Article of the month November

Equator projection sundials 4

Another projection, which also produces a circular hour scale, is the central projection.
Here, projection is not from infinity as in the previous months, but from a point on the circle of the celestial sphere.
Although the resulting hour scale is circular, the hour points are no longer equidistant.

The gnomon should intersect the projection point.
The angle that the gnomon makes with the horizontal plane is variable.

The next drawing is an impression of such a sundial.
The bottom of the gnomon is set to the current date with the help of a small ring magnet.
In this example, the gnomon is a weighted string, but an elastic cord would work as well.

Here, a pole style is used for the support of the projection point, and an ordinary pole style hour-line pattern is added to the sundial.
This combination is self-aligning. This means that the sundial is oriented correctly when both systems indicate the same time.