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From: Alexandre Eremenko (no email)
Date: Tue Apr 19 2005 - 20:59:42 EDT
I am still struggling with my SNO-T, trying to determine
any instrumental error from distances.
(Once George asked: "Did anyone succeed in determining
instrumental error of a modern sextant by ordinary observations"?
I cite from my memory: still cannot manage the search engine
on this list:-(
I think I did. My SNO-T sextant has a certifricate, which is
filled by +10" everywhere on the arc. But even the seller
confirmed that in the last years of Soviet Union, no one
really cared to measure and they filled the certificates with
random numbers (even did not care to vary these numbers:-)
Anyway, here are the result of my last distance measurements
as they are. I will appreciate any interpretation of these numbers.
Index correction. Always from 0 to -0.2', since October 2004.
I do it every time when I do observations. From the Sun
or from the stars. The results are consistent.
All distances I mention are
measured under
ideal conditions from my balcony in perfect weather.
Lunars are reduced with Frank's calculator, star distances with
my own computer program. A light filter is frequently used on the
moon at night, an appropriate one on the Sun,
and no filter on the stars.
April 19
2:00 GMT, 8 measurements of Sirius-Procyon,
standard deviation 0.15', maximal span 0.4',
distance approx. 25d40' average error +0.5'
2:20 GMT, 7 measurements of Procyon-Capella,
stabdard deviation 0.2' maximal span 0.6',
distance approx. 51d7' average error +0.4'
Same with Galileo scope, average error +0.3'
2.37 GMT, 7 measurements of Sirius-Capella,
standard deviation 0.3' maximal span 0.5'
distance approx. 65d48', average error +0.6
22:45 GMT 8 measurements of Jupiter-Saturn,
standard deviation 0.3', maximal span 0.5'
distance approx 81d53', average error 0.0'
23:30 GMT 6 measurements of Sun-Moon distance,
standard deviation 0.2'
distance approx 127d10', average error +0.8'
This is just a sample. My log book is full of similar data,
and they are consistent in the average,
produced since October 2004. Can anyone help me to
interpret this?
(In the beginning I thought that this is my technique
to blame, but now (after having tried once Bill's new
Astra III) I begin to suspect that this is an instrument error.
a) it is ALWAYS positive.
b) it ranges from +0.2' to almost 1'.
c) Sometimes it is almost zero, but rarely.
Based on the recent observations I can make the following table
of corrections:
25 38 51 65 68 71 82 90 127
-0.5 -0.4 -0.4 -0.6 -0.2 -0.1 -0.2 -0.2 -0.8
Should I attach this table to my sextant box lid as a
certificate, and use it?
Any comments?
Alex.
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