NavList:

   

Reply

Hi.

I have just startet learning celestial navigation, and have bought a
Davis 15 sextant.  Even though it has been rather cloudy here in
Trondheim after I got the sextant, I have managed to get some
"shots".

I am however not satisfied with my results, my observed height is up
to 6.5' different from calculated height.  This is strange as I can
easily notice a 6.5' index error.  And my observed height is always
(with no exceptions yet) less than calculated height.  One would think
that if I am just inaccurate, my results should be on both sides of
the calculated values.  So I am starting to thing I do something
wrong.

Here is what I do, hopefully a kind person reads through it and finds
an error:

I use a Davis artificial horizon with colored glass.

1. First I adjust mirrors.  Horizon mirror is adjusted so that when
   setting sextant to 0 degrees and looking at the sun, both reflected
   and real sun overlaps completely.

2. Then I remove some filters from horizon mirror (could there be some
   refraction here?) and measure height.  Lower limb on sun is taken
   down to touch upper limb of sun's reflection in the artificial
   horizon.

3. I note height, GMT and then check index error with same procedure
   as in 1.

4. Then I calculate, this is an example I took yesterday:

   date:     29/8-2005
   GMT:      13-52-23
   body:     sun, lower limb
   GPS long: E10° 24.7
   GPS lat:  N63° 25.4

   Sextant heigth:  57° 58.4'
   index error:            0'
   halve height:    28° 59.2'
   correction:          14.4'
   observed height: 29° 13.6'

   GHA hour: 14° 47.3'
   GHA inc:  13°  5.8'
   GHA       27° 53.1'
   LHA:      38° 17.8'

   Decl. hour:   N9° 12.4'
   d-correction:      0.8'
   Decl:         N9° 13.2'

   Calculated height: 29° 20.0'
   Height difference:      6.4'



Asbjørn

   

Reply