Gnomon Sundial

Yuan Dynasty (replica), Ancient Observatory, Beijing

The sundial's scale marks off the divisions between the summer and winter solstices (previous page) and, on the circle at the bottom, the 24 solar terms that partition the calendar into 24 equal parts based upon the movement of the sun around the equinoxes. The original gnomon (previous page) cast its shadow onto the long scale, plus a small spot of light through a pinhole and onto the solar circle.