Designing our Ariel Analemmatic Sundial

For our Ariel Astro Observatory, we are implementing an analemmatic sundial. It is optimized for a latitude of 33° 36' 48.9384'' N (Coto de Caza, California), and features a Star of David as a design element.

Analemmatic sundials are a type of horizontal sundial that has a vertical gnomon and hour markers positioned in an elliptical pattern. The gnomon is not fixed and must change position daily to accurately indicate time of day. Hence there are no hour lines on the dial and the time of day is read only on the ellipse As with most sundials, analemmatic sundials mark solar time rather than clock time. An analemmatic sundial is completely defined by:

1. The size of its ellipse (chosen by the designer).
2. The latitude of its location (determines the location of the hour markers on the ellipse).
3. The declination of the sun (determines the daily gnomon position).

Analemmatic sundials are sometimes designed with a human as the gnomon. In this case the size of the hour marker ellipse is constrained by human height and the latitude of the sundial location - since the human gnomon shadow must fall on the hour marker ellipse to accurately indicate the time of day. Human gnomon analemmatic sundials are not practical at lower latitudes where a human shadow is quite short during the summer months.