Year 2005

Work of our members

Sundial reads like a clock

A well-known equatorial sundial with minute hand is shown below.
A rotating sight in the equatorial plane is set to the date and aimed at the sun.
One may then read the time on the equatorial plane.

The rotation of the sight, through a gear ring, makes a minute pointer move. Fifteen degrees of sight rotation equal one hour, and cause the minute hand to move through a complete circle once. This system allows one to read time to the minute.

The equatorial sundial shown below is based on this idea. Its equator plane is divided not in 24, but in 12 hours.
Moving the sight by 15 degrees makes, through a reducing gear, an hour hand move through 30.
Because of this, the dial gets the aspect of an ordinary clock.
There is no minute hand, but there is no reason why one could not be added.

A slip link allows one to move the hand with respect to the sight, adjusting for longitude and/or equation of time.

This page shows photographs of the sundial. The equatorial disk has a diameter of 34 cm or 13 ½ inches.

A view of the mechanism