# NavList:

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

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Re: angles betwqeen lines of position
Date: 2012 Jul 17, 21:28 -0700

Hi Alan

As Bill has correctly pointed out, you are confusing two angular identities.

When you are plotting LOPs, the azimuth of the observation dictates the angle of the line on the chart.

The rotation of the earth yields that 15 degree per hour rate.

Consider the situation if you ate standing on the equator, with the sun's declination to be zero.  Every hour, the elevation of the sun will change by 15 degrees.  Yet the azimuth before meridian passage remains constant east, and after meridian passage constant west.  In this ideally constructed experiment the angle will flip 180 degrees nearly instantaneously, with the azimuth ill defined when coincident with your zenith.

So now you must see that the angle between LOPs will not track the 15 Degree per hour rate.  Of course, you can get it to occur.  For example, very near to the pole shooting at a fixed star.  Precisely at the pole, azimuth is ill defined, yet near the pole, it retains meaning.  So your azimuth to the star will match the rate of earth's rotation (for all practical purposes).  I'm sure that there are others.

Shooting with an artificial horizon has no bearing upon the problem.

As usual, should I have blown any of the explanation, I will be corrected forthwith by the cognoscenti of the list.

Kind Regards

On Jul 17, 2012 11:53 PM, "Alan S" <alan202@verizon.net> wrote:

Bill B:

Possibly I should have mentioned it, I was shooting using a Davis Artificial Horizon. Does that effect the thing?

Alan
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