Daniel Lee Wenger <[EMAIL PROTECTED]> writes:
> On my globe the significance of the analemma is apparent. Each analemma
> represents the geographical
> position of the sun at mean time 6, 7, 8, 9, etc. for each day of the year.
> In fact the geographical
> postions of the sun at those mean time hours would be a collection of 365
> dots but the analemma
> is interpolated to generate a semi continuous curve. Since the set of dots
> that would be generated during the following year would be slightly
> different the curve used represents some sort of average
> of the dots over a four year period.
The set of dots that would be generated during the following year would lie
on the same curve. The reason the dots are not in the same places is that
the year is not a whole number of days long. The curve is not an average
over a four year period. If you were to draw four years' curves separately,
you would see that the curves are identical, but the points used to plot
them are not. The curves are the graph of Equation of Time against
declination, both of which are functions of the solar longitude. The
particular values of solar longitude at, say, noon every day in 1999 are
different from those in 2000, but the analemma points lie on exactly the
same curve (ignoring only very long-term drift).
To use straight lines as an illustration, the points (1,100) and (6,105) lie
on the same line as the points (2,101) and (7,106) or the points (3,102) and
(8,107) or the points (4,103) and (9,108).
Chris Lusby Taylor
Email: [EMAIL PROTECTED]
(Formerly [EMAIL PROTECTED])
