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Hello
My  2 cents worth...
High altitude sights are VERY difficult to take unless your arms are strong
and steady as a rock...and indeed one plots it as a  circle of position.
himself

-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf
Of Greg R.
Sent: June 3, 2008 8:53 AM
To: NavList@fer3.com
Subject: [NavList 5257] Re: longitude around noon (a twist)


--- frankreed@HistoricalAtlas.net wrote:

> That's a good point about sights very close to the zenith. I had
> mentioned previously on the list that there may be a special case when
> the Sun is close to the zenith. I still haven't thought through
> whether it really screws up the graphical technique or merely requires
> more stringent rules for its application.

Something sticks in my mind from way back when I was first learning celnav
that for objects near the observer's zenith (i.e. Hc ~89 degrees or greater)
the resulting LOP should be plotted as a circle of position (do we call that
a COP?) around the object's GP vs. a straight line as we normally do. But I
don't have any personal experience doing that, so I can't vouch for the
technique or its accuracy.

--
GregR




> I made one last try at convincing George Kaplan (a name some of you
> know) to
> join us in Mystic this week, but alas, it's not in the cards.
>
> While I was at it, I chatted in my email a bit about longitude around
> noon and asked him this:
>  "Which leads to a question: is there an established name in the
> literature, or even in your own jargon, for a fix resulting from a
> series of ten or twelve sights taken over a relatively short period of
> time? I've been
>
> calling it a "rapid-fire fix". Do you know another name?"
>
> His reply:
>  "I don't know of a special name.  You're correct, of course, if you
> can get a bunch of sights on either side of noon, you can get good
> enough geometry to get a 2-D position.  It works with the LOPs, too,
> in that they provide a good spread of azimuth around then.  There is a
> slight catch, however, and that is, the higher the Sun is in the sky
> (and therefore the more rapid the altitude and azimuth change near
> noon) the more you have to worry about the curvature of the LOPs.  In
> some near-degenerate cases (sun within several degrees of the zenith),
> the usual straight-line plotting -- or math that assumes straight-line
> LOPs -- may not provide the right fix."
>
> That's a good point about sights very close to the zenith. I had
> mentioned previously on the list that there may be a special case when
> the Sun is close to the zenith. I still haven't thought through
> whether it really screws up the graphical technique or merely requires
> more stringent rules for its application.
>
>  -FER
>
>
>
> >
>






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