|
Hello Tracy,
For an usual analemmatic dial an analemma
around the central scale of date is not suitable for correcting the time with
the value for equation of time if it isn't noon.
For other times the analemma is just a table to
read the value of the EoT.
For such a reason you may draw the analemma of
course but don´t use it for correct time reading, except at noon.
But there are possibilities to have an analemma on
your dial that will work, however it is an approximation.
Split the dial into a morning half and an afternoon
half.
Each part get´s its own analemma.
So you have a dial with two
analemma´s.
Such dial may be calculated with a program by
Helmut Sonderegger, Austria.
An example is attached.
You see that the shape of the analemma´s is a
liitle changed but still they are analemma´s.
There is a small error in the readng but
for sundial it is still a good reading you
get.
Best wishes, Fer.
Fer J. de Vries
Eindhoven, Netherlands
lat. 51:30 N
long. 5:30 E
----- Original Message -----
Sent: Sunday, October 29, 2006 10:52
PM
Subject: date scale
Hello Everyone
I really like the drawing you made John for your
customers - it helps a lot. Thank you.
Thanks Tony for the picts and Powerpoint presentation -
it is wonderful.
Thanks Chi-Lian and Linda for your
comments.
After reading the advice I have received, I think that I
will make my date scale the conventional way - although I think the analemma
looks way cooler! It looks as if the first day of summer and the first day of
winter are at each end of the scale. Is this true always? Also, does one stand
directly on the centerline, or on the month "block" which falls to the left
and right of the center line?
More on my previous obsession of using the figure 8 in
the date scale:
If I am not mistaken, an analemma, on the ground for
instance, can be made by marking the position of the sun (cast by some point)
at the same time for a year every few days or so. I am referring to the
website: http://www.cerrilloshills.org/analemma/path3.htm So,
if I were to mark the path at noon, local time, for a year, the figure 8
should fall on the N-S line? It appears as though the months outlined on the
figure 8 match the date scale in placement except at the top portion of the
figure 8 where the months seem to flip from the left side to the right side. I
can't help but think that the straight line date scale mimics the analemma in
month placement. That's why I figured that I would make the figure 8 instead
of the plane straight line. Also, I thought about positioning some type of
gnomon that would cast a bright spot (or shadow) on the date scale which could
follow the figure 8 path exactly (at noon) just like the noon analemma sundial
featured in the website above.
I am fascinated by the analemma and would love to
somehow use it in my sundial, however, I definitely want my sundial to be
correct and accurate - no false sundials here! But I keep seeing the analemma
used as a date scale in pictures on the internet. One I found looks like it is
bronze.
If I shouldn't use the analemma in the date scale, where
could I put it in the sundial properly? Or, should I just make a separate noon
analemma sundial like that in the website referred above?
---------------------------------------------------
https://lists.uni-koeln.de/mailman/listinfo/sundial
| 
Image1.gif