optical device used to follow the path of a celestial body and reflect its light into a telescope; has a movable and a fixed mirror
例句
As a coelostat, MA tracks the motion of celestial objects observed at their meridian passages. MA作为定天镜跟踪天体的运动，望远镜在天体中天前后进行观测。
The aperture of the coelostat mirror is 460 mm. The objective mirror, 330 mm in diameter, has primary focal length of 21 m and Cassegrain focal length of 40 m, corresponding solar image with diameter 200 mm and 373 mm respectively. 塔高约21m,定天镜口径460mm,成象镜口径330mm,主焦距21m,卡式焦距40m,相应的太阳像直径分别为200mm和373mm。
