# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Advancing position circles: Huxtable vs. Zevering
From: George Huxtable
Date: 2006 Sep 22, 05:46 -0500

I have to report a boob I made in a recent message, when I set a
problem for NavList members. Geoffrey Kolbe has been struggling with
it, and has communicated backstage to tell me about it. Perhaps others
have been strugging in the same way.

What I did was to miswrite what should have been GHA of a star, as
Journal of Navigation. Luckily, in that Journal, I had got it right.

So here it is; right, I hope, this time.
|
| It strikes me that perhaps NavList members might like to tackle the
| simple test-problem that I set, as follows-
|
| 1. An observer, at position P1, measures the altitude of a star S1,
at
| (Dec1 = 0, GHA1 = 0), to be 30 degrees.
|
| 2. Then he travels due North by 60 nautical miles (= 1 degree), to
P2.
|
| 3.. From there, he observes another star S2 (then at Dec2 = N 1
| degree, GHA2 = W 45 degrees) to be at an altitude of 45 degrees.
Where
| on Earth is he then?
|
| and concluded-
|
| "I challenge Zevering to apply his procedure to the problem as set
out
| above, to provide us with initial and final positions for the
| observer, the initial altitude of star S1, and the final altitude of
| star S2."

Geoffrey also queries why I should be asking for the star altitudes,
when they were a precondition of the problem. That was simply to
ensure that after the positions  P1 and P2 are deduced, a back-check
is made to ensure that the result is correct. The erroneous method,
that had been proposed and I was countering, would fail such a check.

Sorry about all that. I do seem to be getting error-prone in my old
age.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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