Hello sun dialists,
I have a question. As I said some months ago I want to calculate the earth's
orbital eccentricity, using my sun dial. I tried it in two ways. First I
followed the suggestion of Chris Lusby Taylor and used the Ptolemy model after
finding aproximate values for the vernal equinox, the summer solstice, the
autumnal equinox and now recently of the winter solstice. My observed values
had an error of about ten hours. Using these inaccurate values in the Ptolmy
model gave me an e=0,0173. Not bad but also not very good.
At the same time I used a formula, given by my friend Stan Ulens in which the
total EOT was split in a contribution EOT1 due to the angle made by the
ecliptica and a contribution EOT2 due to the eccentricity. After about 200
observations during 8 months, I got three weeks ago a mean value e= 0,01671!
However things started to go wrong after 13 december. The values of e in
december skyrocketed to e= 0,0378 and even e= 0,0414.
Who has done similar work? What are the results? Who can give reasons for my
rather bad experience in December? I can measure the solar altitude with an
error of about 1 minute and the solar time with an error of about 1 minute
Jos
[email protected]
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