Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Fix by equal altitude sights around local apparent noon
    From: George Huxtable
    Date: 2009 Oct 13, 11:31 -0700

    Frank Reed, in message [10104], responded to a rather-odd posting [10103], 
    from within the archive, from (presumably) geo589{at}exemail.com.au , 
    replying to an earlier posting by a chap called Malcolm Misuraca, which was 
    full of sound and fury.
    
    That earlier posting, and that name, seemed completely unfamiliar, until Frank 
    explained all by dredging down into the archive, and quoted a post, back from 
    November 1997! That was well before Frank's time on this list or its earlier 
    equivalent, and indeed, a year or two before I got involved. Dan Allen has 
    participated throughout, and his name cropped up in those days too; Paul 
    Hirose as well. Indeed it's thanks to Dan that the archive from those days 
    has been preserved at all, though it appears to be somewhat incomplete from 
    those early years.
    
    Frank added- "Also, in case anyone new is curious, "Nml" was the original name 
    for this discussion group (before "Navigation-L" which was before 
    "NavList")."
    
    However, I doubt whether that's the case. I see that "Nml" tag in archived 
    postings from my own early days on the list, when it's name was certainly 
    "Nav-l" and I remember no "Nml". I suspect that the tag "Nml" may relate more 
    to where the list's doings have been archived, rather than to the name of the 
    list itself. Dan should know.
    
    Indeed, the Navlist archive seems to have chosen to subsume all of the Nav-l 
    archives within itself. Nothing wrong with that, it's a sensible thing to do, 
    but is there a way to tell which forum a particular posting went to? If not, 
    there should be. Remember, for a (short) time, both lists existed in 
    parallel, without cross-correspondence.
    
    =============================
    
    Enough about our archive, and now back to the subject of that old Misuraca 
    posting, which I won't quote again, as Frank has done so in [10104], with 
    this comment - "Note that this message by Mal Misuraca was clearly part of 
    some more involved discussion, however we do not seem to have any of the 
    other original messages from this one."
    
    But we do. There were a few messages in the previous month October 1997, on 
    that topic. Some were inconsequential or illogical, but the one that appears 
    to have triggered Misuraca's outburst was on October 28, 1997, from Tony. I 
    suspect that this was perhaps Tony Severdia, from San Francisco, a regular 
    correspondent from those days, no longer with us. He and I used to enjoy 
    occasionally crossing our pens, and, on other occasions, agreeing.
    
    It's worth reading what he had to say, which brought about such a reaction from Misuraca.
    
    Under the subject heading "fix with the noon shot", Tony wrote-
    
    ==============
    
    "PULEEZE ...folks!
    
    This same proposition (in many cases nicely thought out _in theory_) is 
    proferred about every three months on this very list.
    
    I offer for your learned consideration:
    
    1. If a true "fix" were possible, it would be heralded in any and every 
    navigation text you might have ever read.
    
    1a. A fix by definition is the most accurate position that can be attained by 
    the navigator by (in this case) celestial means.
    
    1b. The sloppy navigator can, of course, obtain a _rough_ _estimate_ of 
    longitudinal position by making many compromises. If he has not the slightest 
    idea of his longitude, it is better than nothing (Chuck was on the mark here 
    with lifeboat nav).
    
    2. While theoretically possible, EVERYTHING near LAN dependson _absolute_ 
    accuracy of the sextant altitude sight, time and related factors.  (delta 
    declination, North/South, East/West sailing tracks are _only_ a very _minor_ 
    part of the equation).
    
    The best method is to bow to well proved practices of well time-spaced running 
    fix ...then one can call it an "Rfix". (But, still certainly not as good as a 
    true celestial fix).
    
    Sorry to be so didactic, but the proposition keeps coming up as earlier 
    mentioned ...with some folks proferring "a new revalation".
    
    Everything depends on what measure of innacuracy _you_ are willing to accept.  
    SURELY, NO ONE would accept such rough approximations in approaching atolls 
    or landfall!
    
     A Navigator's well kept DR since last true fix is very probably much better.
    
    Wasted words?  I hope not!  Bye.
    
    Tony    San Francisco, CA
    (Home of NAVIG94)
    
    =====================
    
    Tony's opening words in 1997, "This same proposition (in many cases nicely 
    thought out _in theory_) is proferred about every three months on this very 
    list." have proved only too true, ever since.
    
    In spite of the recent support proffered by geo589{at}exemail.com.au , 
    Misuraca's old posting comes across to me as long on polemics and rhetoric, 
    but lacking in clarity of logic, as Jim Wilson has pointed out. I suspect, 
    from a look into Google, that Misuraca is an American lawyer, which may 
    explain something. And his subtitle, "Celestial in a day", may explain rather 
    more. If his aim was to teach celestial IN A DAY, no wonder he went for 
    short-cuts!
    
    As a result, a generation of "navigators" may be going home, to say, "Ma, 
    today we learned celestial navigation", and think themselves competent to 
    sail around the World. But, it appears, with no concept of a position line, 
    no familiarity with observing anything other than the Sun, and that only 
    around noon, if it happens to show then for a sufficient interval. No concept 
    of what a sine is, or a cosine, even though all the drudgery is now removed 
    from using such things by the availability of calculators. And with only one 
    method of determining longitude, a way that calls for exquisite precision of 
    observation, repeated, to achieve a mediocre result. And throws away all the 
    precision that a navigator's craft is able to deliver, when it's been taught, 
    and learned, and applied properly.
    
    The only thing that can be said in favour of such lazy teaching is that it's 
    intellectually undemanding, because it involves no trig. If the aim is to 
    give the appearance of learning, without the substance, then that fits in 
    with the modern demand for instant gratification. Fair enough, if there's no 
    pretence that this is real celestial navigation. I pity the serious student 
    who has signed up for such a course, hoping to understand the real thing, and 
    finds himself short-changed.
    
    But there's little fun in arguing against such a view in the absence of its 
    proponent, who has long since quitted our scene. However, this same argument 
    is doomed to run and run, just as Tony predicted. Frank Reed has his own 
    views, which differ greatly from my own, and listmembers are by now painfully 
    familiar with both.
    
    =========================
    
    Mal Misuraca, 12 years ago, offered to copy pages from volume 3 of the 
    Admiralty Manual of Navigation, 1958, on the topic, and 
    geo589{at}exemail.com.au , thinking that to have been a recent posting, 
    requested just that. I can't offer that edition, but I can supply a copy of 
    the 1938 edition, where the moment of LAN is treated in great detail. That's 
    mainly from the viewpoint of predicting the correct moment to observe for 
    meridian altitude; for latitude, not longitude. It includes a table to ease 
    calculation of the time interval between meridian passage and maximum 
    altitude. However, it offers a section, starting on page 156, which I copy 
    here. To preserve precision of such an equal-altitude observation, it sets 
    very restrictive conditions on the separation of azimuth from due-South, and 
    on altitude and declination of the Sun, which are far removed from the notion 
    of longitude-around-noon that proponents of the method take for granted. 
    Under those restrictions, the method can indeed be very precise, but it 
    becomes longitude-nowhere-near-noon.
    
    If anyone has a copy of the 1958 edition, it would be interesting to learn if it says any different.
    
    George.
    
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    www.fer3.com/arc 
    
    
    
    File:


    --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To unsubscribe, email NavList+unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    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