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From: Noyce, Bill (no email)
Date: Fri Jun 03 2005 - 12:26:51 EDT
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:] On Behalf Of George
Huxtable
Sent: Friday, June 03, 2005 8:59 AM
To:
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 , 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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