Article of the month April

Spherical Gnomon

Place a sphere on a horizontal plane and use it as the gnomon for a sundial.
Here is an idea of what it would look like.

The sundial reads apparent solar time.
The hour lines lie in the same direction as on a normal horizontal sundial, but they are displaced, and do not meet in one point.

The shadow of the sphere on the dial face has the shape of an ellipse.
The time is read at the hour line tangent to the shadow ellipse.
In the drawing, it is three hours after noon.

In the morning hours, read the dial at the left side of the shadow ellipse. In the afternoon hours, read at the other side.

The idea is not new. Below is a photograph of a small model that was made years ago.

Model by Adolf Peitz, Germany.