This page introduces a unique instrument which uses a laser beam to simulate rays of sunlight. The purpose of the instrument is to lay out large and complicated sundials.

The device was made out of a small transit. A transit has two axes of rotation which are aligned at right angles to each other. The Laser Trigon uses these two axes to control the direction of a laser beam so it can project sundial hour lines, as well as the lines and curves of the sun's declination, onto any surface, regardless of orientation or complexity.

Once in position, the Laser Trigon becomes a model of the celestial sphere as it relates to the position of the sun and the local site. The instrument is mounted so the 96 tooth index gear lies in the plane of the equator where it becomes an auxiliary equatorial dial. The 96 teeth provide the hour angles for 24 hours sub-divided into quarters. The laser is moved along the hour lines by sweeping the declination motion

The declination index (the vertical motion of the original transit) is at right angles to the equatorial index, thus in position to control the laser for the lines and curves of declination. This index has three positions corresponding to the solstices and the equinoxes. When used to locate a declination, the equatorial motion is free to sweep from side to side.

Below are three sketches of the Laser Trigon in position to draw declinations on a dial at latitude 40°. From left to right the declination index is shown in position to project the equinoxes, the winter solstice, and the summer solstice.

A more complete discussion of the Laser Trigon, including a description of its origins in traditional dialing tools can be found in Compendium 3-2 of the North American Sundial Society (June 1996).

I recently built a large experimental sundial by using the Laser Trigon to project a dial on a very unusual object.