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The way you describe the way you took the shot, overlaying the two
images, means you measured the altitude to the center of the sun, not to
either limb. When you measure to the center of the sun (as is the norm
with a bubble sextant) you must not make a correction for semi-diameter
when you make the corrections to the sextant altitude. If  you made the
corrections with the tables in the Nautical Almanac then you
inadvertently included the semi-diameter correction which is built into
the N.A. sun correction tables. To avoid this problem with a center
observation simply use the correction table for stars which is simply
the refraction correction and doesn't include a semi-diameter component.
Since the semi-diameter correction is 16 minutes it seems likely that
the error you ended up with might have been caused by improperly
applying the semi-diameter correction.

You should have gotten a lot closer so I suspect that you also have an
index error so you need to determine that and then recompute.


Andrew Corl wrote:
> All,
>
> I want to thank everyone for the advice and support.  I took my little
> artificial horizon our this evening and got everything lined up.  Took
> a sun sight but overlaid the images of the two suns (did not know to
> have the limbs touch).  I did go online to Celnav.de and used
> Henning's sight reduction program and was within 22 miles of my house
> lat and long which I measure using a GPS.  I WAS THRILLED!!!! Now that
> I know how to do this I will probably practicing on a regular basis.
>
> Again thanks to everyone for your help and guidance.
>
> Andrew
>
>
>
> ------------------------------------------------------------------------
> *From:* Bill Morris 
> *To:* NavList@fer3.com
> *Sent:* Thu, September 2, 2010 4:24:00 PM
> *Subject:* [NavList] Re: Using an artificial horizon
>
> glapook wrote:
>
> "Lining up the bottom edge of the
> sun's image in the index mirror with the top edge of its inverted image
> in the liquid gives you a lower limb observation."
>
> This is something other advisors seem to have missed. Always line up
> the edges(limbs) of the sun's images. Trying to superimpose one on top
> of the other is more difficult and less accurate, though if you did
> get it right, you would not then have to apply a correction for
> semi-diameter.
>
> I began practice 30 years ago using the reflection off the surface of
> a swimming pool on a calm day. It worked at night too with stars, and
> made identification of images easier, given the wide "field of view".
> I graduated to old sump oil in a roasting tin.
>
> Bill Morris
> Pukenui
> New Zealand
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