica (1935) and F.Chichester for finding the small islands Norfolk and Lord Howe in the Tasman Sea (1932). Did the radio communications stop after 2014 GMT because Amelia Earhart needed time to knock Noonan cold for punishing  hiim since he had slept during the entire journey ?

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My post was the 14th post on a thread started by a professional shipboard navigator who was
criticizing an article in Ocean Navigator Magazine entitle  “Longitude by Sunrise” which is why
the thread had that name, I wouldn’t have used that title.

See the first post here:

http://www.fer3.com/arc/m2.aspx?i=111750&y=201002

Nine people posted to this thread and if you read them all you will find disapproval of the
method and caveats about its lack of  accuracy. It was generally agreed that due to the inherent
inaccuracy in the method that it might be useful as an emergency, or lifeboat method.

Here is the link to my post that you mis-characterize as my determining longitude.

http://www.fer3.com/arc/m2.aspx?i=111795&y=201002

If you reread it you will see that it discusses the derivation of normal lines of position from zero
altitude sights taken on a ship with accurate heights of eye (24 and 26 feet) and special
corrections for non-standard temperature and pressure. Here is the first paragraph:

“Zero altitude sights (Hs = 0) can work out well but the problem is that
you don't know if this sight is an accurate one or an inaccurate one due
to the vagaries of refraction that the observer won't know about.
Because of this you have to allow a larger uncertainty band around any
LOP taken this way. I have taken such observations in flight and they
work out well considering the lower accuracy inherent in flight
navigation and I have carried a table in my wallet for 30 years for this
purpose, it is posted here:”

You do see the mention of “LOP” in the paragraph and the word “longitude” does not appear in
my post.  You cite one observation that resulted in a 0.1 NM error in the derived LOP but you
left out the other two observations that had errors of 1.8 and 2.3 NM. I never got this level of
accuracy for zero altitude LOP observations from an airplane, they were usually in the 10 to 20
NM range, and, in case you missed this point, these were normal LOP observations, not
observations for longitude. I would not have been able to achieve even this level of accuracy
without the modern refraction and dip tables applicable to airplanes that were not available until
1951.

 I ended the post with:

“These all provide useful LOPs  keeping in mind the larger band of
uncertainty.”

You should read the rest of the posts on that thread and you will see that the other guys got worse
results.
See: http://www.fer3.com/arc/sort2.aspx?y=201002su




You should read my other two posts on this thread in which I lay out all the problems with the
inherent inaccuracy in these types of sights for LOPs.

http://www.fer3.com/arc/m2.aspx?i=111779&y=201002

http://www.fer3.com/arc/m2.aspx?i=111780&y=201002



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). 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, 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.

Gary LaPook
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Gary LaPook

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Re: Why 10AM from Lae?
« Reply #29 on: June 01, 2011, 07:06:13 AM »

G.Lapk. You discard the possibility that Noonan established position by a sunrise/sunset fix as in EJN-208/2011,using the sextant for observation. To my surprise however , you published in NavList "Longitude by Sunrise" , Feb 05-2010 , that you have used the methodology yourself with very good results (0.1 nm) , using the U.L.sun. You did not observe from o/b of an A/c evidently , but the very same fashion was succesfully used from aloft by mrs.C.Lindbergh (LA to NY , 1930) ,Getty (1931) and Ellsworth crossing Antarctica (1935) and F.Chichester for finding the small islands Norfolk and Lord Howe in the Tasman Sea (1932). Did the radio communications stop after 2014 GMT because Amelia Earhart needed time to knock Noonan cold for punishing  hiim since he had slept during the entire journey ?
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Further response:

Here is what I posted about the article in Ocean Navigator Magazine about that author's idea that a navigator could use the van Austen method of using a sunrise/sunset observation should be used to determine longitude:

"I always start with the proposition that you always know where your are, e.g. on the planet earth, in the middle of the ocean, etc. The real question is "do you know where you are to the precision needed at the time?" If you are in the middle of the ocean it may be sufficient to know only that you are "in the middle of the ocean." As you approach dangers then the needed level of precision increases to the point that you need to know where you are to within a few meters when entering a pass through a reef  at night. The position finding system basically utilizes additional information, as it becomes available, to increase the level of precision and thereby refine the position. Based on this, this method does add information and so improves the precision of the position. In some places it may provide the level of precision necessary but in others it can't. In the middle of the ocean it is adequate but nearing a hostile shore it isn't.

