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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

   

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