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» Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » Lunars, how sensitive for the heights and how to find heights. (Page 1)

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


 - posted December 06, 2017 06:31 PM      Profile for navi           Edit/Delete Post 
Data:
UTC 03h43m32s 6 December 2017
Lat 41d 52.7' N
lon 87d 37.8' W
(Chicago)

Measuring the distance between Betelguese in Orion to the far side of the moon I get sextant distance of 25d 6'

To get the heights I use 2102-D and plot the moon at the time of the measurement ->
GHA moon= 20d 11.1'
Dec 19d 45'
Then SHA moon= GHA moon- GHA aries = 20d 11.1' - 131 d 0.3' = -110 d 49.2' adding 360 I get
249d 10.8'
Then Rim scale on red disc = 360 - 249d 10.8' =
110 49.2' I plot the moon through the slot of the red disc at Dec 19d 45'

I put on the blue template 45N and turn it to LHA aries = GHA aries - DR lon = 130d 60.3'-87d 37.8' = 43d 22.5'

From that I then read height of moon = 26d
height of Betelguese 36d

Using the tables in Starks book I get Ma 25d 7.3'
Sa 36d 1.3'

Furtmermore using stark at
UTC 3 I get LD 24d
UTC 4 I get LD 24d 35.2'

Cleared distance I get 24d 20.4' which give me an UTC of 3h 34m 46s

That is 7m 46s slow.

That is 4.6' error in lunar distance measurment which I think is too high consideriong I use a metal sextant with a 6 magnification scope sitting stable on a chair on land.

Can the error come from me calculating the heights using the 2102-D?

What is the alternative way of getting the heights using the nautical almanac?

From: Chi
Capt Steve Miller


 - posted December 07, 2017 10:55 AM      Profile for Capt Steve Miller           Edit/Delete Post 
First of all the Star Finder is not accurate enough for determining the Hc of the Moon and the other body.
You should do a sight reduction to compute the Hc. This can be done using the work form as usual dealing only with the Hc computation (ignoring the Hs to Hc computations). You would use all the normal inputs.
You could also us a calculator/Computer program to Precompute the body's altitude for the time of your Lunar. This is the method that I use.

Betelgeuse is not a normal star to use for a Lunar - it is not on or near the ecliptic. I ran into the same problem with Sirius.

Your error in Lunar Distance is not due to the sextant you used.

Using 2102-D is part of the problem, using Betelgeuse is another part due to the relative motions of the Moon and Betelgeuse.

You might have had some errors in the Stark solution. I am looking into this as well and will make another post in a while.

From: Starpath
navi


 - posted December 08, 2017 10:03 AM      Profile for navi           Edit/Delete Post 
I will post two pictures of Stark calculations.
The first is based on heights using the graphical solution with the 2102-D, the second using 249.


From: Chi
navi


 - posted December 08, 2017 10:09 AM      Profile for navi           Edit/Delete Post 
This calculation is done with heights using sight reduction with 249.

The result with this is WORSE than using the 2102-D!

You say Betelgeuse is a bad star for this. I get in the geoecentric LD
24d 00.0' at UTC3 Dec 6
24d 35.2' at UTC4 Dec 6.
(Sextant distance is 25d 6.0' at 034332 Dec 6
(Sextant distance is 38d 35' at 034332 Dec 7
Wouldn't that suggest the movement is good?

Where do you think the error is from?!



From: Chi
Capt Steve Miller


 - posted December 08, 2017 12:11 PM      Profile for Capt Steve Miller           Edit/Delete Post 
I have attached my Stark Form using the TI89 calculator and the StarPilot 89 software to determine the altitudes of the Moon (29*48.7') and Betelgeuse (37*04.3')

Note that I got the following:
Ma 28* 57',
Sa 36* 05.6',
UTC 3 LD 24* 03.0',
UTC 4 LD 24* 35.1',
Cleared Distance 24* 26.6',
UTC of 3h 44m 6s,
Calculated Time 34s slow,
8.5' Longitude Error



From: Starpath
navi


 - posted December 08, 2017 01:11 PM      Profile for navi           Edit/Delete Post 
Hi Capten Miller,

The positive things is that my old french sextant must be pretty dang good, and my hands stable! 34 sec and 8.5 miles I am happy about! Shouldn't I be? Time to throw not only the GPS but also the chronometer overboard :-) and due true celestials.

Negative is that I do not get same results as you in the calculations.

Please see below:

Note that I got the following:
Ma 28* 57', I get 21d 18.6' (big difference)
Sa 36* 05.6', I get 36d 5.7' (small difference)
UTC 3 LD 24* 03.0', (I get 24d 0.0' about 10% difference)
UTC 4 LD 24* 35.1',(I get 24 35.2' (small difference)

Cleared Distance 24* 26.6', (I get 24d 13.3 big difference)

UTC of 3h 44m 6s,
Calculated Time 34s slow,
8.5' Longitude Error

Can you please look at my calculated height for the moon (reduction form + how I used wwp and wwr corrections). Calculated heights before corrections are attached here and the wwp and wwr corrections are marked in red in the picture where I clear and get 24 13.3'.




