A Heliostat is a device that tracks the movement of the sun. Its most common use is to direct a mirror which reflects sunlight onto a fixed spot. It was a key instrument used in surveying, allowing the accurate observation of a known point from a distance.
It is also used in Solar Energy collectors as well as Solar observatories.
The simplest devices would use a clockwork mechanism to turn the mirror in synchronisation with the roatation of the Earth. More complex devices need to compensate for the changing elevation of the Sun throughout a Solar year.