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Ken Meldrew has been very inventive in speculating about different possible
errors that might have been made in those Lewis and Clark lunars. And even
considered a combination of two possible errors. I'm sure this is the right
attitude to take. If there was an observational blunder that it was
possible to make, you can be pretty sure that at one time or another L&C
will have made it. There most be SOME explanation for that strange data-set
of Dec 2-3 1803!

His first speculation was that he had found the mystery star which had the
right coordinates to correspond with the measured distances, supposedly to
"Aldebaran". Already, we have established roughly how much out-of-line with
the Moon's track (to one side or the other) a star would have to be so that
the same star could possibly fit both sets of observations, A and C. And
then, we have to search those two segments of sky for a star that's just
the right distance from the Moon.

Well, there's such a plethora of stars in the sky, that there must be many
that will fill the bill, but the question is: is there a bright and
prominent star, that could have been mistaken for Aldebaran? However, the
only one Ken has been able to come up with so far is magnitude 4.5, and
Frank Reed has pointed out that such a dim star could hardly have been seen
in the sextant, let alone mistaken by Aldebaran, not even by L&C. I agree
with that view, and now Kan Meldrum has acknowledged it too.

Next Ken proposed that the sextant may somehow have been set to an angle
exactly 15deg less than was intended. Then, as Frank has suggested, casting
around the sky for a bright star at that wrong angle from the Moon,
Betelgeuse would become the obvious candidate.

But why should the sextant have been set to exactly 15deg in error for
observation-set A? And then, set to some new value, for observation-set B,
of "Regulus", which so far we have not considered in detail. And then set
again exactly 15deg in error for observation-set C. This is not a single
accidental error, it's a recurring error. What might cause the 15deg
displacement?

I thought that the answer might perhaps be found if, in error, the required
angle had been set against the wrong end of the vernier scale, if that was
just 15deg wide; an easy mistake to make. However, with a sextant divided
to quarter-degrees, and a vernier reading to quarter-minutes, as this one
seems to be, I presume that the vernier scale would be marked 0 to 15
(minutes), but this would have to span a length on the main scale, not of 0
to 15 (degrees) but 0 to 49 and three-quarters. Or perhaps 15 and a
quarter; either should work. Can anyone, such as Henry Halboth, with an
instrument calibrated to 15 arc-seconds to look at (which I don't have)
check that this view is correct, please. If so, setting the degree scale at
the wrong end of the vernier would give rise, not to a 15 degree error, but
one that differs by from 15 degrees by all of 15 minutes. Quite enough to
destroy that otherwise-attractive hypothesis, I'm afraid.

So I am still unconvinced about the suggested scenario: that the sextant
angle was set 15deg too small, on two separate occasions, and then
Betelgeuse was substituted for Aldebaran. I can accept that the second
might follow from the first, however. Can anyone offer further persuasion?

However, I applaud the ingenuity that has been shown so far, by all
concerned, and thank them for their continuing interest in what appears to
be a fascinating, if intractable problem.

Henry Halboth asks if it might be possible for the error in the lunars
could result from measuring to the wrong limb of the Moon, and the answer
is "no. it isn't possible". A limb blunder could give rise to an error in
lunar distance of about 0.5 degrees, not much more. We are trying to
explain an error of somewhat over 1deg, for obs. A, and well over 1deg for
obs. C.

George.

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01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
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