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Alex,

Even with that bad point in there your mean is -0.2' from the truth
with a standard deviation of 0.7', and a standard error of the mean of
0.3'.  Usable.  To the best of the knowledge that has been posted here,
the standard deviation of lunars is about 0.2 to 0.3' of arc.  It would
seem that an excellent observer under good conditions could get it to
about 0.15' or less, rarely better, based on what I have heard about
altitude shots in artificial horizons and achieved a few times.  With
the bad point removed your observations were off by 0.0' with a
standard deviation of 0.36'.  That's pretty good.  Maybe a bit better
than George's seemingly grudging, 'It was Alex' lucky day.  With
shooting like that, the standard error of the mean would be 0.16', so
many shots should be pretty close to the mark, given an accurate
sextant.

Given good equipment, I think Frank may be right that lunars aren't all
that difficult, except perhaps calculation by table using any method
other than Bruce Stark's.  It looks like you made the right choice
getting that snowy sextant rather than a Husun.  The main problem is
the inherent limitations on accuracy and precision.

I think plotting distance versus time would give one an assessment of
precision.  Accuracy would be tougher to assess at sea, and would
depend mostly on the calibration of one's sextant and its freedom from
perturbations.

Fred

On Oct 25, 2004, at 5:09 PM, Alexandre Eremenko wrote:

> Dear George,
> Thank you for finding the misprint in my table,
> and for your other illuminating comments.
> (I was surprised myself that averaging of such "so-so"
> observations miraculously gave zero error).
> I am posting the corrected table, including the
> rejected "blunder" observation which was not included in
> my earlier posting.
> Please notice: it was rejected BEFORE any reduction.
> I would always reject such an observation.
> I am waiting for your opinion whether my procedure was sound or not.
>
> AP: N 40d27.2'  W 86d55.8'
> GMT: 4:00 Oct 24, T=58F Pressure 29.75
> Observation from my balcony, height 12ft,
> Sextant SNO-T, index correction 0.0', inverting scope.
> One of the 6 observations (column 4) was immediately rejected
> because it did not follow the pattern of increasing
> distances. I reduced with Frank Reed's on-line calculator.
> First, each measurement, and then their average.
> The third line is the error in the distance, the fourth line
> is the error in the longitude:
>
> Moon-Altair:
>
> GMT   4:06:49    4:09:58     4:13:10  4:14:58   4:17:12    4:18:57
> DIST  51d22.2'   51d23.3'    51d23.8' 51d22.4'  51d24.1'   51d24.3'
> ERD       0.0'      +0.5'       +0.3'    -1.5'     -0.2'      -0.4'
> ERL      +0.3'     +13.5'       +8.7'   -44.0'     -7.3'     -12.2'
>
> After the rejection of column 4:
> AVERAGE GMT: 4:13:13  AVERAGE DIST: 23.54'
> ERROR IN DISTANCE: 0.0' ERROR IN LONG: 0.4'
>
>
>> It was Alex's lucky day.
>
> I understand this is not a compliment:-)
> I will try to repeat it today, thank God, the weather is
> perfect.
>
> Alex.
>

   

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