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Author
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Topic: Noon Sights (LAN) with Artificial Horizon
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BSmith
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posted November 05, 2015 06:30 PM
Newbie Question here...
First of all, I'm inland, nowhere close to the ocean and don't have a horizon that's useful (trees). I'm trying to find latitude at LAN with a Mark 15 sextant and an artificial horizon (AH) (tray of water).
I'm working through Ch. 3 of the 2nd Edition of Celestial Navigation Home Study Course, particularly the form on p.41 to find latitude at noon.
I'm assuming that since I don't have an ocean and am using an AH, I skip the 'dip correction' when finding Ha from Hs.
I'm also assuming that since I superimpose the 2 images of the sun on top of each other, I skip the altitude correction step (1-4).
Are my 2 assumptions correct?
I came within 3.8nm of what Google Earth said I should be at.
Thanks,
Brian
From: NY
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BSmith
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posted November 05, 2015 07:20 PM
One more question...
With the AH raw sight, do I take off my IC before or after dividing by 2? (I was thinking before dividing by 2).
Thanks,
Brian
From: NY
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Capt Steve Miller
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posted November 05, 2015 07:58 PM
When you use the Artificial Horizon there is no dip correction as when you divide by 2 you have the Hs above the virtual horizon.
You still need the altitude corrections though. That said you will not need the semi-diameter portion of the correction when doing overlapped images so DO NOT use the corrections for the Sun, instead use the corrections for Stars & Planets. Those corrections account for the Refraction and Parallax. There is a note at the bottom of Table A3 regarding using a Bubble sextant - this note would apply to an Artificial Horizon site when overlapping the images. If you make the images tangent either at the top (lower limb) or at the bottom (Upper Limb) of the image in the A.H. then you would use the normal Sun corrections because then you would be doing an Upper or Lower limb site.
As for applying the IC you do it before dividing by 2 - see the last paragraph in the right column on page 163 in the Cel Nav text.
From: Starpath
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BSmith
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posted November 06, 2015 07:27 PM
Capt Miller
I appreciate your comments as they were extremely helpful. I didn't notice Sec 11.19 on AH in the book as I started reading from the beginning. After adjusting my calculations to include a star altitude correction as you suggested, my error is now down to 1.2nm which I'm quite pleased with as this is my first attempt.
Thanks,
Brian
From: NY
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