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Dear Fred,
Thank you for examining my report.

On Sat, 13 Nov 2004, Fred Hebard wrote:

> > Sextant upright position:
> > Up     Low     Sum    IndEr
> >
> > 32.5   32.5    65      0.0
> > 32.5   32.4    64.9    -0.05
> > 32.4   32.4    64.8    0.0
> >
> > Sextant upside down:
> > Up     Low     Sum    IndEr
> >
> > 32.4   32.4    64.8    0.0
> > 32.5   32.6    65.1    +0.05
> > 32.7   32.3    65      -0.2
> >
> Alex,
> I don't understand from where you are drawing
> the conclusion that you
> have a random human error of 0.3' for the sun.

You understood it correctly:
I was talking about the SPAN (range) of the results in a series
of similar observations. For example, the first column
of the upside down series has span of 0.3'. The second
column has also span of 0.3'.
I agree it was somewhat incorrect to call it "random error
of 0.3". The random error of plus or minus .15 will give
such results.

> It would appear you are not very
> good at operating the sextant upside down,
> but quite proficient right
> side up.

That's plausible. Upside down position is somewhat less
convenient: the screw is on top etc.

> Measuring the sun's semidiameter with the sextant in various
> orientations does seem to be good practice for taking lunars.

Taking lunars themselves, as well as star-to-star distances
whold be even better practice. My purpose here was
to check the rigidity of my sextant.

> How about sideways or
> at a 45 degree angle?

Also tried. Norie (1828) recommends horizontal sextant
position when measuring the index error from the Sun when
the Sun is low (because the vertical SD and the round shape
of the low Sun
may be seriously distorted by refraction).

> By the way, I get numbers similar to your right
> side up measurements on
> dry land,

With what sextant and scope?

>but, thus far, they are much worse on the
>water.

Unfortunately, I have no possibility to go sailing,
at least until next summer.

I still have much less success with another exercise:
to determine my arc correction from star-to-star distances.
The results I obtain are inconsistent.
I mean the "span" is too large.

Alex.

   

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