Gentlemen,  found  an old 1940 book US Naval Academy,  Plane and Spherical Trigonometry , by Kells, Kern, and Bland.  Admittedly,  majority of the book is trig and exercises, but there are a few spherical trig items which will be helpful if the battery  is dead.  What I personally like about this book, it  does not consider its reader too knowledgable and therefore explains everything to the bone. Which is as a refresher I personally found helpful.  Just for information, of course. ;> ;>

Thank you

All of The Nautical Almanacs have been updated to a better format for viewing.

Improvements are as follows;

- Moon phase graphic
- GHA time separated into 6 hour increments
- Latitude (N or S) provision for each 6 hour increment or when declination changes from N to S.
- Moonrise/set N or S latitude separation
- Sunrise/set N or S latitude separation
- Addition of Equation of Time curve (simple but very handy)

Clear skies,

CelNav57

Bill,

Your video about the Bagnold Sun compass is fascinating!  Your desert attire is perfect!

https://www.youtube.com/watch?v=N-YvH_dUW44

Perhaps because it's so simple to understand....I can't figure it out. 

This much I can figure out-

1- Calculate or use a magnetic compass (adjust for variation) to determine the azimuth of the Sun.

2- Align the index figure (which is the Sun's azimuth) to the shadow cast by the gnomon.  

Here's where I get "lost".  Do I then adjust my course to that the shadow is on, let's say, 270°  ?

Could you help further explain?

Great video! 

Roland

Hello all! 

Great forum here. I've been browsing and learning for a week; as esoteric as it might be these days, it's nice to have a dedicated place for this subject, for people like me that are just learning. 

I have a question I wanted to run by you.  I've done a few manual sight reductions using the tables and a Davis Mark 3 with a bowl of water for an artificial horizon, and been getting LOPs with accuracy within a few miles which I feel is acceptable for a beginner with such a hokey setup ;).  But I've also been using an online sight reduction calculator just to make the practice process faster (yes it's cheating, but who doesn't just want to play with a new toy for a bit?)  I've been using this calculator: 
https://www.celnav.de/sightred.htm

Along with the USNO almanac data.  Seems to work well; again,  LOPs within a few miles.  But I'm curious:  using the tables, it seems (at least with the tables and forms I've been using) necessary to adjust your initial Assumed Position longitude during the conversion to LHA.  This "adjusted" AP longitude is then used in the LOP plotting process.  

So: is it necessary to also adjust the longitude of the Assumed Position when using that online calculator? I'm guessing not, because, well, plotting the LOP using the calculated intercept from the original AP seems to work well, and the calculator doesn't supply a modified AP longitude.  I'm *guessing* that since this is a calculator, it's solving the appropriate formulae using the actual AP, without any modification being driven by the tables. 

Sanity check? Am I right to plot the LOP directly from my original assumed position when using this online calculator? 

Thanks!

Gentlemen.

 just found a small error in 1966 Chapman.  But then found out it was corrected in 1974 ed.  Just for info: 

 Concerning the usage of maneuvering board.  page 430b in 1966 edition. It is an example how to calculate the direction and velocity of the true wind so as to determine whether  you can lay the mark on the next tack and the best course  you will be able  to make  to windward.

Without going into details, let's me just mentioned  from that paragraph "...To solve  for the new tack  we mark the wind  new apparent direction of 169 ( add 17 to 142)  ( this is  math wrong 142 +17=159)  and then add 45 deg on which  you wish to sail.  This gives 204 the new course..." Wind is coming from 125 deg. The boat movement through the water caused the apparent wind to shift 17 deg counter-clockwise from its true direction.Then by mistake just added 17 deg twice.

Chapman 1974 ed. , page  452, corrects the error.  142+45= 187.

Am pretty sure you would not use the wrong approach taking by 1966 ed.   Nothing for granted.   Thank you.

Gentlemen,  below is the translation from German into English of some interesting fact. Hope, you will find it  useful. The translation of the article in the following post was  done by Google, therefore there are quite a few  strange sentences.  But I hope the main content is decipherable.


