 Over the course of the year different sections of the rod serve as the style , which is the part of the gnomon that indicates the time by casting its shadow on the dial face . At the summer solstice , when the Sun is highest ( farthest above the equatorial plane ) , the style is closest to the top of the rod , and at the winter solstice , when the Sun is lowest , it is closest to the bottom . At the equinoxes , when the Sun is on the equatorial plane , the style is exactly in the center of the length of the rod . The style of the equatorial sundial is parallel to the Earth 's axis of rotation . 
