1. An astronomical instrument consisting of a plane mirror rotated by a clockwork mechanism to reflect the light of a celestial body in a fixed direction, used in solar observation and spectroscopy.
Usage: technical; astronomy

Examples

• The observatory installed a coelostat to track the sun's position throughout the day.
• Astronomers use a coelostat to direct sunlight into a fixed spectrograph for analysis.
• The coelostat's rotating mirror compensates for Earth's rotation to keep the image stationary.
• Solar physicists rely on the coelostat to maintain a steady beam of light for long-term observations.