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coelostat

[see-luh-stat] /ˈsi ləˌstæt/
noun, Astronomy
1.
an apparatus consisting of a mirror driven by clockwork, used to enable a fixed telescope to keep the same area of sky in its field of view by compensating for the apparent rotation of the celestial sphere.
Compare siderostat.
Origin
1895-1900
1895-1900; coelo- (for Latin caeli-, combining form of caelum sky) + -stat
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for coelostat

coelostat

/ˈsiːləˌstæt/
noun
1.
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
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Encyclopedia Article for coelostat

device consisting of a flat mirror that is turned slowly by a motor to reflect the Sun continuously into a fixed telescope. The mirror is mounted to rotate about an axis through its front surface that points to a celestial pole and is driven at the rate of one revolution in 48 hours. The telescope image is then stationary and nonrotating. The coelostat is particularly useful in eclipse expeditions when elaborate equatorial mounting of telescopes is impossible. Other instruments applying the principle of the coelostat for similar observations are the heliostat, which produces a rotating image of the Sun, and the siderostat, which is like a heliostat but is used to observe stars

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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