NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2012 Oct 18, 18:07 -0400
Hi Lu
Dutton's Navigation & Piloting
Twelfth Edition
Naval Institute Press
Annapolis
1972
PARAGRAPH 2609
quote
A fix is obtained when two or more lines of position are crossed,adjusted to a common time. ... At twilight, in clear weather, he will observe a minimum of five stars, well distributed in azimuth. He will make 3 observations of each body. ... This gives a check on the consistency of observations and therefor their probable reliability.
End quote
The purpose of taking 15 observations of 5 bodies is to provide a more reliable fix, consistent for each body (3 observations), and consistent among bodies (5 stars).
If it was good enough for US Navigational Officers at the height of celestial navigation, then that's good enough for me.
In deference to your considered opinion, you may follow the practice you see fit.
Regards
Brad Morris
I agree that even on land LOPs are likely to be off by a mile or even more and so fixes have that uncertainty; it's just the nature of celestial navigation.
But I have to question the claim that getting three LOPs will give a better fix. As someone pointed out in a discussion on this list a few years ago, there's only a one in eight chance of a fix even being inside the cocked hat and there's no certitude at all that the fix will be in the center of the hat.
From: Brad Morris <bradley.r.morris@gmail.com>
To: NavList@fer3.com
Sent: Thursday, October 18, 2012 12:45 PM
Subject: [NavList] Re: Line of Position Fix
Hi DebraThe best two times of the day are the civil twilights. Those are just before dawn and just after sunset. The best bodies to use are the 57 navigational stars.Just as a note, you will want 3 bodies in your fix. It is unlikely that 2 LOPs will cross at your position, in general, and 3 will produced a 'cocked hat'.Best Regards
Brad MorrisOn Oct 18, 2012 3:23 PM, "Debra Hillman" <wombatroo@hotmail.com> wrote:Could somebody help me with my problem . I am learning on my own at present from books on celestial navigation.I need to get a fix with two lines of position but not sure which celestial body other than the sun and the best times of the day to achieve the fix.
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