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    Re: Need Help w/ Ageton method...
    From: Phil Guerra
    Date: 2003 Mar 3, 20:14 -0600
    Message
    You know, after I sent the message to the group, I read through most of the
    posts, until I found a clue.  Someone was looking for formula derivations,
    and actually posted the formula used to calculate the A value.
    A = log(csc(angle)) * 100,000

    In his examples on Solving Great Circle Sailing, he gives a very terse explanation, that I'm sure was sufficient if you were taking navigation classes, with an instructor to expand the method's procedure.  Only 1 example was given for using the solution procedure.  In the example, he mentions taking the B function of R and use it to calculate the azimuth.  Only he never gives how you get the B function of R.  You really wouldn't need the arc value of R, but there is no explanation of how to look it up. There is a formula, but this seemed odd to me to have to solve, it's a trig formula, that I don't think you can solve very easily without consulting other tables, or use a modern calculator.  So, I was a bit lost.  There must be a way to derive the function value from the existing Ageton book, or you would need another set of books with trig tables and logs.   Of course, it didn't help that the formula did not give the derivation of the A or B values in an obvious way.  Still the pleasure in all of this for me is the puzzle of unlocking keys to it and solving it.   It is a magical experience to learn a method that's over 60 years old, and be able to decipher.  After having understood and actually solved a problem with his method, it's a shame that new methods and tools have placed it so far back that it is danger of being lost.

    Anyway, reading the post, seemingly unrelated,  gave me the clue I needed to get the answer, your response, along with others received this morning confirmed it for me.  Now, if I could understand how the table I values are derived, I'd really be smokin'. 
     
    I really appreciate the way this group takes time to answer even newbies.  I don't have any experience with going to sea.  I am handicapped, but have really gotten into the subject of Celestial Navigation for the beauty of the methods.  I wish I could sometime go to sea, but I'll push forward in my studies, anyway. 

     Again, thanks for the help.


    Phil
    Wishing for the wind on the water...
    ----- Original Message -----
    Sent: Monday, March 03, 2003 2:57 PM
    Subject: Re: Need Help w/ Ageton method...

    I don't have my Ageton book in front of me (is it Pub 211? or 213?) because I am traveling, but I think I remember the terminology.  This is my favorite sight reduction method and I use it a lot.
     
    R is the "artificial" arc that is dropped from the celestial body to intersect as a perpendicular the co-latitude of the observer.  Ageton, like many others, decided to solve the oblique navigational triangle by dividing it into two right-angled spherical triangles with this perpendicular.  (Others dropped perpendiculars from different points as well.)
     
    You don't actually need to write down R to solve for intercept or azimuth, just look it up in the tables from its A value and then immediately write down its B value.  As you probably know, this B value is a log secant (the A value is a log cosecant) multiplied by 100,000.  The B value for arc R is then added to the A value from declination of the celestial body.  This sum gives you a new A value that you look up in the tables and right down as K.  And the rest just follows the rules ...
     
    Hope this helps.
     
    Regards,
    Bill Allen
    -----Original Message-----
    From: Navigation Mailing List [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM] On Behalf Of HGWorks - Phil Guerra
    Sent: Sunday, March 02, 2003 7:18 PM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Need Help w/ Ageton method...

    Is anyone willing to help a newbee with the Ageton method?  I found a copy of Ageton's Celestial Navigation, copyrighted 1943.  I've gone through the example in the back chapter on using the method with D.R., but I don't understand where he gets the value 'R'.  I can see how he draws the line segment, but where is that value taken from the table, or is it derived from a formula only?
     
    Thanks
       
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