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From: Frank Reed (no email)
Date: Fri Dec 09 2005 - 02:24:05 EST
Bill you wrote:
"If you are not presetting to the the approximate
separation, getting an initial rough alignment can be difficult. For stars
at sea, some texts recommend inverting the sextant and viewing the star
directly while moving the reflected horizon (much easier to see) into
approximate position. Then flip the sextant and go for final alignment."
Which raises a question, why flip it for the final alignment? Partly it's
just less awkward, but it also highlights those two different methods of
swinging the arc.
And:
"An observation: Frank's site rounds observation (lunar) error in 0.1'
increments. If I recall, Frank stated the error in longitude was simply the
observation error times 30. Since the errors in longitude are not multiples
of 30, I would guess they are calculated prior to rounding the observation
error. In which case, if you want to be really anal, divide the longitude
error to get the actual observation error before rounding. For example, one
of my observations showed -0.2' observation error and -5.0' longitude
error. -5.0/30 = -1.67, better than the -0.2 would indicate. One -0.1
observation error showed a -4.4' longitude error. -4.4/30 = -0.147', so not
as good as -0.1' would indicate."
But remember, the clearing calculation can be no more accurate than the
altitude corrections. The refraction is no more accurate than the nearest tenth
of a minute of arc, so that's all there is in there. Dividing the longitude
error by 30 may "look" more accurate, but those extra digits are just junk
data. I think I should probably drop this "cheap" longitude error correction
completely.
And:
" I warmed up the car while doing the observations,
then brushed the snow off and scraped the ice from the windows before I went
out to stock up on food and beer before the temperature became sub 0 on both
the F and C scales."
Hah. Myself, I'm hoping for a "forty below" this winter so that I can be the
only guy in the room who knows that it's the same temperature on both scales
<g>.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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