Hello John,
Thank you for another very interesting thread. This past Summer I
experimented with using a spherical gnomon whose shadow (oval in shape)
intersects concentric circles (one for every month) thereby allowing the
date to be indicated at local noon (i.e., the oval shadow intersects a
specific concentric circle uniquely for each day). This is one approach
to the problem of indicating date, which a vertical gnomon would have
difficulty doing, when the Sun approaches zenith.
As an FYI I've attached an image of the calculated shadow shape
at the three principal altitudes of the Sun (for my local), i.e., Summer
Solstice, Spring/Fall Equinoxes and Winter Solstice. Note that the shape
of the shadow starts off fairly circular (red object) when the Sun is
high in the sky (Summer Solstice) but becomes quite elliptical (blue
object) at the Sun's Winter Solstice altitude. The cross indicates the
center of the concentric circles, i.e., the origin. Just thought you'd
like to see it.
Best,
Luke
John Carmichael wrote:
>
> Hello all:
>
> I've been having lengthy discussions with Fer, Sarah Edmonson and Steve
...
> sundials and are designed on Zonwvlak using two different programs!!!
Attachment converted: Macintosh HD:oval.jpg (JPEG/JVWR) (0000F2ED)
