Hello Arthur,
While it is true that at a given solar declination one could mistakenly
read the "wrong side" of an analemma it is quite simple to add guide
arrows along the analemma to indicate the direction the sun is currently
traveling, e.g., with the sun in the winter months the analemma is read
along the portion indicated by the first set of rising arrows (sun). In
fact, this is exactly what Dan has incorporated into his dial, quite
beautifully too. I chose a somewhat different approach, I use colors to
"break" the analemma into its respective seasonal segments (see my WWW
sundial generator). Most people know what season it is (we hope!) and
that is enough to make the correct reading, i.e., knowing the date is
not necessary. Regarding accurate mean time reading during the period of
the solstices (when the rate of solar declination is slowest) I have
found that projecting an image of the solar disk onto the analemma is
best (moving parts though).
Best,
Luke Coletti
Arthur Carlson wrote:
>
> Daniel Lee Wenger <[EMAIL PROTECTED]> writes:
>
> > The reading of standard time via a sundial may be accomplisted by
> > mearly reading the declination of the sun and using an analemma,
> > determining standard time. At no point is the current date needed to
> > do this.
>
> Way, way back I explained why I was not totally satisfied with this
> method, essentially because there are (almost always) two values of
> the EoT for each value of declination. At the solstices there are
> even an infinite number of values (in some technical sense).
> Consequently, if you are interested in relating the sundial reading to
> clock time, you always need some knowledge of the current date.
>
> Art Carlson