Magnetic field shiftThe North Pole no longer wanders - it runs
The magnetic field of the earth always seems to be constant. But in truth, it's changing so fast that researchers have to act now.
 
JAN BERNDORFF
[/url]

Hi Shipmates,


I've got some more practice data for you. I've calculated it already; it provides acceptable accuracy:  +- 2 miles

Point one:  For the last month I've allowed my chrono to wander off-time to see where it goes and determine the rate.  I've calculated the error as plus .181 seconds a day.  So taking the daily error into account I had to subtract 7.5 seconds from my observation time.  You must do the same.  So when you average the following sets of observations remember to subtract the watch error.  

Point two:  In my part of the world GMT changed to a new day so please examine the dates carefully... you will have to use a different date for each set of observations.

I made an initial math error of one digit (10 minutes) that threw off my first lops by about 12 miles.  After finding the mistake my lops landed just where they should... My suggestion:  check your figures and math carefully.

Point three:  Remember these observations are in the Eastern Hemisphere and the sun is in the Southern hemisphere.

The earlier observations were taken in clear skies, however, the ones taken later were a bit staggered due to the formation of cumulus clouds which covered about 40 percent of the sky.  The difference in Z is only 30 degrees but that seems enough in this case for a good fix.  Have fun.

Nov 24 GMT

HHMMSS    DDMM.M
233849      2455.6
234027      2516.4
234138      2532.5
234255      2548.0
234405      2603.2

Nov 25 GMT

021451      5337.8
021653      5352.4
021953      5414.0
022044      5421.4
022153      5429.2

eye height = 15 ft
index error = 0
body = sun LL
DR = 10 N  124 E

Here's the GPS location just to see how far you're off: 10:14.54 N   123:57.4 E

Please be advised that this is my last attempt to share my experiences with you...  Most of you haven't the interest to explore this hobby with me, thus, I'm compelled to seek new friends on another board - this one seems practically dead, I'm sorry to say.  In this day and age of the effortless instant email Im much surprised at the lack of interaction.

My sincere respects and appreciation to Capt. Diego Melas for his kindness and generosity.  Diego is a fine Italian man who gave me a perfectly wonderful sextant to enjoy, and who has shared his family and his love of Christ with me and mine.  I now consider him a friend.   

I also thank the few members and ADMIN who have sometimes responded.  For those who wish to communicate with me just send a private message - I will check for mail infrequently but would be happy to correspond with those who have interest.
 
Cheers  

We are all interested in weather - are we not??

So here is some news about fake weather....  read it and weep. However, I whole-heartedly disagree that global warming is man made.... If that were true then there must be man on all the other planets too for they are also warming slightly.

https://www.foxnews.com/science/error-in...pected.amp

Hello!!!

During my home exercises to keep me trained I have encountered some problems in which the result of the value of azimuth is different if calculated with the Eulero's formula or if calculated with the tables ABC

How is it possible?
Can you help me!

One of these act like this:
Dec -14° 39.5'
hc 21° 14.6'
Lat 40N
LHA 315° 5,1'

With the formula:
Z=88°

With ABC tables 
Z=133°

Greetings,

Am pretty sure me only had that kind of a problem in calcs, but, anyway, let me share it with you.  Just in case.

Using intercept method. Getting wrong fixes .  Checked anything a few times, every adding/subtraction.  By the way, I knew what the right fix should be. Just doesn't work. Then recollected oldl engineering rule # 0:  If something is going wrong-check constants.  Anyway, found out that when corrected Declination for proper GMT I added the correction "d" without giving any thought why I am doing it. Just added. In my case it was about 10'.  Then, when I checked NA page and looked down the page, I realized that Decl. is decreasing.  And as soon as I subtracted "d", everything worked fine. Again, I'm sure you know it and pay proper attention to the "tendency" in Decl. to put a correct sign to "d".  Then, when you are using , let say, Pub.229, and correct Hc-then the error in "d" for Decl. does affect Hc.  And eventually intercept itself. 

Never I imagined this kind of error would affect the intercept so much.  In my case it did.

Live and learn. ;> ;>