Looking at specifics. First, it states to use the lower limb when timing sunset when the table itself says to use the upper limb for this measurement. This may be just a typo. This error would make at least a 32' error in longitude.

The sunrise- sunset table only tabulates the times to the nearest whole minute meaning that the actual event could occur thirty seconds earlier or later. This would cause an error band 15' wide on the calculated longitude.

The times are tabulated for a three day period based on the middle day so have a built in inaccuracy for the other days. Just glancing at a random page in the table and comparing times on consecutive pages I found, at high latitudes, a change of 15 minutes in the three day period and even at 60° latitude a change of 8 minutes. There are probably larger changes than these on other pages. So using the tabulated times for the two days other than the middle day of the period it is quite likely to introduce a two minute of time error adding an additional 30' error in the calculated longitude. At 72° latitude this error could be, or exceed, 5 minutes causing a 75' error in the derived longitude.

The computation requires you to know your latitude to use to enter the table. The table is, in essence, a tabulation of the traditional "time sight." If you are not at one of the tabulated latitudes straight line interpolation between the tabulated values will also introduce an additional error since the time of sunrise and sunset doesn't vary this way but I haven't attempted to quantify the error introduced this way, but it is larger than zero.


In addition to these errors inherent in this method there are also the errors in the observation of the upper limb on the horizon, dip and non standard refraction. Looking at the refraction correction table in the N.A. shows up to a plus and minus error of 6.9' for non standard conditions which introduces a possible additional error band in the LOP of 13.8'. And in some instances the error could be much worse but far from land you will not see the resulting mirages that could tip you off if land were nearby. The error introduced in the derived longitude due to errors in the refraction correction (and dip, if not allowed for) can be much larger than the actual error itself. Except on two days of the year the actual LOP doesn't run directly north and south but is at right angles to the azimuth of the sun which varies with latitude and declination as is clear from an examination of Table 27 in Bowditch, Amplitudes. Because the errors in observation act at right angles to the LOP (along the azimuth to the sun) the error in the derived longitude will exceed the magnitude of these errors, increasing as the azimuth of the sun varies from straight east or west ( the amplitude) which at 60° latitude, for example, is 52.9°. For this case the error in longitude will be 66% larger than the error in the observation itself so the error band in the longitude from non-standard refraction (not counting extreme, mirage, conditions) increases from 13.8 minutes to 22.9'.

But, since to do this computation you must have the Nautical Almanac, why not just work the sight as a normal LOP with a sextant altitude of zero degrees? This eliminates the timing problems and the multiplication effect on the errors in the observation?"

To which I added:

I had written:

"The computation requires you to know your latitude to use to enter the table. The table is, in essence, a tabulation of the traditional "time sight." If you are not at one of the tabulated latitudes straight line interpolation between the tabulated values will also introduce an additional error since the time of sunrise and sunset doesn't vary this way but I haven't attempted to quantify the error introduced this way, but it is larger than zero."

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I decided to do a trial computation to look at this factor. Using today's data, the time of sunset at 30 ° latitude is 14 minutes, 10 seconds earlier than at 20°. Using straight line interpolation for 25° latitude, as stated in the article, sunset should be 7 minutes and 5 seconds earlier but, in fact, it is 7 minutes and 24 seconds earlier, a difference of 19 seconds. So using straight line interpolation would cause an error of almost 5' in longitude. It is certain that there must be even larger differences for other dates and   latitudes and, therefor, larger longitude errors if using this method.

Gary LaPook

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