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Jeremy, you wrote:
"So we need to get at least 2 Sumner points, and preferably three to expose 
plotting and/or math errors. Sounds like at least as much work, if not more, 
than St. Hilaire.  I don't know, since I've never plotted Sumner lines.  As 
an aside, we use the same equations with different names in our Great Circle 
sailings."

Yes. That's the big thing: calculational cost. 

Your comment about great circle sailing is true, of course, and it reminds me 
of a brief era, so long ago, when I had access to a software tool that would 
calculate great circle distances (from a terminal on a main-frame computer). 
That's what it was designed to do, and it requested its inputs for that 
problem. I used it to solve other spherical trig problems when necessary, and 
in those days I could actually still impress people by saying "when it asks 
for the 'latitude of the first city', just enter the declination of the 
star." Ha! Times change.

You also wrote:
"Why is Blu-Ray better than HD-DVD, or VHS better than Betamax?  It was 
adopted over time and tradition truly does rule the seas."

The supremacy of tradition in celestial navigation is very real (and I'm not 
saying it's a bad thing), but it sometimes creates the impression of 
perfection where it shouldn't. The inertia of navigational tradition does 
indeed share some aspects of consumer inertia (like the examples you've 
given), and this fact is not generally recognized by navigators. Modern, late 
20th century celestial navigation reached a plateau of efficiency just about 
the time it was being replaced. From about 1960 to 1990, celestial navigation 
was largely a fixed, unchanging set of procedures. In some ways, this is 
comforting for users and enthusiasts, too, but it's a mistake that some 
people make (not you) to think that earlier methods of navigation were "not 
really proper" celestial navigation, and it's a mistake that some other 
people make (not you, not anyone specific here) to think that there can be no 
modern variations that would be more useful under some circumstances, more 
teachable under other circumstances, or even more accurate under still other 
circumstances.

-FER



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