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    Re: AP terminology, WAS: 2-Body Fix -- take three
    From: Gary LaPook
    Date: 2009 Nov 13, 17:06 -0800

    I programed my TI-59 calculator a long time ago to compute Sumner
    lines. I input the DR, date & time, altitude and name of the body. The
    program then computed the latitudes where the LOP crossed the
    meridians immediately east and west of the DR. If the orientation of
    the LOP was more north-south the program computed the crossings of the
    parallels north and south of the DR. It was really easy to plot since
    the charts would usually have the minutes of latitude and longitude
    already printed so I only had to lay a straight edge across the points
    and draw in the LOP.
    
    With calculators the doubling of effort to do the two computations is
    trivial but it wasn't so in the olden days, hence the popularity of
    St. Hilaire.
    
    gl
    
    On Nov 13, 2:49�pm,  wrote:
    > 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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