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    Re: Mike Burkes' observations.
    From: George Huxtable
    Date: 2003 Jul 29, 00:37 +0100

    Mike Burkes wrote-
    >statement" surface tension effects distorting liquid from being plane and
    >level" is most plausible explanation for discrepancy.
    My response to Mike-
    Be careful not to jump to conclusions. Are you certain that the two fluids
    in your artificial horizon are indeed immiscible? If they mix, then as I
    see it such a "plausible explanation" would be quite impossible. It would
    be useful to make some further tests with those two fluids before deciding
    on an answer.
    Even if the fluids remained in the pool as separate globs, I question any
    effect such as Mike conceived in his first mailing- "I feel the reason for
    the discrepancy stems from the
    artificial horizon fluid being a combination of baby and bath oil
    introducing a constant error." I can see no way that such a non-mix could
    "introduce a constant error". If there were patches at the surface, of
    different fluids, then the surface-tension effects might randomly perturb
    the measured altitudes, perhaps, but not "introduce a constant error".
    Mind you, to explain the effect that he has noted (that of a reasonably
    small overlap zone between his four position lines, yet a displacement of
    that zone by 20 miles to the West), Mike should not call for a "constant
    error". Instead, any liquid-level distortion must be tailored suitably to
    the azimuth of each of the four measurements, to get just the right
    Westward shift for them all. Might the surface of the artificial-horizon,
    in each case, be randomly (and differently) distorted by just the right
    amount? Well, it's possible, but seems unlikely to me.
    Mike goes on to say-
    >Chronometer error
    >would have been logical choice for Longitude discrepancy however the Lunar
    >LOP and Lunar distance results eliminate that.
    How do the Lunar LOP results eliminate that? I don't see why. Explanation,
    The lunar distance results don't eliminate it either. Lunar distances are
    not a sufficiently precise measurement of GMT. Mike's lunar (which I
    haven't checked in any detail) gives the excellent result of a discrepancy
    with GMT of only 7 seconds, but this remarkable agreement must be, to some
    extent, fortuitous. To explain the odd position lines, we're looking for a
    discrepancy in time of around 80 seconds. A change in time of 80 seconds
    implies a change in lunar distance of about 40 arc-seconds only. I don't
    think even Mike Burkes, for all his undoubted observing ability (more on
    that later) will claim that he has measured and corrected the lunar
    distance to within a fraction of that 40 seconds of arc.
    >For now I will stick to poor
    >artificial horizon liquid choice reason for error and in future use ONLY
    >homogeneous liquids!
    I counsel caution about the first part of this sentence, but agree fully
    with the last part.
    I have picked out Mike's run of four Sun-lunars, as follows-
    >Sun is Lunar Dist. body.
    >Data: Four obs:
    >GMT 20-53-15, 20-58-35, 21-02-40, 21-03-30,
    >corresponding Ds: 61d 32.2m, 61 34.3, 61 36.0, 61 36.3.
    >AP for Hc"s: 34d 24.0N, 119d 02.0W.
    >Sun Hc=74d 36.5m,Moon Hc= 37d 30..5m.
    >C.E.Fast 12m 25s,July 04,
    >cleared dist"D" as per Stark book=61d 23.0m, resulting in GMT error of 00m 07s.
    I have plotted out the four lunar distances against time, and recommend
    that others do so too. They are a superb fit to a straight line, with
    hardly any scatter. This shows that Mike has the necessary sharp eye and
    steady hand, and the coordination between them, for a really good lunar
    observer. I suspect he is no novice at this game. Of course, that plot does
    not demonstrate the absence of systematic errors, but it shows that his
    random errors are consistently very small indeed.
    I'm a bit worried by his four stated timings, however, which he quotes as
    "GMT 20-53-15", etc. The averaged time, if treated as GMT, does not
    correspond with the calculated altitudes for Sun and Moon. So I suspect
    they are not GMT, but clock time, and that's why he has provided a figure
    for clock error on GMT of 12m 25s fast. Allowing for that clock error, then
    the altitudes come out much better. Is that the right way to treat this
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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