From: Chi
navi


 - posted December 08, 2017 02:07 PM      Profile for navi           Edit/Delete Post 
Please see previous posting as well as these.

I went through it again and I see a few odd things.

First. K for 12d 18.9' in the book gives 1.93911 in your Excelyou get 1.93923 (In my book that is K for 12d 18.8' ) odd! Minor things but still.
(Now I am very close for the geocentrics at 3 and 4 UTC. Within one tenth.)

Then I went through my height calculations again and I get calculated distances closer now (For my moon heights I used the wrong declinations in 249!). But still NOT the same as you!

Hc Betelgeuse 36d 44'
ww ref 1.3'
Sa= 36d 45.3'
You have:
Sa 37* 05.6'

Hc Moon 29d 48'
wwp -56.9'
wwr +1.7'
Ma 29d 6.6'

You have:
Ma 28* 57'

Why do we get different heights?

Please see updated calculation attached here.


From: Chi
David Burch


 - posted December 08, 2017 05:11 PM      Profile for David Burch           Edit/Delete Post 
For any given DR Lat LON, and UTC and body, there is a unique Hc and Zn value.

Please use starpath.com/calc or starpath.com/usno to determine the correct values. This should not be an issue in lunars.

From: Starpath, Seattle, WA
David Burch


 - posted December 08, 2017 05:21 PM      Profile for David Burch           Edit/Delete Post 
I forgot to mention this one, which we recommend in our online course. So if you are making an error in the use of the tables, this will show you right where the error is. Very nice.

_________________

There is an app for PCs written by Stan Klein for the USPS which you can download and install for various computed solutions. See:

http://www.usps.org/eddept/n/tools.htm

It also provides a unique function of telling you what the intermediate step answers should be using various sight reduction methods.

From: Starpath, Seattle, WA
navi


 - posted December 08, 2017 09:17 PM      Profile for navi           Edit/Delete Post 
Hello David,

(I agree the basics from the tables should not get wrong!) I get the LD geocentric at UTC 3 and UTC 4 right. Heights are the problem.

Now I used starpath.com/usno for the Hc's.
In your form you denote the heights Hs and they are NOT the same as Hc I get from the usno. Should Hc be the same as Hs!? If not what is the difference between Hc and Hs?!

Please see attached picture.

Also you use HD 60.9 when I look in my almanac at UTC 03 to UTC 4 my HD are both 60.8.




From: Chi
navi


 - posted December 08, 2017 09:43 PM      Profile for navi           Edit/Delete Post 
Please also see previous reply.

So as mentioned in the previous post I get a discrepancy between usno and what you use. (or should Hc be different from Hs as I ask and what is then the difference.)

I once again went through the form and I get the SAME declinations as usno. But i get DIFFERENT Hc, both different from usno and from your Hs
using 249. Please see attachment.

This is driving me slightly frustrated. Why would Dec be exactky the same but Hc not?!



From: Chi
David Burch


 - posted December 09, 2017 07:47 AM      Profile for David Burch           Edit/Delete Post 
there is just one right answer and the several links given will tell you which one is right. then compare your steps to those to see where the error is.

Use celestial tools to see what each step of the answer is using Pub 249, 229 or any other.

It is far more helpful to you if we guide you to the tools that show you how to find these errors, rather than just track them down individually. celestial tools is your friend.

From: Starpath, Seattle, WA
David Burch


 - posted December 09, 2017 07:53 AM      Profile for David Burch           Edit/Delete Post 
Also of course we must not confuse Hs (a number read from the sextant) with Hc that is a computed Height from known location and time.
From: Starpath, Seattle, WA
navi


 - posted December 09, 2017 08:35 AM      Profile for navi           Edit/Delete Post 
David,

I appreciate your guidance. I have been through the forms many times. I really try to find the errors myself.

I have a few very specific questions that would lead me forward I think:

In your Stark form you put in Hs which in THIS case must be calculated values since I did not made any measurement of the heights. Hence in THIS case is Hs= Hc, is that right or wrong*?

Then I see how you adjust Hs using wwr and wwp from Stark. (I get that part correct.) to get Sa, and Ma.

*What puzzles me is that Hc from usno are NOT the same as the Hs you use in your Stark form!

(I will also now do a sight reduction with NOA and see what I get.)

From: Chi
Capt Steve Miller


 - posted December 09, 2017 09:56 AM      Profile for Capt Steve Miller           Edit/Delete Post 
I should have put Hc in place of Hs on the Stark Form - that is totally my fault. We are calculating Hc (not Hs) and then use the WWP (Wrong Way calculations) and Wwref to take that Hc and convert it to an Hs with corrections for the Lunar.

I did the calculations of the Hc with a few more different calculators and computer and got an Hc for the Moon as 29* 35.4' and for Betelgeuse 37* 01.3.
The computed UTC was 3:43:22 with the time error being 20 sec and the Long Error being 2.5'. (I am not sure why the differences between all the results that I got between devices).

From: Starpath
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


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