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Arthur,

Thank you for responding.  This interchange of data and calculations
is surely increasing my understanding of lunars, and I was very glad
to hear it was increasing yours also.  I was particularly struck by
the difference between the hourly rate of change in observed and
apparent distance, and the role of the various factors in this.  I
see that I have to think on this more.

Regarding whether the lunar GMT being fast of the actual was due to a
gap in contact or an overlap, I still believe it was a gap.  The
basis for my reasoning follows: the distance between the moon and sun
was increasing with time.  If the time reported was 4:05, for
example, rather than 4:00, which is the situation, this would imply
that a greater distance was recorded than actually occurred.  A
greater distance leads to a gap.  If the distance had been decreasing
with time, than a fast time would have been due to an overlap.  I
almost had myself talked into the reverse thinking after reading your
post; this is tricky.

Regarding gaps, I have been measuring index error by observing the
semi-diameter of the sun, which is a fairly easy measurement, since
the sun doesn't move relative to itself!  It is only lately that I
have not consistently been getting a 0.1' overlap in each
measurement.  Now I know this isn't 1.5', but....

I think when we see the errors in our computations, we have to
remember that most of us are not making these measurements and
computations on a daily basis, as would be the case for a navigator
at sea.  I'm sure daily repetition would help.  Additionally, I think
the need actually to have to depend on the results would sharpen
one's abilities, perhaps acutely!

Fred

   

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