Word Study
coelostat
CIDE DICTIONARY
coelostat, n.
an optical instrument used to follow the path of a celestial body and reflect its light into a telescope; it has a movable and a fixed mirror. [WordNet 1.5]
OXFORD DICTIONARY
coelostat, n. Astron. an instrument with a rotating mirror that continuously reflects the light from the same area of sky allowing the path of a celestial body to be monitored.
Etymology
L caelum sky + -STAT
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