heliostat |
A movable flat mirror used to reflect sunlight into a fixed solar telescope. Solar telescopes are large structures with long focal lengths but they need to point only at a small part of the sky. The heliostat is controlled so as to move synchronously with the motion of the Sun across the sky. It is a simple device but produces an image that slowly rotates during the course of a day, so the more complex coelostat is sometimes preferred. |