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Re: Position from altitude and azimuth.
From: Bill Lionheart
Date: 2020 May 20, 07:18 +0100
From: Bill Lionheart
Date: 2020 May 20, 07:18 +0100
Just to be clear I concluded that an isoazimuthal curve is not a small circle although it can be close. It has a variable curvature and non zero torsion.
Moreover the angle subtended by a chord at the circumference of a circle on a sphere is not constant.
Bill
On Wed, 20 May 2020, 02:32 David Pike, <NoReply_DavidPike@fer3.com> wrote:
Bill Lionheart you wrote: So the discussion Frank and I were having off list is how how to turn this in to a proof that the isoazimuth is a small circle.
I’ve been thinking about this and I’ve come to the conclusion that it’s important here to decide whether we mean ISO Z and ISO Azimuth. E.g. consider Dec 30N and azimuth 060. Z can flip at GHA + 180 , such that Z is still 60, but azimuth is now 360 – 60, so you’ll get a ring which might or might not be a perfect circle. If you stick with ISO Azimuth. Your saying the direction of the star is always at 60 degrees to the meridian, so in this particular case you’d get a spiral. DaveP
