Philip P. Pappas, II wrote:
> Hello dialists:
>
> Hoping that I might get your help with one last question that needs
> answering before the new edition of my Sundial Owner's Manual goes to print.
> In the chapter on setting a (horizontal) sundial, I recomend that a dial
> should be oriented north not by a compass and not by polaris but by the
> "time method". I say that this method is the most accurate but will only
> work on those dials that are properly designed, constructed and leveled.
> Correcting for the Equation of Time and longitude, using a reliable time
> source, the sundial should automatically point north if it reads the right
> time.
Let me hitchhike on your question after turning it upside down: if we orienta
sundial using the method described above, how precise can we expect
the orientation to be? In my case we would be trying to find the South, of
course.
I must presume it also depends on the size of the dial, the thickness of the
hour lines, the hour of the day, the precision of the gnomon, if it has
or does not have longitude correction, etc.
If we could take all those factors into account, can we expect to have a
better reading than one provided by a compass?
- fernando
PS - By the way, I would ask you guys that write about sundialling to always
take into account the fact that we live in a global village. People like
myself buy sundials in the northern hemisphere in the hope to be
able to use in the sourthern hemisphere. If the books and leaflets
are always referring to the Polaris, to the North, so on and so forth,
common people will never be able to correctly orient a sundial.
>
>
> Then I say that you can set a horizontal dial with greater precision in the
> early morning or late afternoon because the space between the minute lines
> is larger at those times
> (This is when the shadow points due east or due west). It is easier to
> read a dial at those times because the lines aren't as bunched up as they
> are at apparent noon.
>
> Here's my question: Is a sundial more accurate when the sun is setting or
> rising? Is the benefit of larger spacings between the minute hands wiped
> out by atmospheric effects (refraction and the mirage effect.)? By the way,
> does anybody know by how many minutes an actual sunset precedes the apparent
> sunset?Does this amount vary with latitude and seasons?
>
> Sorry, one question turned into four!
>
> Thanks for your help
>
> John Carmichael
--
Fernando Cabral Padrao iX Sistemas Abertos
mailto:[EMAIL PROTECTED] http://www.pix.com.br
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19º 37' 57.0" S 45º 17' 13.6" W
