NavList:

Bill you wrote:

"This is where I get lost in the jargon. Does "calculate geodesics on the
Earth as shortest distance arcs on the ellipsoid" mean that corrections for
the fact the Earth is not a perfect sphere are included?"

 

Yes. A geodesic, by the definitions of geometry, is the path with shortest distance between any two points (technically "extremal" length). On a spherical Earth, the geodesics are great circle arcs. Because the Earth is ellipsoidal, there is an advantage in distance gained by staying away from the equator (where the Earth is fat). This means that the geodesics are slightly curved. If you are directly above the middle of a great circle arc, it will appear exactly straight to you, unlike the geodesics on the ellipsoid.

 

And:

" Is this "GCD?" This would be more accurate than calculations that assume the Earth is a
sphere, correct?"

 

I think HP was using GCD just to save the time of typing out "Great Circle Distance". Calculating the distance based on ellipsoidal geodesics is "more accurate", yes, but not in any practically useful way that I can think of. Anybody know of a practical use?

And:

"I also have not resolved the question posted earlier: "My confusion is that
132d is the starting course of a great-circle  route. I am having trouble
understanding why that would be my azimuth. (spherical trig is still a
plug-and-chug function for me)."

 

Try drawing the two spherical triangles involved - one for the calculation of the great circle distance between two places on the Earth (assumed spherical for this), the other for the calculation of star's altitude. Does this help?