MY DESCRIPTION of the SUNDIAL at SIGNAL HILL

A SUNDIAL has two main parts. One is called the base and the other the gnomon. The gnomon, which is a small pointer, is centered and sits perpendicular on the base, casting a shadow from sunlight.

SUNDIALS VARY in design: some have a vertical base, some bases are horizontal and some slant. The base at Signal Hill slants.

ALL SUNDIALS incorporate the latitude of the site in either their gnomon, or in their base. The sundial at Signal Hill is known as a polar sundial, which means that its base slants toward the north pole. If a gnomon is placed upright on this base it will point toward the celestial equator, which is 90 degrees from the pole.

IN ORDER for the sundial base to point to the pole, it must point north and the slant of the base from horizontal must be equal to the latitude of the site, in this case about 32 degrees. The sundial rock at Signal Hill appears to have been supported from behind and underneath so that it has remained firmly in position, pointing north with a 32 degree slant, for perhaps 1000 years.

Sundial Diagram

NATIVE AMERICANS did not think in terms of measured degrees as we do, but the correct angle of the rock at Signal Hill could be determined over time by an observer watching the shadow of the gnomon as the base rock was slanted higher or lower.

THE SLANT ANGLE might have been determined earlier with a small model sundial. Accurate north-south orientation was determined by many ancient cultures using an upright stick in the ground and measuring its shadows.

A GNOMON can have various configurations. I found several small triangular shaped rocks on the ground near the slanted rock; each would serve as a gnomon.

THE SUNDIAL DRAWING at SIGNAL HILL, with a FOUND ROCK GNOMON, SHOWS the FOLLOWING:

1) NOON as well as approximate MORNING and AFTERNOON time. The morning shadow points west and the afternoon shadow points east.
2) Approximate DAY of the equinox. The shadow disappears at noon. The morning and afternoon shadows are horizontal.
3) SEASON of the year. The gnomon shadow points above the horizontal line in the fall and winter (after the autumnal equinox) and below the horizontal line during the spring and summer (after the vernal equinox).

My photographs illustrate these phenomena on the following pages.


next previous

Click on SIGNAL HILLcategory below if you would like to REVIEW or SKIP:

Introduction I Summer Solstice I Equinoxes I Winter Solstice I Lunar Calendar I Sundial I Counting Rock I Volcanic Eruption
Click HERE to return to Contents