Heliostat                                or,return to Home Page

 1/ –noun
an instrument consisting of a mirror moved by clockwork, for reflecting the sun's rays in a fixed direction.

[Origin: 1740–50; < NL heliostata.


2/ An instrument in which a mirror is automatically moved so that it reflects sunlight in a constant direction. It is used with a pyrheliometer to make continuous measurements of solar radiation.


 Just an idea... In underdevelopped (sic) countries sophisticated devices don't usually last long, and an external, usually electrical, power source can be hard to come by.


The long matt-black cylinders contain a volatile liquid, probably Ethylene Chloride. They are separated by a reflective metal blade, aligned on the desired axis.

As the Sun turns in the sky, one of the cylinders will fall into shade, and cool. The falling pressure allows the connected capsule, as in an anaeroid barometer, to contract. The hotter capsule will follow this movement, and through a central wheel, moves a pivoted arm the end of which carries at its extremity a pawl. In moving forwards this pawl bears on a fixed quadrant, and thus entrains the entire mechanism, including the solar collector, with it.