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From: Bill (no email)
Date: Wed Apr 20 2005 - 01:25:54 EDT
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." <G>
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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