The Caltech Alumni Association Analemmatic Sundial

The sundial is a gift of public art to the California Institute of Technology on behalf of the Caltech Alumni Association.

What is an analemmatic sundial?

An analemmatic sundial is a horizontal ellipse with a vertical gnomon (the part of the sundial that casts the shadow – in this case, you). The gnomon (again, you) moves depending on the time of the year to account for the declination of the sun. This is unlike the more common sundial you may be used to seeing that uses a fixed, triangular gnomon.

This is but a very, very simple explanation. For more information on analemmatic sundials, click here. Interested in learning about the different types of sundials? Click here.

How do you use it?

The roman numerals on the plinth indicate the first day of each month. Stand on the plinth at today's date, and your shadow marks the time.

To be more precise: the sundial is at 34º 08' 13" N and 118º 07' 25" W. Pacific Time is centered at 120º W, so there is a 7.5 minute time difference. The elliptical orbit of the earth requires an additional Equation of Time correction as a function of the date. For more information, click here (pdf).

Where is the sundial?

It's on the Caltech campus, south of the Winnett Center (map).

How was it constructed?

Funny you should ask. Learn all about the construction and see photos of the progress here.

 

 

Caltech Alumni Association 345 S. Hill Ave. Pasadena CA 91125 (626) 395-6592