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    Re: Index Error - Comparison to SD per Nautical Almanac
    From: Frank Reed
    Date: 2020 Nov 25, 22:09 -0800

    Lars Bergman, you wrote:

    "If my analysis is correct (I am not quite sure yet) a moon-sun lunar would be twice that amount, i.e. 0.4' too large. It is even worse with a moon-star lunar, it will be 0.8' off."

    No. It's no problem for any observations with angles greater than a few degrees, which covers all lunars except some exotic short-angle cases, which were never recommended historically, but may be of interest for modern observers, especially because they are visually "pretty" cases.

    Side error is no error. One should never fuss over it, despite the frantic worries about side offset in some textbooks. Even this apparent error in the measurement of SD is not really an error since we can predict just how large it would be based on a direct observation of the side offset in the first place, and since, in addition, we're not trying to measure that! The SD value that comes out of this observation is only for confirmation of repeatability. 

    By the way, for Jim Rives, I don't expect people to remember more than 50% of what I cover in my lunars workshops or any other of my celestial navigation workshops since they are, after all, elective activities, primarily for recreational education (and I mean that in the best sense of both words), and because I fill them to overflowing as much as I can! But yes, I do cover this business of side offset, and why it is not a source of error in all of my workshops, and I mention the possible slight difference (entirely harmless) in the SD value that results from a side offset. The fact that you remember at least part of this in the category of "common knowledge" tells me I'm doing it right. :) 

    Frank Reed

       
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