Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Lat/Lon by "Noon Sun"
    From: Geoffrey Kolbe
    Date: 2009 Apr 14, 08:14 +0100

    NavList 7929 George wrote:
    >My heart sank, somewhat, on reading Frank Reed's resending of a
    >four-year-old post, on a familiar topic.
    Well, to balance the boat somewhat, I would like to say thanks to Frank for
    (re)sending a nicely written piece describing the details of a very basic
    celestial navigation method. I think some of George's criticisms are unfair
    and show that he has not read Frank's piece properly. Frank is more than
    capable of responding to George, but my response may be viewed as more
    impartial and so the more credible for that. So, here it is.
    >But from his words, "You can cross oceans safely and reliably for years on
    >end using this technique if it suits you to do so", Frank Reed appears to be
    >advocating it as The Way to teach Celestial Navigation to students, and it's
    >this that I regard as dangerous.
    This, for example, is not what Frank said. What he actually said was,
    "...The days are gone when celestial navigation was essential and fixed
    curricula could be dictated for students to either take in their entirety
    or leave. This field has moved on to the stage of "a la carte" learning. It
    can be a pain in the neck for instructors accustomed to doing things the
    same way year after year but it's a real liberation for students..." So,
    far from advocating "The Way to teach Celestial Navigation to students",
    Frank is saying just the opposite - there is no set way to teach celestial
    >I have not yet met a graduate of the Frank Reed school of Celestial
    You have met me George and this method is how I started out getting to
    grips with celestial navigation. Having graduated from the "Frank Reed
    school" and my interest aroused, I then went on to gain "a rounded
    understanding of position lines and sight reduction, how to read a nautical
    almanac, how to use the Moon or take a twilight round of star
    observations..." Frank's point, though, is that it was not necessary to go
    on and do the post-grad course to be able to navigate successfully and
    safely around the world - provided the limitations of the method are born
    in mind. But that is true whatever method is used.
    >But if students are led to believe they have learned Celestial Navigation,
    >from the handling of Sun noon sights alone, avoiding any trig., then a
    >generation of navigational incompetents will arise; "one-club golfers" who
    >will quickly become lost at sea, if the Sun doesn't shine for the requisite
    >hour around noon. It would be the dumbing-down of a skill, delivering
    >instant gratification without the necessary groundwork.
    Once again, Frank is not leading anyone to believe that if they have
    learned this simple method and use it exclusively, then they know all there
    is to know about CN. And why should a generation of navigational
    incompetents arise because one person chooses this particular method from
    the long menu available of CN methods and finds it to his liking?
    To say that they will "quickly become lost at sea" by being such a "one
    club golfer" is gross exaggeration George, as I am sure you know.
    "Celestial Navigation" is actually done as a check on dead reckoning. If
    the sun does not shine for a few days, it just means the uncertainty in
    your position grows. It does not result in you being "lost at sea".
    >Now for a bit of detail about that posting.
    >The claim is made that it will get you "latitude and longitude to about +/-2
    >miles and +/-5 miles respectively". Certainly, there are many situations
    >where that will indeed be the case, but Frank has been asked about more
    >difficult environments, with a low Sun at noon, at higher latitudes and
    >rough weather conditions affecting the precision of sextant sights, but has
    >not responded by conceding any worsening. If we ask what assumptions have
    >been made about the various uncertainties, in course and speed, and
    >altitude, and how they combine, in such difficult cases, such questions have
    >been evaded.
    Obviously, in polar regions, this "Noon Fix" method is going to be quite
    useless. But even if global warming means that the North Pole is going to
    be ice free in the summer months, nobody is going to go club sailing up
    there using only this method for navigation. I think that the point was
    made four years ago that in the latitudes at which, and the seasons in
    which, people usually go sailing recreationally, Frank's claimed accuracy
    was reasonable.
    And hang the corrections for refraction, dip and semi-diameter for getting
    latitude. For a small boat where your feet are at sea level, just shoot the
    centre of the sun and call it good. The resultant accuracy in latitude will
    still be better than the claimed +/-5 miles for longitude.
    >First, for comparison, lets consider what a navigator using position-lines
    >has to do, to get a precise position by the Sun. That calls for one
    >observation sometime mid-morning, and another in the afternoon, at
    >any-old-time, whenever the Sun happens to shine. He has to correct those
    >altitudes, get Sun positions from his almanac, work two sight-reductions to
    >get azimuth and intercept, draw two position lines, shift one according to
    >his DR, and plot where they cross.
    Yes George, but this requires a much higher level of understanding and
    competence than the noon fix method. As Frank pointed out, for occasional
    practitioner of CN, it is much easier to understand and - importantly - to
    re-acquaint oneself with the Noon Fix method when needed, than the position
    line method with its attendant mastery of a sight reduction system.
    >Compare that with the task that faces the man who wants to get a "fix around
    >noon". The suggested sequence requires the navigator to be taking and noting
    >timed Sun sights over a period of 40 to 60 minutes, resulting in 5 to 13
    >observations. To achieve any sort of accuracy, in most conditions the longer
    >time and the greater number will be called for, as I will assume. This must
    >be done at predefined times, irrespective of other urgent jobs arising on
    >board, such as attending to sails.
    Once again George, that is not quite what Frank said. He said it required
    some 10 minutes of your time during that 45 minutes, taking and recording
    sightings, and another 5 minutes reducing the data (which can be done any
    time). And do these observations have to be done at predefined times? I
    don't think so. Even in a busy schedule, it should not be too difficult to
    snatch a minute here and there to take sights. If your schedule is too busy
    to do that, I suggest your boat is seriously undermanned!
    >Frank tells us that the job can be done without need of a nautical almanac
    >"you don't need one at all --only a short table of declination and equation
    >of time, possibly graphed as an "analemma" perhaps (he says). He doesn't
    >tell us what precision is available in the use of such a tool, and to what
    >extent his claimed precision of 2 miles in lat, 5 miles in long, would be
    >degraded by it. I would like to know. He doesn't even mention that without a
    >full almanac, both declination and equation of time need to be interpolated
    >between given values for two Greenwich noons, according to the observer's
    Even with a "full almanac", some interpolation is required for the position
    of the sun at any given time. Frank did say that if an analemma is used for
    the equation of time, its scale should be "sufficient". I think that for a
    short monograph such as Frank wrote, it is not necessary to go into details
    on exactly what scale is required. No doubt Frank could give an answer to
    this - but the purpose of the posting was to put forward the idea that a
    noon fix method could be used successfully to find one's position and give
    some flavour of how it could be done. Within those limitations, I think
    Frank succeeded admirably.
    And, to finish George, I don't recall Frank ever saying that this Noon Fix
    method was his "favourite project". This is clearly a personal jibe of a
    rather bilious nature which is not necessary.
    Geoffrey Kolbe
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site