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    Re: suggestion for a satisfactory celnav narrative
    From: Fred Hebard
    Date: 2005 Jun 3, 13:10 -0400

    An appendix of things that a naive navigator might suppose are good,
    but really are not, would be helpful.  I wouldn't put this in the main
    section, except maybe to say that noon sun shots are lousy for
    longitude and to refer to the appendix.
    A fix gives both longitude and latitude without knowing either first,
    where the fix is the intersection of two or more lines of position.  A
    pure latitude shot, such as a noon sun shot, also gives a line of
    position, one that runs smack dab east-west, giving no longitude info.
    Likewise, a line of position from a body with a due east or west
    azimuth gives only longitude and no latitude.  You have to know GMT to
    use any shot other than a meridian passage shot, an example of which is
    a noon sun shot.
    You learn GMT from a watch, the radio, lunars, occultations, Jovian
    moons, etc.
    On Jun 3, 2005, at 12:26 PM, Noyce, Bill wrote:
    > Perhaps the fact that "longitude by noon sun" comes up so often
    > is a good reason that there *should* be a discussion of this
    > method, pointing out why it is a bad idea...
    > Is there any other observation that gives longitude without
    > knowing latitude first?  Maybe this is part of its appeal.
    > (By the same argument, the advanced version should discuss lunar
    > altitudes for GMT, and what's wrong with them.  I think George's
    > "parts 1-4" do include such a discussion.)
    >         -- Bill
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM] On Behalf Of George
    > Huxtable
    > Sent: Friday, June 03, 2005 8:59 AM
    > Subject: Re: suggestion for a satisfactory celnav narrative
    > Andrew Corl wrote-
    >> For Courtney, I am raising my hand to help with this.  Don't know what
    > I can
    >> do but here is a list of techniques I feel should be in the manual:
    >> Dead Reckoning
    >> Latitude by Noon Sun
    >> Longitude using a shortwave radio and the noon sun
    >> Sextant operation and how to determine the elevation above the horizon
    > of
    >> the sun, moon, star, and planet
    >> Sight reduction using H.O. 249 - method I am presently learning
    >> Sight reduction doing all the math (the "apex of celestial navigation"
    >> according to Frank)
    > As a world-weary old cynic, my opinion is that any offer, saying "this
    > is
    > how I think it should be done, and I'm prepared to contribute" is worth
    > at
    > least 10 proposals of "this is how I think it should be done, but by
    > someone else, not by me". So Andrew's suggestions are indeed useful.
    > No doubt, he expected a bit of nitpicking about his choice of topics,
    > and I
    > am happy to provide it. It relates to his suggested topic-
    > "Longitude using a shortwave radio and the noon sun"
    > Although proposals for timing the moment of noon, by observing the Sun
    > around noon, reappear on this list at regrettably regular intervals,
    > the
    > fact remains that noon is the worst possible moment for doing that job.
    > Although it's possible to make a crude assessment of the moment-of-noon
    > by
    > making an extended set of observations, before noon and after, the only
    > way
    > to get a PRECISE value of time-by-the-Sun (and hence longitude) is to
    > do
    > so
    > at a time WELL AWAY from noon, so that the Sun is rising and falling at
    > a
    > measurable rate. If Andrew were to rephrase his suggestion to read
    > instead-
    > "Longitude using a shortwave radio and a time-sight of the Sun",
    > then I, for one, would be happy.
    > George.
    > ================================================================
    > contact George Huxtable by email at george---.u-net.com, by phone
    > at
    > 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    > Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > ================================================================

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