NavList:

While the exact altitude can be readily computed by a variety of means, it is a different thing altogether when actually shooting the body.  The best you can do is stand over a compass and point the sextant in the correct direction (Assuming of course that you are actually shooting the body at the time that you pre calculated the azimuth for which can certainly not always be possible),

 

"Rocking" the arc and twisting the body to find the nadir is far more difficult with high altitude stars which was my point.  You can easily record the incorrect altitude by being off a few degrees in azimuth.  The loss of LOP quality happens in the observation process, not in the reduction process.

 

Jeremy

 

 

I agree Jeremy did a fine job discussing the art of LOPs (http://fer3.com/arc/m2.aspx?i=114851).

Just one minor point of disagreement, where he says: " Very high altitude stars make it difficult to determine the exact azimuth and can lead to false observations."

The azimuth used in St. Hilaire is computed and is therefore without error (i.e., can be accurate as we like). Using this computed azimuth from the AP and the intercept gives a point on the LOP (a PLOP) which can only be in error due to the altitude measurement.

John
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