an astronomical instrument consisting of a plane mirror mounted parallel to the earth's axis and rotated about this axis once every two days so that light from a celestial body, esp the sun, is reflected onto a second mirror, which reflects the beam into a telescope
Compare siderostat
Word origin
C19 coelo-, from Latin caelum heaven, sky + -stat
coelostat in American English
(ˈsiləˌstæt)
noun
an optical system, used with a fixed telescope, consisting of two mirrors with a moving mirror mounted on an axis parallelto the earth's axis of rotation and driven by clockwork so as to reflect the same portion of the sky continuously or to track the sun