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» Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » Artificial Horizon

Author Topic: Artificial Horizon

 - posted September 10, 2011 03:15 PM      Profile for Tedder           Edit/Delete Post 
Using a Badar solar filter, I have learned how to find the Index Error of my Davis Mark 15 plastic sextant and adjust the horizon mirror.

However, when I go to take a sun sight, now I cannot find the Davis Artificial Horizon reflected sun in my sighting telescope. I can move the sextant to my right and find the Horizon's sun, but I lose the sextant's sun. With me standing about six feet away from the AH, it seems that the sextant sun is several inches or so to the left of the AH. I cannot bring them together, so I cannot take a sight.

I suspect side error is the culprit, but I am not sure. I use two nuts to adjust the index mirror as I have no dice, and I believe the adjustment is correct--or at least the best I can do.

Any ideas to solve this problem?

From: Apalachicola, FL
Capt Steve Miller

 - posted September 10, 2011 04:40 PM      Profile for Capt Steve Miller           Edit/Delete Post 
If you are using the Davis Artificial Horizon, I would recommend using the 'blue' and 'clear' plastic plates. This does provide some protection for your eyes from the brightness of the Sun.
The first step in using the AH is to start with simply stand at the appropriate distance away from the AH so that you can see the reflected Sun comfortably in the AH (it does not matter which side you look through blue or clear) - not contorting your body to see it. Then place the sextant between your eye and the AH reflected image ensuring that again you can see the reflected image through the sextant.
Next, set the sextant to the approximate Hs and again look through the telescope at the reflected Sun and with proper shades in place. It is likely that you will not see the sextant reflected image of the Sun yet.
To see the sextant reflected Sun in the one of the important actions that must be used with the Artififial Horizon is to not just move the sextant right and left and up and down , BUT to ROTATE the sextant about the axis of the telescope to insure that it is VERTICAL.
With these three motions PLUS rotating the micrometer drum you will find the second (sextant reflected) image visible in the AH as well as the original image. All of this movement is not trivial and it does take practice.
With my sextant I usually see the original AH image as a blue disc (from the blue plate) and my sextant reflected image as either a reddish or oragnge disc.
Once both discs are visible I line up the reddish disc above and just tangent (touching barely) to the blue disc. This orientation gives a lower limb sight.
Hope this helps.

From: Starpath

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