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Author
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Topic: Problem taking first sighting w/ artificial horizon
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vandy
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posted August 22, 2014 05:55 PM
Hey Everyone,
I'm just getting started in celestial navigation so please be patient with my classic beginner question.
I bought a Davis artificial horizon and a mark3 plastic sextant along with Starpath's Cel Nav book.
Today I tried to take my first sighting and failed big time! ;-)
The good news. I can set up the AH. I can find the sun in the water. I can adjust my sextant and bring the sun into coincidence.
Here's my problem. My sightings are WAY off. I took one of the Sun when it's actual elevation was 25.84 degrees at 9:05 this morning. My sextant however read 91 18". Half of that is 45 48". WAY off.
Are there rules on how much water should be in the tray? Rules on height of AH or distance one should stand from the AH that I don't know about? Rules on angle of my line of sight to the water in the tray?
Thoughts, ideas?
Thanks!
From: United States
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Capt Steve Miller
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posted August 23, 2014 06:12 AM
There is no rules on how much liquid should be in the AH tray - just make sure the bottom of the tray is covered so you have a clear surface.
There is no specific height to have the AH, personally I set the AH on the ground, others set the AH on a stool or table. Use what ever height is comfortable.
The distance one stands is dependent on being able to see the object (i.e. Sun) in the AH. Moving your position closer or farther away will accomplish that.
If you are doing a sight and do know the actual altitude of the Body, you can double that angle and preset the sextant to that angle and do the sight. You should have to make only minor adjustments on the sextant to get your sight.
As to why you were so far off almost double it is hard to say without seeing your setup and watching you do the sight.
From: Starpath
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vandy
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posted August 23, 2014 07:51 AM
Thank you Capt Miller!
Went outside this morning with Sun elevations for my location over the span of an hour. This helped me find the problem. Yesterday I was basically standing over the AH and looking down into it. This was confusing to me because you can see a reflection of the sun at that angle.
Today I raised the AH up on a table and brought my eye closer to the same plain as the AH. What do you know? I found the sun there as well. A quick check from the numbers I brought showed me I was now using the AH correctly.
I then took some sightings of my own...came back inside and ran the numbers.
This time I was only about 3 miles off of my actual location.
Redemption!
From: United States
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