Sundials, Altitude Altitude sundial, English, c 1570

Sundials, Altitude Altitude sundial, English, c 1570. Most sundials work by charting the sunÕs movement using the shadows cast by a fixed style or gnomon, but an altitude dial depends on the SunÕs altitude (or height above the horizon) to tell the time. The dial is calibrated with date marks as well as time marks, and the user must know these before pointing the gnomon directly at the sun and measuring the angle of the height of the sun from the shadow of the arc on the scale. This example was made in silver by Humphrey Cole (d 1591). ©SSPL/Science Museum