The light color area which indicates more sunlight is called Yang (Sun). The dark color area has less sunlight (more moonlight) and is called Yin (Moon). Yang is like man and Yin is like woman. Yang wouldn't grow without Yin. Yin couldn't give birth without Yang. Yin is born (begins) at Summer Solstice and Yang is born (begins) at Winter Solstice. Therefore one little circle Yin is marked on the Summer Solstice position. Another little circle Yang is marked on the Winter Solstice position.
In general this symbol is a Chinese representation of the entire celestial phenomenon. It contains all, the cycle of the Sun, Moon, the four seasons.
Size: approx 3/4" width and height (excluding the fitting)