NavList:

Well George,

At least our results agree.

But I think you need to go back and read my original post. For ease of
reference, I shall quote the pertinent passage:

"Ok, Ok, I know that a bubble attachment is simply not as reliable as a true
horizon and that 8 observations do not constitute a statistically-correct
defence to support my assertion about the inaccuracy of moon shots. I merely
presented these data to illustrate what has been my experience since I first
picked up a sextant 23 years ago. It is more often than not, the same for
me: to borrow from the modern pop culture vernacular: moon shots simply
suck. At least for me."

George's conclusion can be summed up as follows: the idea of the moon being
an unreliable object for observation is ancient mariner's folk wisdom and
therefore should be dismissed outright. If this conclusion is based on
George's personal experience, I say: "fair enough". Each of us to some
extent, lives within the reality we create (this is not intended as a slight
by the way).

But George's detailed discussion about his analysis of my sights, appears to
be the basis upon which he draws his conclusion. On the one hand, George
agrees with my original statement that there is not enough data upon which
to base a conclusion. Refer to my original statement. But I did not stop
there: I was careful to point out that I was offering these data to
illustrate what has been my experience with moon shots from day one: more
often than not, I simply do not get good results with moon shots. George
appears to have overlooked this portion of my statement.

While George agrees that there is not enough data upon which to base a
proper statistical analysis, he is able to surmise that there is some kind
of systematic bubble/sextant index error present. George old buddy, you
cannot have it both ways. There is either enough data upon which to base
conclusions or there is not. In my original statement, I stated
unequivocally, that there is not. At no time, did I attempt to use these
data to support my original suspicions about the unreliability of moon
shots. I do not believe that they can be used to determine index/instrument
errors either. Especially because they were taken with a bubble sextant
which is a fickle device and subject to errors.

I will throw a little curve ball at you: earlier in the day, or shall we say
the previous day, if we go by GMT (7 hours prior to the Moon-Vega shots), I
took four observations of the sun. The average result for the 4 observations
was 0.7 arc minutes away. Same sextant, same bubble attachment. Furthermore,
I should add, the bubble attachment has been calibrated and there should be
no inherent errors in the instrument.

Does this prove that moon observations are unreliable?  Does it support my
case? No. Certainly not.

This could go back and forth forever. I am going to do a bit more research
on this myself and get back to the list with my findings, if any. I may
start by asking other mariner friends if they are of the same mind vis a vis
moon observations and if so, why. Regrettably, I can offer no scientific or
statistical proof one way or another. I can only go by my own experience. If
I were lost and had only a moon shot to go by, I would be deeply suspicious
of the results and would eagerly await the appearance of another celestial
luminary to lead me to safety.

I am heading out on my boat for a few days for some hunting, fishing, and,
if the Gods smile upon me, some clear sea-horizon sextant observations.

I can pick up this thread upon my return.

Robert


----- Original Message -----
From: "George Huxtable" <george@huxtable.u-net.com>
To: <NavList@fer3.com>
Sent: Tuesday, August 22, 2006 7:38 PM
Subject: [NavList 1119] Re: Moon altitude problems.


>
> Robert Eno has lindly sent me, off-list, the original data, taken with
> a bubble attachment to his sextant, on which his conclusions about
> errors in observing the Moon were based.
>
> I can confirm that my own analysis gives the following results-
>
> Four observations of Vega; The recorded altitudes were lower than they
> theoretically should have been, by 2.7, 0.3, 0.2, 1.9 arc-minutes.
>
> Four observations of the Moon. The recorded altitudes were lower than
> they theoretically should have been by 4.0, 4.5, 4.4, and 3.8
> arc-minutes.
>
> There isn't enough data here on which to base a proper statistical
> analysis, but we can guess at a few conclusions-
>
> In skilled hands, such a bubble attachment is capable of giving
> remarkably good results; much better than I had expected, anyway.
>
> Robert Eno is indeed making his corrections properly (or at least, in
> the same way that I am).
>
> The Vega data indicates that there's an "index error" of the bubble -
> sextant combination, in which it tends to read low by a bit more than
> 1 arc-minute.
>
> The Moon data shows up an additional error, in which the sextant reads
> lower still, by about an additional 3 minutes. In the light of our
> previous discussion, it seems to me that this could well be attributed
> to the problems of centring an asymmetric Moon within the bubble, when
> there's only half the circumference of the Moon available for use. I
> see no need to call in aid any presumed defects in the Moon as an
> observable object, based on ancient-mariners' folk-wisdom, but others
> may take a different view.
>
> George.
>
> contact George Huxtable at george@huxtable.u-net.com
> or at +44 1865 820222 (from UK, 01865 820222)
> or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
>
>
> >


--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---