siderostat

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siderostat

(sid -ĕ-rŏ-stat) A flat mirror that is driven in such a way as to reflect light or infrared radiation from a celestial body to a fixed point, such as a spectrograph slit at the coudé focus of a telescope, over the duration of an observation. A siderostat is often installed outside the main dome of an observatory and can be used with a coudé spectrograph, say, at the same time as the main telescope is being used to study a different field of view. Siderostats often have computer-driven altazimuth mountings.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Siderostat

 

an auxiliary astronomical instrument whose principal component is a plane mirror. The mirror moves in such a way that it reflects the light rays from a heavenly body in a fixed direction, in spite of the apparent diurnal rotation of the celestial sphere. A siderostat is used to direct the rays of a heavenly body into a fixed telescope. The mirror of the siderostat rotates around two mutually perpendicular axes. A siderostat used to observe the sun is called a heliostat. A primitive form of siderostat was used as early as the 17th century. In the 18th century the use of a clockwork mechanism was introduced for the rotation of the mirror.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

siderostat

[′sid·ə·rə‚stat]
(optics)
A more precise model of a heliostat; the siderostat uses a modified mirror mounting so that the image of a star is kept steady while the rest of the field is in rotation about the center.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.