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    Re: Precomputed lunar distances
    From: Bill B
    Date: 2005 Apr 20, 00:25 -0500

    Frank
    
    > Bill you wrote:
    > "In fact that is not what raised a red flag for me.  I had drilled  down too
    > far and done a scatter graph with Excel, so every or hundredth or  thousandth
    > was magnified."
    
    Frank responded:
    
    > Yeah, I wondered if that was part of the problem. Remember, if your input
    > data is accurate to the nearest tenth of a minute of arc, generally you should
    > quote your output data to the nearest tenth as well. Anything beyond that is
    > just random garbage.
    
    Point well taken.  If I recall the concept of "significant digits" is
    centuries old (not that I am up to that math level yet ;-)  Determining when
    to round, and how many places to carry forward when using a handheld
    calculator or computer application for computations is a work in progress
    for me.  If I recall correctly, Alex informed me that a significant digit
    can be added in division of a ten figure average--but that does not apply in
    this case.
    
    All I can accurately state; when someone I respect sends me refraction
    correction figures to 5-or-so places I respond in kind. Much like the story
    of the daughter that asked her mother why she always cut the end off the
    roast before putting it in the roasting pan/oven.  Mom replied, "That's the
    way I learned it from my mom." So they phoned the daughter's grandmother and
    asked her.  Grandma replied, "because my pan was always too short for the
    roast." 
    
    Bill wrote:
    
    > And:
    > "Regarding my question, "Another hypothetical scenario.  If I take the  same
    > two stars, calculate true separation of 34d 27.7', they have identical  Hc's
    > of 1d 36.8', and  hypothetical refraction is -88d, what separation  might I
    > expect to measure with a sextant?"
    >
    Frank responded:
    
    > I didn't respond to this before because I cannot for the life of me figure
    > out what you're getting at. If you have two stars with an unrefracted distance
    > of 34 deg 27.7' and you observe them down at 1.5 degrees altitude, then the
    > measured distance will be very close to 34d 27.7'. What's this "-88d"  number?
    
    Perhaps I misstated.  Their true/calculated, unrefracted altitudes are
    nominally 1.5d above the terrestrial horizon.  (A value I chose as the
    center of the sun can be almost -50' true/Hc altitude and still have the
    upper limb visible, and if I recall list postings stars extinguish near the
    terrestrial horizon, how near I do not recall--so left a little leeway as I
    did not want to muddy the waters with technicalities.) The theoretical
    refraction figure of -88d was proposed to test my understanding of movement
    up the triangle sides, as well as limits of the refraction-separation
    formula. (I acknowledge this refraction value is *way*  outside physical
    reality as Earthlings experience it -- but it is sometimes useful for me to
    reduce an argument to the extreme/absurd.)  Sorry for any confusion.
    
    My assumption was that given the above *theoretical* scenario, the stars
    would be lifted up and towards the zenith by 88d (up the triangle sides,
    straight or arcs ;-) and therefore be *observed* as being close to 0d apart.
    
    Bill
    
    
    

       
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