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    Re: Lunar Distance in Wikipedia
    From: Paul Hirose
    Date: 2007 Jul 27, 13:48 -0700

    George Huxtable wrote:
    > Trouble, is, the various sections on that page all interrelate, so it's hard
    > to tinker with one without altering others. Nor do I think the way the topic
    > is divided under different headings is entirely sensible.
    I think the article has too many headings. One for each paragraph is
    excessive. The main part of the article (if you omit the Theory
    paragraph) actually reads more smoothly if you pretend the headings
    aren't there.
    > I wonder if there are specific rules about the length of such
    > contributions.
    There is a Wikipedia style guide, and even an article about article size:
    The amount of stylistic guidance is somewhat intimidating. It's a good
    thing you can't get fired for breaking a rule.
    > "In celestial navigation, lunar distance is the angle between the Moon's
    > centre and the Sun or a bright star, slanting across the sky, as measured
    > using a sextant. Such an observation, usually abbreviated to just "a lunar",
    > can be made by a mariner, anywhere in the World, if the Moon is visible,
    > together with the Sun or a special star. Without needing a chronometer, it
    > allowed him to calculate what the time was at some reference longitude
    > (usually Greenwich) at the moment of that observation, using data which used
    > to be published in a nautical almanac. That was an important step in finding
    > his own longitude, from Greenwich."
    All of that is correct as far as I can tell. However, I believe less
    detail and precision are appropriate for a lead paragraph. E.g., "In
    celestial navigation, lunar distance is the angle, observed with a
    sextant, between the Moon and the Sun or a star." (Were planets used too?)
    It should be obvious that both bodies must be visible, so to continue,
    I'd just say, "From such an observation, usually called 'a lunar', a
    navigator can obtain Greenwich time. That enables the determination of
    longitude without a chronometer."
    > In Celestial navigation, precise knowledge of the time at a reference point
    > and the positions of several celestial objects are combined with careful
    > observations to calculate latitude and longitude. But reliable marine
    > chronometers were not invented until 1761, and were not generally available
    > for many decades afterwards. For nearly one hundred years (from about 1767
    > until 1850), the method of lunar distances was used to determine Greenwich
    > time, in order to deduce the longitude at the time of the lunar observation.
    > Such time information could also be used to check chronometer error.
    In the first sentence, rather than "a reference point", I would use
    "Greenwich". While the former term is more strictly correct, it's also
    more abstract. I think most readers will be best served by simply using
    Greenwich as the basis for the almanac, time, and longitude.
    The paragraph puts the era of lunars *after* the invention of the
    chronometer. I don't question the historical accuracy, but it reads
    oddly. Perhaps the second sentence could simply say, "But accurate
    Greenwich time from chronometers was not generally available at sea
    until well into the 19th century." I believe that would make a smoother
    transition between the first and third sentences.
    > "This method relies on the relatively quick movement of the Moon across the
    > background of the stars. Although the Moon, with every other body, appears
    > to circle round the sky in about 1 day, with respect to the star background
    > it completes a circuit in 27.3 days, and with respect to the Sun in 29.5
    > days. This implies that with respect to the Sun and to stars that lie near
    > its path in the sky, it is moving by approximately its own diameter, about
    > half a degree, every hour. So lunar distances to those bodies are generally
    > changing at about that rate, some increasing, others decreasing. That motion
    > of the Moon is by far the fastest such change that can be seen in the sky,
    > and because it is predictable in advance, it can be used as a measure of
    > time. Wherever on Earth the Moon is seen from, at that moment, observers
    > will agree about that time. If the predictions they use are based on
    > Greenwich, that time will be Greenwich Time.
    That's better, though I believe the apparent daily rotation of the
    heavens is familiar enough to the general reader that it need not be
    mentioned. So for the second sentence I'd say, "It completes a circuit
    of 360 degrees in about 30 days, equivalent to 12 degrees per day. This
    implies..." This combines less mathematical precision with a bit more
    filling-in on how the figure for angular rate is derived.
    Is this a good place to mention the almanac? Perhaps the last two
    sentences could be replaced with something like, "If lunar distances to
    selected stars are tabulated at intervals of Greenwich time in an
    > As for the bit that caused the trouble to start with; the section headed
    > "Theory", I think it's awful, in so many ways, that just tinkering with it
    > will not do. For example, why invoke two observers, when in reality there's
    > only one? It needs a complete rewrite, and I will think about that.
    Amen. Maybe delete the current Theory paragraph and use the one under
    the Method heading instead.
    A "obituary" paragraph at the end would give a nice sense of
    completeness to the article. E.g., "Lunars went out of fashion when..."
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