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From: Mike Hannibal (no email)
Date: Fri Dec 09 2005 - 05:34:57 EST
Frank,
thank you for your positive words. I tried another set last night and experienced just what you suggested - two orders of error. I suspect that there is a quite practical reason as you suggest. My wife who knows me best suggests that last night it was brought about by my concern that I was about the lost Venus behind the house next door. This house is a half storey higher than my perch and Venus was mighty close to its roof.
I will report my next set and see where I'm up to.
Regards
Mike
Frank Reed <> wrote: You wrote:
"Site # Error in Lunar Error in Lon
2 0 min -0.8 min
3 -0.4 min -11.6 min
4 -1.3 min -37.5 min
5 -0.2 min -7.3 min
6 -0.1 min -2.0 min
7 0 min -0.3 min
8 -0.7 min -22.6 min
From this I deduce a number of things. Firstly if my
interpretation is correct I have a consistent tendency
to not quite bring the bodies into tangency. This
would be borne out by my sense that I had to try to
bring things closer and that the bright "penumbra" for
lack of a better word - around the moon caused me to
prematurely assume tangency. Secondly I am horribly
inconsistent.
Does anyone have suggestions about judging tangency?
Any other suggestions - other than practise - to
improve matters."
Apart from the 1.3' error, these are EXCELLENT results, and you should be
very pleased with them. If the approximate standard deviation of your lunars is
0.2 arc minutes or so, you're doing very well. Don't worry so much about the
error in longitude. That's intrinsic to the method of lunar distances. If
you could get angular altitude measurements, as opposed to lunar distances, as
accurate as this for ordinary LOP celestial navigation, the error in position
(longitude, if the object is bearing east or west) would be the same as the
error in observation, in other words less than 0.2 nautical miles, in most
cases.
So what about that 1.3' error? I find in my observations, that the errors
seem to come from two sources. There is a seemingly irreducible scatter of
observations with a small error and then there is a secondary source of error
that's quite a bit larger and more common than I would expect from the
distribution of the "small" error. Another way of putting this is to say that the
error distribution has "fatter tails" than the expected normal distribution. That
second source of error might be something as simple as a hand tremor that
develops with fatigue. Varying your procedures --taking breaks, holding the
sextant differently-- might remove those larger errors. But that's just a
guess... Could be anything!
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
Send instant messages to your online friends http://au.messenger.yahoo.com
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