NavList:

I have been going through a celestial workbook, and was reviewing the advanced LOP.  I tried making a hypothetical extension to the problem in the book.  When I completed it, the results did not add up...and I realize that I have some sort of logic error in my thinking about advancing LOPs.  Please look at the attached PDF file.

The graphic conventions are that LOPs have arrows on either end; azimuths have arrows on one end; all times are in GMT.

Page 1:  One sun sight in the morning, and one in the afternoon.  We advance the morning sight.  We get a running fix.  No problem.

Page 2:  For the purposes of this PDF file, I presuppose that Venus is particularly bright and my sextant telescope is particularly powerful.  Hence, I am able to take a daytime sight of Venus.  The results I get from my Venus sight enhance my Sun LOP, and I end up with a celestial fix.  No problem. 

Page 3:  It seems like it ought not matter whether I advance the morning sun sight or the morning Venus sight.  Advancing an LOP should work the same, no matter which one I choose...or so it seems to me.

HOWEVER, my advanced Venus LOP does not cross my 2107 Sun LOP in the same place that the advanced sun sight does.  The running fix using the Venus sight is several miles west of where the running fix using the morning Sun sight is..

Once I noticed this, I was able to reproduce it with other running fix scenarios.  For instance, if I take a pre-dawn sight of Aldebaran and Venus, I get a fix.  I take a noon sun sight, and I should be able to advance EITHER the Aldebaran LOP or the Venus LOP, and I suppose that I should get the same location for my running fix...except that I do not, or at least not when I have worked it out this weekend.

The only good news here is that whatever flaw there is in my thinking, it is consistent.  Everything I do with these running fix scenarios is wrong.  I would be grateful if you could point out to me where I am wrong.

Thanks so much!

Bob