siderostat

n. [ L. sidus, sideris, a star + Gr. &unr_;&unr_;&unr_; standing, fixed, fr. &unr_;&unr_;&unr_;&unr_; to place. ] (Astron.) An apparatus consisting essentially of a mirror moved by clockwork so as to throw the rays of the sun or a star in a fixed direction; -- a more general term for heliostat. [ 1913 Webster ]