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Greg,

Your location is further off from the true location than what I would
have expected from this photo. Comparing the results for the true
location with what you measured in the photo corresponds to an error
in sun height of 10 pixels. I think the photo is somewhat better than
that. You also selected the LL which is more critical relative to
refraction. My measurements of the photo result in 6 pixels difference
for the LL and in 3 pixels for the UL. It could however well be that
you didn't put the same effort in measuring the photo than what I do
when I enter those in my database. For this the pixels of each of the
four limbs (left, right, upper and lower) are measured four times,
using then the resulting mean values. The difference between measured
and expected diameter indicates whether the positions of lower and
upper limb have to be corrected for over exposure or under exposure.
The apparent horizon is measured four times together with the upper
limb and four times with the lower one. This picture actually also
shows that quite often the apparent horizon is more difficult to
measure than the sun. The sheet "Measurements" in the attached Excel
file shows the values which I extracted from the photo. The sheet
"Locations" in this file shows how the (estimated) locations were
found by trial and error. For this I assume a location and calculate
the apparent height of the sun, this until I find one having a
reasonably small difference. I also attach a screen shot from Google
Earth showing our results and the location from where the photo has
been taken.

Marcel

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