Hi to all,
In the attached gif-file one can see the hour lines (apparent time):
red lines: hour lines without longitude correction
gray lines: hour lines with longitude correction for 5 degrees (= 20 minutes
of time)
North is vertical up (= 12 local apparent time ... green).
One cannot say that all hour lines are rotated by equal angles of 5 degrees.
Helmut Sonderegger
----- Original Message -----
From: Tony Moss
To: sundial@uni-koeln.de
Sent: Thursday, February 10, 2011 11:35 AM
Subject: Re: longitude correction
On 09/02/2011 21:49, Donald Christensen wrote:
How do I design a longitude correction in my sundial?
Correct me if I'm wrong
My horizontal dial is for Brisbane. The longitude is 153 deg and the
standard meridian is 150. This is a 3 deg difference.
I'll then rotate the hour lines by 3 deg to compensate
--
Cheers
Donald
0423 102 090
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So there!
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Hi Donald,
With any horizontal dial, if you are a whole number of
degrees to the East or West of your reference meridian, the gnomon remains
pointing true north and the hour/minute line divisions are unchanged: you
simply move the *numerals* around by the amount of the longitudinal correction
and choose the corresponding divisions to be your hours, halves and quarters.
Myself I prefer the symmetry of an uncorrected layout with the longitudinal
correction incorporated in the Equation of Time table or graph. In the latter
case you simply move the graph plot up or down from the zero line by the amount
of the LC. This is also easier when the LC isn't a whole number of degrees.
I'll leave you to work it out which way you have to move the numerals in this
case.
Hope this simplifies it.
Tony Moss
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