John Carmichael wrote:
Hi Chris:
But I'm not so sure I agree with you about a flat disk with a small
hole. The aperture disk nodus you described works fine when the sun
is not at low angles relative to the face. example: a direct south
vertical wall dial around midday. But if it's early morning or late
afternoon, won't both the shadow of the disk and the projected solar
image elongate into long ellipses? In fact, if the sun is hitting the
disk nearly edge on, I bet the solar image projection might disappear
all together. If you could manually rotate the disk so that it is
perpendicular to the sun, then I would agree with you. But sundial
I'm designing is high above a doorway and can't be touched.
Interested in anybody's comments on this,
John
Quite the opposite, John!
If you did rotate the disk, so it was always perpendicular to the sun,
the shadow *would* elongate.
But, keeping the disk parallel to the shadow plane, it appears to
foreshorten, as the angle shrinks, resulting in the elongated shadow
foreshortening the same amount...
Dave
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