Bill,
If you'd like to see a more graphical representation of these two
effects (obliquity and eccentricity) and their relatives weights, see
the following URL:
ftp://ftp.gcstudio.com/pub/sundial/sday_eot.gif
I too would recommend the Bernard Oliver (of SETI fame) Sky&Tel article
_The Shape of the Analemma_, it is well worth reading. In my last
message to Fritz I mentioned the last point the analemma was symmetrical
was in the 16th century, this is not correct, this is what happens when
you write from work without having the reference handy! It was indeed as
Oliver shows, at around 1250. I have attached a GIF image showing the
analemma as computed for 1246 and 2000.
I generated the data sets for years 1246 and 2000 using my WWW Solar
Calculator:
http://www.gcstudio.com/suncalc.html
I have posted both data sets on my ftp site at the following URL(s):
ftp://ftp.gcstudio.com/pub/sundial/eot_1246.dat
ftp://ftp.gcstudio.com/pub/sundial/eot_2000.dat
I would have to finally say that the determination of the EoT's zeros
came with its analytic derivation, most likely developed with some
completeness by Flamsteed.
Regards,
Luke Coletti
[EMAIL PROTECTED] wrote:
>
> I think Andrew James' explanation about the sum of two symmetrical curves
> (inclination and orbital eccentricity) may be exactly how the zero point for
> the equation of time was determined. There is a good article on this in Sky
> and Telescope, July 1972, pages 20-3 by Bernard Oliver. He breaks down the
> analemma into these two curves, each of which is appears to be symmetrically
> referenced around the zero point (EoT=0). He then demonstrates, as Luke
> Coletti points out, that these curves change over time, changing the overall
> shape of the analemma. He calculates that in 1246AD the analemma was a
> symmetric figure 8, with its intersecting point (where the 8 crosses itself)
> at EoT=0.
>
> Bill Gottesman
> Burlington, VT
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