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--- "Greg R."  wrote:

> 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)

That should obviously be Ho vs. Hc - that'll teach me to post before
I'm fully awake...  ;-)

--
GregR



> --- 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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