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--- 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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