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    Re: Star-star distances for arc error
    From: Douglas Denny
    Date: 2009 Jul 3, 00:58 -0700

    Excuse me: I did not 'storm off' ! I volutarily disengaged from what appeared 
    to me to be an argument getting out of hand, with one or two overly-sensitive 
    people who do not like to have their pet theories or prominance in this part 
    of the internet firmament challenged, who use hyperbolic language 
    inappropriate to teh argument, who bring-in issues with nothing to do with 
    the subject, or redundant observations on the scientific matter in hand.  Of 
    which you are the worst.  
    It seems I should perhaps have stuck to my original idea, as I have no 
    interest in feeding people's egos. What I am only interested in is 
    information and exchange of ideas about navigation on a strictly factual 
    basis. Personalities and personal opinon (like this) is of no interest to me, 
    though I shall make an exception this time as you have refered to me 
    personally. It shall be my last comment of this nature.
    I have seen the same problem in political newsgroups where one or two dominate 
    with their ideas, fiercly object to any criticism, and think they are the 
    final word on high from God.  I don't buy it.  Never have; never will.  As 
    far as I am concerned there is room for objective disagreement; and if it 
    comes to an impasse then you can retain your ideas (it is your right)..... 
    and kindly allow me to retain mine and remain in my ignorance. Thank you. We 
    then leave it there until 'new evidence' arrives.
    It seems my re-engagement which was only made to add to comments directed 
    specifically to me has produced exactly what I was trying to avoid.
    For example:-
    When you describe an authoritative report from a respected journal, made with 
    the specific intent to try to bring objectivity and a scientific 
    basis/analysis to subjective measurements (as sextant observations are) in 
    terms such as:  "He describes his MISERABLE (my emphasis) results which he 
    clearly cannot explain....."
    Then I get the strong idea little feet are being trampled upon.
    I note you are an afficionado of 'Lunars' and you have on more than one 
    occasion I note, made a very strong reaction to any challenge to their 
    validity in navigation. Fine, this is Ok for you. Not to me. 
    I can cite a number of references made from various sources, contemporaneous 
    and modern, to how useless they are in practical navigation terms. One or two 
    here already have on here I note, but you dismiss all challenges to this with 
    a brush of the hand.
    As far as I am concerned, my understanding is they were promoted, developed 
    and made into a _just_ practical method by the astronomers because there was 
    nothing else possible - until the chronometer - that is all.  They remain an 
    astronomical and navigational curiosity.  It took a genius English carpenter 
    to remove them from their undeserved place of astronomical and maritime 
    prominence.  Some astronomers have never got over it I guess.
    My opinion is Lunars are inherently flawed because of the very thing which has 
    been discussed here under star distances - practical measurement to 
    sufficient accuracy  under 'normal' conditions of bouncing around in the 
    That is ignoring the difficult calculations - which they _are_ to most people 
    excepting scientists like yourself.
    I accept in modern times the calculations which were formidable to 
    pre-calculator sailors can be done more easily, but the fact remains they are 
    impractical for sailors at sea - even now.
    They were never really accurate enough to make practical use a full reality, 
    and the fact the chronometer spelt their death knell almost as soon as they 
    were invented was because of the convenience, practical use and consistent 
    results more accurate than 'lunars'. 
    If 'Lunars' were an easy, practical and sufficiently accurate method - it 
    would have carried on into the twentieth century as saiors are notoriously 
    slow to change methods. It did not. It was ditched immediately the cost of a 
    chronometer could be bourne by the shipping companies.
    I am sorry if this is anathema to you but it is my opinion and you shall have 
    to accept it, and it is unlikely to change until and unless you have hard 
    evidence to show it is not so - such as going out onto a small boat in force 
    3 using your sextant about fifty times doing 'Lunars' then with an analysis 
    of the results .... as Gordon did with the 1964 report I sent in.
    Then I might take more interest in your hearsay statements about accuracy of lunars and star distances.
    Finally; I note you have completely ignored the main aspect of my submissions 
    about star distances and sextant observational accuracy - namely the 
    resolving power of the eye itself.  
    It is well-known and demonstrable that the resolving power of the eye is 
    around half a minute of arc subtense at the eye, which is,  curiously, very 
    close to the ultimate practical accuracy of a single observation with a 
    sextant. This I have noted with practical observations I have made myself, in 
    discussion about  accuracy to friends who use sextants, (including one master 
    mariner who used them 'for real') and is confirmed in the 1964 report by 
    Gordon's report contains a very important observation - that the overall 
    accuracy of sights under various conditions was only significantly increased 
    with a telescope of greater magnification than six.  This, it seems to me, is 
    an indication of the deciding factor in this argument: you cannot increase 
    accuracy unless yuou present to the eye a much better available resolving 
    power with a telescope of good quality optics.   This is of serious practical 
    interest even today.
    I maintain that eye resolving power is the main stumbling block to any attempt 
    at increasing acuracy in sextant use, and is the limiting factor in practical 
    You have not even mentioned it.
    Douglas Denny.
    Chichester. England.
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