heliostat

noun1

1. •
   A device that includes a plane mirror which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space, and is almost always stationary relative to the heliostat, so the light is reflected in a fixed direction.

   • Each heliostat can be directed to bathe a particular park bench or tree in a beam of light. […] The three heliostats cost $355,000 together, not apiece. — 2005