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Subject: Re: It Works.
From: Arthur Pearson (arthurpearson@XXX.XXX)
Date: Mon Apr 08 2002 - 17:41:25 EDT
Bruce et. al.
Our digression into SHA meridian was not time wasted; I have finally
grasped the concept. Although we may conclude that given Bill Noyce's
insight, the method is unnecessary, I think it is remarkably elegant
solution. As I now understand it, LAN is essentially used as a way to
mark our place on the SHA scale without regard to exact time or
longitude. The SHA Sun simply does not vary much over an hour (about
3.4' in the hour I looked at), so this is pretty accurate even without
exact time. Convert to arc the time from LAN to the lunar to we can get
SHA meridian at the time of observation within +- 3' roughly. That's
pretty good for a vessel with a chronometer that may be out by 30
minutes or more. It is as if one re-set the "SHA Clock" each day using
LAN. A very elegant derivation, I can't help but think there are other
uses for the principle.
That said, I am relieved by Bill's insight that if we are using
celestial fixes to begin with, the error in time and longitude will
cancel out. It eliminates the need for special procedures in
anticipation of a lunar. I need to work out the example to make sure I
understand it, but it does feel we have come full circle.
Regards,
Arthur
-----Original Message-----
From: Navigation Mailing List
[mailto:NAVIGATION-L@XXX.XXX] On Behalf Of Bruce Stark
Sent: Monday, April 08, 2002 2:42 PM
To: NAVIGATION-L@XXX.XXX
Subject: Re: It Works.
Like George, I've been "Off watch." But for longer time and for less
interesting reasons, one of them being that a backhoe took out our
telephone
line.
A lot of good postings. William Noyce's insight, that the problem we
were
discussing on the "It Works" thread takes care of itself, is beautiful.
Why
didn't we see that?!
I'm sorry now I posted that method of finding SHA meridian, etc. It
injects
the old nautical astronomer's way of thinking into the discussion. It
isn't
needed, and confuses the issue. Arthur and others should forget about
SHA
meridian and put to practice what William has said. That way they will
see
how it works and develop confidence.
Don't think I have anything to add to what George has said. Glad he
pointed
out that noon is the worst time to get local time.
Hope the "Artificial Horizon" thread will remain as lively.
Bruce
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