NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Mr. van Asten
From: Gary LaPook
Date: 2013 May 1, 23:27 -0700
From: Gary LaPook
Date: 2013 May 1, 23:27 -0700
| Oh really? You made a 300 nautical mile error and you even admitted it at the end of this exchange. (van Asten's are in red and mine in blue) Mr.Lapook , You write " We will start with his idea that Noonan measured the point of "van Asten sunrise" with a marine sextant .." mr.Noonan´s assumed observation error did not occur due to using the mariner´s sextant , but on the contrary : it occurred by not using the bubble sextant like @ sunset. At best the m-sextant delivered an easy means of establishing A/c´s exact altitude above ocean´s surface (via the dip table of H.O.no.208) , whereas also the dark green filter was a feature . Sunrise point of time could be established by observing with the unarmed eye (but : see filter) , with a telescope , binoculars , etc. since sunrise time is not a measurement , it is an observation only to match time with the preomputed running fix graph , or time-position group listing . Also the short period between 071930 GMT sunset & the 0720 position report delivers proof that a running fix table , or graph , had been precomputed. The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given. ------------------------------------------------------------------------- « Reply #188 on: June 13, 2011, 12:49:03 AM » Mr. van Asten, Your diagram in your article shows that they reached the turnoff point at 1859 GMT at which point the sun's altitude was 16° 04.5' (not the 21 ° that you stated) for an observer at Howland and anywhere else on the correct LOP through Howland. This was plenty high enough for accurate sextant sights. ---------------------------------------- « Reply #190 on: June 13, 2011, 03:38:05 AM » You may safely assume that in the course of 23 years I have consulted all representative flght manuals . When commencing the 055 T offset @ 1815 for the correct longitude sun´s altitude was 04-26 , at the end @ 1859 it was 21-00 . On the erroneous offset the respective elevations were 04-21 and 16-00 , all figures rounded to arcmin. I already mentioned by comment that the 16-00 / 21-00 difference may be a weakness of determination , also since textbooks prescriptions ask for repeated observation like you say . Because for the article I had to do the work alone (no old style navigators available , no readers) , and against deadlines , combined with the menace of making the treatise unreadable due to too many details , I decided for the text & diagrams as published . I have worked for 20 years in the sciences during my professional career , there is not any reason for which I would venture to " wiggle out" (as you call it) from a problem . There is namely , a possibility (not yet computed) that the offset entire track was longer than 132 mls because instead of having made good 348 mls @ 175453 GMT , only 337 mls had been made good , this has influence on the ETA time-position groups . ---------------------------------------------------- « Reply #199 on: June 13, 2011, 12:03:50 PM » ----------------------------------------------------- Mr. van Asten, If there really was a difference between the 16 degree altitude of the sun at the erroneous interception that you claim compared to the 21 degree altitude that you calculate for the correct LOP then the difference between them, 5 degrees, would produce an error of 300 NM, pretty hard for Noonan to be that wrong! AS I posted before, the correct altitude at the turn off point onto the correct LOP was 16° 04.5' at 1859 GMT. There is something wrong with your computations of these altitudes. Here is link to the U.S. Naval Observatory site that will do the computations for you so you won't get the wrong answers. http://aa.usno.navy.mil/data/docs/celnavtable.php Readers of these posts can go to that site themselves and check Mr. van Asten's computations themselves. Just put in the date, time, and the coordinates for Howland (0° 48' N, 176° 38' W) to calculate the sun's altitude at Howland and any place along the correct LOP through Howland. Look at the column marked "Hc" which is the standard abbreviation for "computed altitude." "Zn" = azimuth and "GHA is Greenwich Hour Angle. While you are at it you can check out Mr. van Asten's calculation of GHA of the sun for 175453 GMT, just enter in that time and look at the GHA column. Mr. van Asten said in his prior posts that the GHA of the sun at that time was 88° 43.2', did he get it right? I said the GHA at 175453 GMT was 87° 45.7', did I get it right? And no, I do not assume that you have consulted all representative flght manuals since you have failed to cite to any of them in your posts or in our other correspondence. ----------------------------------------- « Reply #203 on: June 13, 2011, 02:47:02 PM » Mr. van Asten, Using your coordinates for what you believe was the correct turn off point at 1859 GMT produces an altitude for the sun of 16° 00.8' so it was not the correct turn off point because the altitude is not equal to the altitude at Howland for the same time which was 16° 04.5'. and this is the essential requirement for the LOP. However, I see that the altitude at the erroneous coordinates used by Williams, 0° 49' N, 176° 43' W produces an altitude of 16° 00.3' so your turn off coordinates are within half a mile of the LOP through the Williams coordinates so this is accurate enough. The difference between the altitudes at the Williams coordinates and the correct coordinates for Howland would have caused the LOP through the Williams coordinates to be parallel to the correct LOP and offset by 4.2 nautical miles, not enough to cause them to miss the island. Notice, none of these altitudes are anywhere near the 21 degrees that you claimed. The altitude of the sun at 1859 at the point you identify as the erroneous turn off point was 15° 52.2' a difference of 8.1 nautical miles from your correct turn off point onto the Williams LOP and 12.3 NM short of the actual LOP through Howland. I can't believe that you didn't notice your error in claiming that the altitudes were 16 and 21 degrees, a difference of 5 degrees, since THE BASIC PREMISE behind all celestial navigation is that a difference of 1 degree produces an error, or difference, of 60 nautical miles. Your calculated altitudes produced an error of 300 NM! Tsk, tsk. Such an obvious error calls into question all of your other calculations. ------------------------------------ « Reply #204 on: June 13, 2011, 03:04:07 PM » Yes I made some arithmatic error somewhere here , but not in the other calculations . See corrections posted (diff. error vs correct -28´) --- On Wed, 5/1/13, h.a.c. van Asten <hac.vanasten@gmail.com> wrote:
|
