NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Latitude by Lunar Distance
From: Frank Reed CT
Date: 2006 Nov 12, 00:21 EST
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From: Frank Reed CT
Date: 2006 Nov 12, 00:21 EST
Alex E wrote:
"However, the most interesting question (on my point of view)
is not discussed.
I mean DOES THIS METHOD REALLY WORK IN PRACTICE ??
(There is no doubt that it is theoretically sound).
And what does it mean that is works.
Can you determine your position with this method
and ordinary sextant
a) to within 1/2 of degree?
b) to within 20 minutes or 1/4 of a degree?"
is not discussed.
I mean DOES THIS METHOD REALLY WORK IN PRACTICE ??
(There is no doubt that it is theoretically sound).
And what does it mean that is works.
Can you determine your position with this method
and ordinary sextant
a) to within 1/2 of degree?
b) to within 20 minutes or 1/4 of a degree?"
Well, I guess it all depends on the meaning of that phrase "ordinary
sextant". <g> Some very ordinary sextants have arc error that would make
them unsuitable unless this arc error has been rather laboriously measured.
Of course, one reasonable way to do that measurement is by shooting lunar
distances. But many ordinary sextants (metal ones only) have insignificant arc
error and are certainly capable of measuring angles again and again to a
couple of tenths of a minute of arc, no doubt about it. I've done it. I've seen
a bunch of people do it in Mystic. By the way, as I mentioned before in this
topic, I'm a big believer in averaging four sights whenever you're trying to do
lunars. And this was considered normal practice historically. That way, assuming
no underlying bias, if I have a typical error of 0.2 minutes of arc in each
observation, the final average angle will be accurate to 0.1 minutes of arc.
And you wrote:
"But my Lunar's results are poor, either because of the
poor sight or for some other reasons, I don't know."
poor sight or for some other reasons, I don't know."
It might be eyesight, but I'm betting on technique (and that sticky
micrometer in your SNO-T sextant). We'll have to talk about technique again
soon. Maybe I can write up my thoughts on the matter early next week.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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