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Lu Abel wrote:
 > Sights are reduced (with a calculator, at least) by solving a 
spherical triangle with the vertices being the observer's DR position, 
the body's Geographic Position, and the "elevated pole," the pole, North 
or South, closest to the observers position.

To be more precise, the elevated pole is the one closest to the 
observer's *assumed* position. It need not be the one closest to the 
true position. That's a good thing, because very near the equator you 
may not be sure which side you're on. But if you guess north when you 
are really south, there's no harm except that the intercept is longer 
than necessary. The math still works.

For example, LHA = 315, assumed lat = 1N, dec = +45. HO 229 says Z = 
35.6. If assumed lat = 1S, Z = 145.1.

Applying the rules for azimuth, Zn = Z = 35.6 in the first case. In the 
second case, Zn = 180 - Z = 34.9. A smaller azimuth is reasonable in the 
second case, given the different assumed position.


Gary LaPook wrote:
> Interesting, you're right, you don't actually need to make that last math 
error, er, conversion to Zn in order to plot the LOP. Well, you do, at least 
in your head, because the roses on charts and plotting sheets do not have the 
proper scales for Z. Now if somebody made an aircraft plotter with a second 
scale running counter clockwise (actually, clockwise because the scale on an 
aircraft plotter already runs counter clockwise because how it is used) then 
it would be simple to just use Z.

No special scale is needed, Gary. Ignore the numbers and count degrees 
in the appropriate direction. For example, suppose the south pole is 
elevated, the body is west of the meridian, and Z = 33°. I.e., the body 
bears roughly SW by S. Set the plotter at right angles to a meridian. 
That's the orientation of a celestial LOP if Z = 0. Then rotate the 
plotter clockwise: "There's 10, 20, 30... 33." The numbers are merely a 
visual aid to help your eye count tens. It doesn't matter what they say.

This is easier to do than explain. Once the trick is learned, you can 
forget the azimuth rules.

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