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

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.

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 It might be outdated or ideologically biased.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.

Mentioned in

References in periodicals archive

Casting the massive, 2-meter siderostat mirror proved difficult.

The siderostat stood 10 meters tall at the north end of the Foucault Gallery in the Paul Gautier Room, under sections of roof and walls that could be slid to the north and south to expose the sky.

Deloncle himself tested the telescope on the first clear night when the Moon was observable with the siderostat. He wrote, "On the square ground-glass plate before our eyes [in the plateholder] the moon's image gradually crept up from one corner until it had overspread the glass completely.

Opening the roof took six to eight people, he reported, but only two were needed for observations: one adjusting the siderostat and the other adjusting the optics at the eyepiece end.

The siderostat mirror went to Paris Observatory, where it has long been displayed in the history building.

A siderostat mirror followed the turning sky and directed light into a 491/4-inch f/48 refractor, fixed horizontally.

Caption: BRINGING DOWN THE HEAVENS The 2-meter, flat siderostat mirror rode in an exquisitely smooth equatorial mounting, which could keep an object centered in the eyepiece more than 200 feet away for up for 45 minutes.

The lesson of the great Paris Telescope