Answer:
When the Earth rotates on its axis, the Sun moves across the sky, causing objects to cast shadows. So, how does a sundial work? As the Sun changes relative positions in the sky over the day, the position of the shadow cast by the gnomon changes to align with the different times around the outside of the circular plate. This way you can tell the time by looking at where the shadow is cast, using the markings around the edge of the sundial base.
