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» Online Classroom   »   » Public Discussion of Cel Nav   » Lunars, how sensitive for the heights and how to find heights. (Page 2)

 
This topic comprises 2 pages: 1  2 
 
Author Topic: Lunars, how sensitive for the heights and how to find heights.
navi


 - posted December 09, 2017 10:00 AM      Profile for navi           Edit/Delete Post 
HI again,

So I did NOA sight reductions and got almost exactly the same erronous data as with 249! I must do the same error with the forms in both cases.

(I am surpised since I went through the whole Celestial Navigation course book with very consitent and results using 249.)

Finally I did also direct calculations as desvcribed on pages 119-120 in your book and got the CORRECT Hc!

From: Chi
David Burch


 - posted December 09, 2017 10:25 AM      Profile for David Burch           Edit/Delete Post 
I believe that the celestial tools will show step by step what you should have in the form on every line using *both* 249 and NAO tables. That might tract down the issue.

also in passing, 249 could be off by as much as 0.4' compared to calculated or 229 solution.

note this assumes you enter the correct dec and GHA. some programs also compute the NA data, and that can also introduce a tenth or two. but with identical dec and GHA data 249 and NAO could be off as much as 0.4' as it rounds to nearest minute.

PS. I respect the fact that you want to ultimately do all by hand and books. That is a worthy goal. In this case, then, we just use the computers to help track down errors. we let the computer programs grade our work.

From: Starpath, Seattle, WA
navi


 - posted December 09, 2017 05:49 PM      Profile for navi           Edit/Delete Post 
Hi David,

Thanks for clarification Hs and Hc!

By the way UTC is 034332 (not 034322). You used the righ thing first time.

I can live with a few tenths in difference for the heigts between 229, 249, and NOA it should not give a lot of difference in UTC

I will go through it all again tomorrow Sunday. Since I get the same error with 249, and NOA I think I must be doing something wrong at the start, i.e. before going into the tables. (It is very frustrating, I tear my hair of soon, but I WILL get there.)

I will look more into your trouble shooting Excel.

The goal is UTC accuracy using only sextant, tables, pen, and paper.

From: Chi
David Burch


 - posted December 09, 2017 07:51 PM      Profile for David Burch           Edit/Delete Post 
Because of the confusing terminology, I might clarify that "Celestial Tools" is not an Excel sheet. There are such things that do lunars as well. Google "Navigation spread sheets."

celestial tools by Stan Klein is a stand alone PC program.

But to add a layer of complexity, Steve Miller does have a spread sheet for lunars using Stark Tables. Called the Miller-Stark form. This can be printed and used as a pure paper form, or opened in Excel to have it do some arithmetic for you.

I believe Steve is working on an update to his lunar spread sheet that should help clarify the Hs vs. Hc issue. The confusion is you can use either in this process.

Note that his sheet is not related at all to the very helpful set of "navigation spread sheets" mentioned above.

From: Starpath, Seattle, WA
navi


 - posted December 10, 2017 07:06 AM      Profile for navi           Edit/Delete Post 
David,

Thanks for your clarifications. I just used the spreadsheets you provided. And to my GREAT surprise I get the SAME erronous results in the spread sheets both for NOA, 229,and 249! However the Law of cosines give the CORRECT result which is also the same as I get when I do Law of cposines myself.

I can also send the Excel which gives those results to you if you give me an email address.

This is a mystery to me since the input is the SAME for all calculations in that spreadsheet. Why would NOA, 229, and 249 all be the same an incorrect and the law of cosines be correct!?!

From: Chi
navi


 - posted December 10, 2017 07:30 AM      Profile for navi           Edit/Delete Post 
Hi again,

To verify I used the spreadsheet with NOA, 229, 249 and law of cosines on the 7.4 in your book on celestial navigation page 86.

The correct answer in your book is 30d 36.9'

The spread sheet gives:
vol 229: 30d 36.4'
vol 249: 30d 36'
NOA: 30d 36'
Law of cosines: 30d 31.9'

So once again the tables are close an the law of cosines out.

The more I dig in to this the more confusing it gets.

