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    Re: Lunar Distance in Wikipedia
    From: George Huxtable
    Date: 2007 Aug 4, 10:52 +0100

    Renee has made further useful updates to that Wikipedia article, and writes-
    | George, I have taken your suggestions for "Why" and "Method" into the
    | article.
    | As you can see from the end notes, I have referred repeatedly to the 1928
    | edition of Norie, with links to the digitized version available at the
    | Mystic Seaport website.  This makes it easy for anyone reading the article
    | to check the citations.  I also cross-reference within Wikipedia quite
    | freely (again using links), but don't cite encyclopedia articles.
    In my comments about the Norie references, I hadn't realised just how
    accessible Renee's links made them. Sorry about that. I see there's now also
    a useful link which downloads some lunar distance pages from a Nautical
    Almamac (1804): just what's needed.
    Some suggestions for minor tinkerings-
    Everywhere, reference is made to Greenwich and "Greenwich Time", as being
    THE reference point for longitude. This is a thoroughly Anglocentric
    viewpoint. Should there be a mention somewhere of the use by others of other
    bases, such as Paris, for time and longitude? In fact, the very first lunar
    distances, predicted and observed, were by LaCaille, and the French in
    particular resisted the adoption of Greenwich for many years.
    Under "the reason..." is the sentence- "But accurate Greenwich time from
    chronometers was not generally available at sea until well into the 19th
    century." That could provoke argument about "not generally available". Would
    it be better to change it to the following?
    "To many mariners, chronometers, showing accurate Greenwich time, were
    unavalable or unaffordable until well into the 19th century".
    Under "Method" are the words-
    "That could be the Sun or one of a selected group of bright stars lying
    along the ecliptic". That's rather too precise to be true, as the stars are
    scattered around the ecliptic. Better I suggest, to say something like-
    "... one of a selected group of stars which lie close to the Moon's path,
    near the ecliptic", which gives a clue as to why those stars were chosen.
    Neither those stars, nor the Moon's path, are actually on the ecliptic.
    There's a reference to miles, taken from text I may have suggested, but it
    now strikes me we should have been more specific and said "nautical miles".
    Under "History", the text remains as giving "HMNAO Nautical Almanac for
    1850" as the end-point for lunars, which is certainly wrong (where did it
    come from?). I have an almanac for 1862 which includes lunars, and think the
    last year should have been 1906. I can see that Renee wished to distinguish
    between the British and American almanacs at that point, but labelling it
    HMNAO is not the best way to do that. Yes, HMNAO is indeed Her Majesty's
    Nautical Almanac Office, but I wonder whether it had that title a century
    ago? Better to say simply  "British Nautical Almanac": although other
    British Almanacs existed, everyone will understand.
    I'm not sure what Fred is asking for, but I think he wishes to include a
    discussion of the various procedures for clearing a lunar. I would resist
    that, as it would unbalance the article. I think it was Mendoza who claimed
    to identify over 100 such methods, and that was in the early 1800s! It may
    however be useful, when we get round to the corrections,  to simply say that
    many such methods have been developed, and possibly provide a reference.
    Even though it has many shortcomings, I would suggest Charles H Cotter, A
    History of Nautical Astronomy, London 1968, chapter 6.
    It was suggested that Frank's recent proposal for using lunar distances to
    find positions, essentially from the parallax, might get a mention.
    Interesting though those ideas may be, I suggest they would be out of place
    in an encyclopedia article, which should concern itself with mainstream
    principles and practice, rather than with the more exotic outliers. Do
    others agree?
    | * In the paragraphs you are throwing around, could you add
    | sources that support your assertions?
    |  "In the early days of lunars, predictions of the Moon's position were
    | only to half an arc-minute (citation needed here)..."
    That's a very fair question, Renee. I can offer these 3 clues.
    1. The British Mariner's Guide, Nevil Maskelyne, London 1763. Preface, page
    3. "...Mr Mayer's printed tables, which I have reason to think, applied to
    careful observations, will determine the longitude always with a degree, and
    generally within half a degree." That would imply that the overall error,
    prediction + observation + calculation, would be always within two minutes,
    and generally within one. From that, we have to infer what the prediction
    error alone might be.
    2. Eric G Forbes, "Tobias Mayer ..." Goettingen 1980, refers on page 204 to
    work by Charles Mason (he of the Mason-Dixon line) "... Mason succeeded in
    reducing the mean error in the Moon's celestal longitude to one half of its
    former amount, that is, to about 30 arc-seconds. Nevertheless, although his
    results were quoted to the nearest 0.1 arc-seconds, Mason still found
    differences of 19 arc-seconds or more between 66 observations of the Moon's
    longitude...". Those results were published in "Mayer's Lunar Tables,
    improved by Charles Mason" (London 1780), but I am not familiar with that
    3 . Nicholas A Doe, "Captain Vancouver's Longitudes 1792", in Journal of
    Navigation, Vol 48, No 3, Sept 95, pages 374 to 388.
    Renee wrote-
    | I am liable to make more errors the deeper I get involved in matters about
    | which I know practically nothing.
    I think Renee is doing rather well. She invites us to get involved, with
    useful tips, but I for one would prefer it if our list continues to use
    Renee, and her skills, as our conduit to Wikipedia, if she doesn't mind too
    much. In that way we could avoid re-editing each others' contributions. I'm
    sure Renee can weave a path between contradictory opinions, if that becomes
    necessary. If she gets fed-up with acting as go-between, I hope we'll be
    told so.
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    To post to this group, send email to NavList@fer3.com
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