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Alex,

Thank you so much for doing this.  Your three years of research is
very admirable, in my opinion.  Your findings also dovetail with Jan
Kalivoda's report of the findings of a German who investigated
precision of lunars at sea in the late 1800s.  As I recall, the
standard deviation of lunar distance reported by Jan was about 25
arcseconds.

I am wondering how much practice you estimate it took you to achieve
this level of proficiency?

Thanks,

Fred

On Apr 15, 2007, at 12:59 PM, alex wrote:

>
> What  accuracy can be really achieved with  the lunar method?
> This question was discussed several times, and now I want
> to contribute some data. Let me first cite a great authority,
> Lord Kelvin, then I will post some of my recent observations.
>
> Lord Kelvin says:
> "...to observe the moon's position accurately
> to half a minute of angle.
> This can be done, but this is about the most
> that can be done in the way of accuracy at sea."
>
> And then:
> "If he has extraordinary skill, and has bestowed an extraordinary
> care on his instrument, he may, by repeated observations,
> attain an accuracy equivalent to the determination
> of a single linar distance within a quarter of a minute of
> an angle, and so may find the ships place within seven miles
> of east and west distance; but, practically we cannot expect that the
> ships place
> will be found within less than twenty miles, by the method od Lunars
> in tropical seas
> or within ten miles in latitude 60d;
> and to be able to do even so much as this
> is an accomplishment which not even a good modern navigator,
> now that the habit of taking lunars is so much lost by the use of
> chronometers,
> can be expected to possess.
>
> (Sir William Thomson
> Popular lectures and addresses,
> London, McMillan 1891, vol. 3 Navigational affairs.
> Navigation 1-138 (Lecture delivered in the City Hall,
> Glasgow, Thursday, Nov 11, 1875. Pages 101-102 ).
>
> I also analysed Cook's maps and observations, comparing his Lunar
> determinations
> of the longitudes of known places (those that can be found on
> Terraserver.
> If someone is interested, I can post the results of this analysis.
>
> It is interesting to compare this with my own experience.
> After 3 years of practice, I was able to eliminate the systematic
> errors
> in my SNO-T Lunars, and now I post the data which on my opinion are
> consistent with what Kelvin says (in the next message).
>
> Alex.
>
>
> >



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