From: Chi
David Burch


 - posted December 10, 2017 08:27 AM      Profile for David Burch           Edit/Delete Post 
This confusion can be resolved. There is some mistake being made. most likely with application of the law of cosines... which is after all what they are all solving.

I am sorry to say this again, but please use starpath.com/calc to get the precise answer, ie to a couple decimals. then check your application of the trig formula.

http://www.starpath.com/calc/Celestial%20Navigation/srt1-2.html

I think we should postpone further discussion of this until you can do that.

All of the answers you listed are the same, except the last one. they differ only in the level of precision, which is in each case in keeping with what the tables offer.

229 is ± 0.1' the others are ±1' the trig solution could be as many decimals as you like, but does not make sense to go beyond 0.1 because the input data are not any more accurate.

So we are looking for this response:

I ran the link above and i get this value xxxxxx which i now know is right and any deviation from that which is not consistent with known available precision has an error in it.

by the way, i think cel tools also shows the "law of cosines" solution because the USPS used to or still does use that.

From: Starpath, Seattle, WA
navi


 - posted December 10, 2017 09:32 AM      Profile for navi           Edit/Delete Post 
David,

I Used the link you just sent and got 37d 31.1' With the Excel you sent the other day 37d 31.1'
With own application of law of cosisne 37d 31.1'
With USNO 37d 31.2'

That is all good. I have no problems with law of cosine in any way shape or form.

But what I repeatidly try to explain is that both when I use the NOA or 249 manually as well as when using the Excel sheet You recommend made by Joseph L Mgguire I get 36d 44' for NOA, 229 and 249 which is different from the correct value. And as I try to say that same Excel gives Law of cosine 37d 1.1' (correct).

1. It is puzzing that the spreadsheet gives different answers between law of cosine and tables

2. That the answer in McGuires Excel for tables is the same (36d 44') as what I get using table by hand.

3. That I succesfully have used 249, and a few times NOA for ALL the excercises in your book with correct results. But that that I cannot get the correct results now.




From: Chi
David Burch


 - posted December 10, 2017 12:22 PM      Profile for David Burch           Edit/Delete Post 
I do not recognize the name Joseph L Mgguire. as i recall the author of the spread sheets i refer to is not listed.

the ones i recommended are at

http://www.navigation-spreadsheets.com/

the author is not the person you cite.

Also please recall the very basic point of cel nav sight reduction. When you compute the HC using calculator or computer or spread sheet, you are using the exact DR position and you get out HC from that position.

Wheres when you use tables such as 249 or NAO you CANNOT use that position and have to choose an assumed position. The Hc you get from that is not expected to agree with what you get from the DR position. You are now looking at the Hc from the AP.

If you want to see The AP answer come out of a computer, then you must input the AP to the computer that you used for the tables, and not the DR. Is this perhaps the issue that is holding things up?

May I ask if you have taken our online cel nav course? The lunar solutions are advanced procedures in cel nav, and there will be many stumbles along the way until the basics are in place.

From: Starpath, Seattle, WA
navi


 - posted December 10, 2017 02:19 PM      Profile for navi           Edit/Delete Post 
Hi David,

I must havs rear your mind. I took a long walk to clear my mind and yes the problem is obvious, I use my Exact position (DR) in Chicago when using law of cosines. When using tables I must chose assumed position AP different from DR to get whole GHA degrees! According to the instructions in your book! Then Hc is different!

This IS the problem! Yes! The obvious is sometimes hard to see.

In practice on the sea this will not occur since I can measure the heights with the sextant!

I can correctly get geocentric LD's at whole hours from Starks book using your work forms.
So:
On land I will use Law of cosine for heights + wwr and www
On the sea I measure heights

I have gone through your book on celestiais with all exceecises using 249 and some NOA

Just took my departure towards Hawaii using your other book.

From: Chi
David Burch


 - posted December 10, 2017 06:43 PM      Profile for David Burch           Edit/Delete Post 
Excellent. You will be an expert at cel nav if you work through the Hawaii by Sextant book.

We will close this topic.

From: Starpath, Seattle, WA


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