Next message: Bill: "Re: Anomalous dip. was: [NAV-L] Testing pocket sextant."
George wrote, a few days ago:
"Consider this simple example, once again.
3 observers, A, B, and C, see a star positioned at dec = 0 degrees, GHA
= 0 degrees, at an altitude of 30 degrees. A is at 60N, 0W, B is at 0N,
60W, C is at 45N, 45W. It is obvious that A and B are on that circle,
centred at 0N 0W, radius 60 degrees, and a bit of simple spherical trig
(or altitude tables) shows that C is also exactly on the circle. Each
observer travels due North through a distance of 60 miles. Now A is at
61N, 0W, B is at 1N, 60W, C is at 46N, 45W. Do those 3 new positions lie
on a circle? If so, where is its centre and what is its radius? I
guarantee that nobody will provide such a centre or radius, because
those positions are no longer on a circle. And the discrepancy from a
circle is not by an infinitesimal amount, either.
but by something over 14 miles, after a shift of only 60 miles."
Being well aware that Alex has pointed out that 3 points will be parts
of a circle, it is interesting to calculate the centre and radius in
George's example:
centre 0.378380N 0.625482E
radius 60.623519 degs
/Lars
