The Collaborative International Dictionary
Siderostat
Siderostat \Sid"er*o*stat\, n. [L. sidus, sideris, a star + Gr. ??? standing, fixed, fr. ???? 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.
Wiktionary
siderostat
n. (context astronomy English) A heliostat that may be used with stars as well as the sun