This has all been very instructive. I am not a complete beginner, but have
to confess that I was under the impression that rotating the dial plate with
respect to the fixed gnomon was sufficient. Somebody once told me I could
do this and I never really thought about it. If you actually think about
the longitude correction, it does become obvious that just rotating the dial
plate is not going to be right.
For any dials I have made, I either used one of the programs like Shadows
Pro or Orologi Solari to include a longitude correction, or more
frequently, now, I use a delta cad macro and keep uncorrected solar time.
I agree with Willy Leenders that sundials should tell solar time. I have a
watch that can tell me mean time, but it has ceded to my celphone which is
even better.
Thanks for the question and thanks for the good answers. I keep learning
things here, many of which I should already know but somehow missed.
Jack
From: [email protected] [mailto:[email protected]] On
Behalf Of John Carmichael
Sent: Wednesday, February 09, 2011 6:46 PM
To: 'Donald Christensen'; [email protected]
Subject: RE: part 2 of longitude correction
(I hit the wrong button in my last email and it went out without my letter-
sorry!)
Hi Donald:
I understand your question, because I had this same question years ago when
I was a beginner.
The answer is no.
To re-phrase your question so that everybody understands it, you are asking
this- When drawing a sundial face, should you simply rotate the normal solar
time hour lines about their center of origin by 3 degrees to obtain a
longitude corrected face?
No, you can not do this. Each hour line has to be calculated and drawn
individually. This is a common error some beginning dialists make when
designing longitude corrected dials. I almost made this mistake too once!
To help you out (since a picture is worth a thousand words) I drew your
sundial in five minutes using Shadows Pro and sent it you off list the
drawing. I just didn't want you to make a common mistake. But verify it
for yourself and don't take my word for it. That's how you learn!
Keep asking good questions!
Thanks
John
From: [email protected] [mailto:[email protected]] On
Behalf Of Donald Christensen
Sent: Wednesday, February 09, 2011 3:52 PM
To: [email protected]
Subject: part 2 of longitude correction
I'm laying out lines for a new dial
I may not have been clear. I don't intend to rotate the gnomen. The dial
will still point true north
By labeling 12:12 as noon and 13:12 as 13:00, I am rotating the hour marks.
My question is,
Is it by an even 3 deg?
--
Cheers
Donald
0423 102 090
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So there!
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