The device that tracks the movement of the sun is called a sundial.

Here's how it works:

* The Gnomon: A sundial has a vertical stick or pointer called a gnomon.

* Shadow: As the sun moves across the sky, the gnomon casts a shadow.

* Marked Surface: The shadow falls on a marked surface, usually a flat plate or curved dial. The markings on the surface indicate the time of day based on the shadow's position.

While sundials are an ancient technology, they are still a fascinating way to tell time and understand the sun's movement.