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    Re: Latitude by Lunar Distance
    From: Wolfgang Köberer
    Date: 2006 Nov 11, 10:13 +0100

    Dear all,

    Frank's up-tempo reaction to me referring to an article describing his new idea 94 years ago, causes me to give some more information:

    The "Annalen der Hydrography und Maritimen Meteorologie" were the monthly journal of the "Deutsche Seewarte", published between 1872 and 1944. During the period of interest here, prior to the "Great War" (as I think they say in your part of "Old Europe", George) it contained articles and reports on hydrographic subjects (ocean drifts and water depths etc.) as well as on weather forecasting - some colorful descriptions of storms in the North Sea area - and, of course, celestial navigation. The articles on celnav did not make  up the bulk of the contributions, as the intercept method had been almost universally adopted in Germany. Those articles were mostly concerned with refining measurement - I recall lengthy reports on dip experiments developing formulae - but some treated celestial navigation in the air (mostly for the benefit of determination of the position of a balloon) and therefore without a usable horizon. There were also discussions about new tables or graphical means of shortening the necessary calculations.

    The article by Jäger proposes - as the title says - to find one's position by determining the parallax of the moon. The explanation is about the same as given by Frank - and it does not contain a worked example. The article also discusses the shortcomings of this method: an error of one arc second leads to an error in position of one nm at best. In our latitudes the error may amount to as much as 40 nm - due to the fact that the moon is not as high in the sky - on the condition that sextant reading is accurate to 10 arc seconds (which is the smallest division of the scale of the Plath Navistar Professional for instance - and Plath only guarantees an accuracy of +/- 20 arc seconds). Best results can be obtained when the moon is near culmination and when the star observed is above or almost above it. When taking the distance to a second star the second star  distance should form a right angle with the first (which is self explanatory) and this may be a rare condition.
     
    Jäger mentions that he has tested the method on board of "Herzogin Sophie Charlotte" himself - it is interesting, though,  that he does not say that these test were satisfactory, as one would expect if they were. There was no reaction or discussion of the method in the "Annalen" afterwards; it obviously sank like a "lead duck" as we say in this country - only to be discovered by Frank almost a century later.
     
    If anybody is interested in a scan of the article, as ever: feel free to say so.

    Regards,

    Wolfgang

    -----Ursprüngliche Nachricht-----
    Von: NavList@fer3.com [
    mailto:NavList@fer3.com]Im
    Auftrag von Peter Fogg
    Gesendet: Samstag, 11. November 2006 01:23
    An: NavList@fer3.com
    Betreff: [NavList 1663] Re: Latitude by Lunar Distance



     Frank wrote:
    >
    > I think [position via moon parallax is]
    > quite a novel concept for this group of people. I suppose that's why a
    > couple of people were determined to attack it instead of trying it out.

    Having followed this topic with some interest, as was also shown by
    others, I don't recall 'attacks' as such. What I do remember are
    requests for more detailed information, and perhaps the expression of
    a little frustration when this was not forthcoming. Don't be so quick
    to assume the mantle of the martyr, Frank. Do feel encouraged to
    explain fully new concepts.

    The other interesting aspect here is that we now know this idea was
    described in 1912...how?

    Because it was published in a peer-reviewed journal and has thus
    endured 94 years so far. I seem to remember some pooh-poohing of this
    suggestion when proposed as appropriate for Frank. Perhaps the value
    of publication in such journals has been supported by this revelation.

    The advantage of peer review before publication is that the process
    (should) ensure that the idea is complete (whole), is well expressed,
    and (hopefully) able to be demonstrated. It makes a good idea better,
    while weeding out the others.

    Which brings us full circle to the shortcomings of the expression of
    this idea as presented.

    100% for ingenuity, Frank; but only 30% for clear expression.


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