Hi Fritz,
The analemma is in essence just a graph of the EoT vs Declination, in
discussing the components of the EoT the analemma need not be mentioned,
the analemma is just another way of expressing the EoT. The dynamics of
the EoT define the shape of the analemma.
As regards to the EoT not being dependent upon obliquity, I'm not sure
what to say, other than it truly is. I can say that you are correct in
saying that some value for the EoT would still exist if our axis of
rotation was perpendicular to the plane of our orbit (zero obliquity),
assuming that there is still eccentricity to the orbit.
Also, the analemma fundamentally needs no correlation to date. The
single solution you mention has to do with orbital position not the
date. However, many (like me) include the date along the analemma and
the short term variation of the leap year cycle will effect the
placement of the "date ticks".
As regards to the variation of the EoT (changing shape of the analemma)
requiring 26,000years, this too is incorrect. I've explained this in
some length in earlier messages to the list. In short, the rate at which
the Vernal Equinox approaches perihelion is approx. 50arc-secs/yr and
the rate at which perihelion approaches the Vernal Equinox is close to 7
arc-secs/yr with a delta close to 1arc-min/yr! For example, the shape of
the analemma was symmetrical in the 16th century, is it symmetrical now?
Hmmm, what happened? Was the 16th century 26,000 year ago?
Regards,
Luke Coletti
Fritz Stumpges wrote:
>
> Luke, I really liked your clear explanation, but I think you meant to say
> the ANALEMMA has two components, the EOT and the declination. The EOT is
> not dependent upon the obliquity; we would still have it even if the axis
> were perpendicular to the ecliptic. Luckily, both independent components
> have a common, cyclical variable, the time of the year, and therefore have
> a single solution graph. Like you said, can you imagine the changing
> analemma if precession were only 100 years instead of 26,000 or so years!
