Hello Frans, and sundial list members --
Thanks for your interest.
I apologize for any confusion caused by my use of the phrase "for use
with straight hour lines." The words were mine, not John Close's, and
I guess I was trying to reinforce his desire to have a polar dial
which didn't use wavy hour lines, whether the lines looked like 8's
(full analemmas), S's (half analemmas), or stacked S's (unfolded
analemmas).
I suggested to John that if for civil time he wouldn't use wavy
lines, he might pivot his dial around an axis parallel to the
Earth's, changing the dial's facing direction slightly every day (or
every few days) to account for EoT. Some dialists feel that a pivoted
polar is no longer a polar, but that's a different problem, for
"polar dial" seems to have some different meanings, depending on what
source is consulted.
A 3-D gnomon on a polar dial would cast a wavy shadow on the flat
dial plate, and civil time could be read where that shadow crossed a
straight line of hour points. That is, if a suitable 3-D shape is
possible. Some think yes, some are skeptical, some say no. At the
moment, I'm in the skeptical group. What do you think?
So that's the question--can a 3-D gnomon be designed for a "normal"
polar dial to give civil time where the gnomon's shadow intersects a
straight line of hour points? If yes, what does the shape look like?
If no, why not?
Best wishes,
Mac Oglesby
P.S. Bill Gottesman has sketched a possible solution and has given
permission to share. Contact me OFF LIST if you want a copy of his
drawing (16K gif).
P.P.S. Looking a a current list (today's) of members of the sundial
list, it appears that John Close still needs to be cc'd at "John
Close" <[EMAIL PROTECTED]> [period]
Hi Mac and all,
I am afraid I don't quite understand the question. John would not like
analemma shaped hour lines, you wrote. How might figure-8 shaped hour lines
be used here??
One can simply incorporate the EoT into the hour lines of a common polar
dial as a function of date, running from January to December. No figures-8,
just somewhat wavy lines. And a date scale, of course. If one would manage
to make a wavy gnomon, one gets a wavy shadow falling on straight hour
lines. Not much of a difference, I would say. And one would also need a date
scale to read the time.
So what is the question actually?
Regards, Frans
53.1N. 6.5E
----- Original Message -----
From: "Mac Oglesby" <[EMAIL PROTECTED]>
To: "Sundial Mail List" <[email protected]>
Cc: "John Close" <[EMAIL PROTECTED]>
Sent: Monday, December 09, 2002 3:21 PM
Subject: 3-D gnomon for Polar Dial
>
> Hello All,
>
> John Close has posted this message on the NASS Message Board:
>
> "Does anyone have any ideas for a Polar Dial which allows for an
> Equation of Time adjustment. I would not like analemma shaped hour
> lines as I think this would detract from the simplicity and
> minimalistic quality of a Polar Dial. I am told an analemma shaped
> gnomon for a polar dial would be hideously complicated and probably
> not work . Any ideas anyone? John Close"
>
>
> John has discussed this problem with several members of this list,
> including me, Bill Gottesman, John Davis, and Pete Swanstrom. Some of
> us think that a 3-D gnomon could be designed for use with straight
> hour lines to correct for EoT, and some are skeptical.
>
> Please share your comments and suggestions.
>
> Best wishes,
>
> Mac Oglesby
>
> P.S. Since I do not know if John Close is a member of this List,
> please cc to him.
> -
>
-
-
