An Etymological Dictionary of Astronomy and Astrophysics
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An optical instrument for viewing an overlapping pair of photographs (or perspective drawings) in order to see a three-dimensional image.

→ stereo-; → -scope.

An instrument used to collect and amplify light or other energy. → Refracting telescopes gather light by means of a lens, → reflecting telescopes by means of a mirror. → Radiotelescopes gather radio energy by using an antenna. Telescopes have also been built that can gather X rays, gamma rays, and other forms of energy. → grazing incidence telescope.

From It. telescopio (used by Galileo, 1611), and Mod.L. telescopium (used by Kepler, 1613), both from Gk. teleskopos "far-seeing," from → tele- "far" + -skopos "seeing," from skopein "to watch, look, behold;" → -scope.

Durbin, from dur-, → tele-, + -bin "to see; seer," → -scope.

A covering, usually hemispherical, that is rotatable about a central axis. There is a slit opening along one side wide enough to allow a telescope to be directed at any vertical angle up to 90°.

→ telescope; → dome.

The accuracy with which a telescope can be pointed to a particular coordinate in the sky.

→ telescope; → pointing; accuracy.

A telescope, usually of long → focal length, that is situated underneath a tower. Tower telescopes are mainly used for observation of the Sun. See also → solar telescope; → solar tower.

→ tower; → telescope.

Same as → transit instrument.

→ transit; → telescope.

A Belgian facility devoted to the detection and characterization of → exoplanets and to the study of → comets (→ transiting planet) and other → small solar system bodies. It consists of two 60 cm robotic telescopes located at the → European Southern Observatory, → La Silla, in Chile and at Oukaïmden Observatory in Marroco.

→ transit; → planet; → planetesimal; → small; → telescope.

An observing facility consisting of four 8.2 m telescopes, with the combined collecting area of a 16 m mirror, owned and operated by the European Southern Observatory at an altitude of 2635 m at the Paranal Observatory in Chile. The four reflecting unit telescopes are called Antu "Sun" in the language of Chile's indigenous Mapuche people, Kueyen "Moon," Melipal "Southern Cross," and Yepun "Venus." Each unit is equipped with several sophisticated instruments. The light of the individual telescopes can be combined using interferometric techniques to achieve superior resolution. → VLT Interferometer (VLTI). The wavelength range covered by the VLT is extremely wide, ranging from deep ultraviolet to mid-infrared.

→ very; → large; → telescope.

A → grazing incidence telescope designed to observe → X-ray emission from astronomical objects. Wolter telescopes use a combination of two elements, a parabolic mirror followed by a hyperbolic mirror and come in three different optical configurations. The design most commonly used by X-ray astronomers is the Type I since it has the simplest mechanical configuration. In addition, the Type I design offers the possibility of nesting several telescopes inside one another, thereby increasing the useful reflecting area. This is an extremely important attribute, since virtually all X-ray sources are weak, and maximizing the light-gathering power of a mirror system is critical. The → Chandra X-Ray Observatory is a Wolter Type I telescope that has four thick nested mirrors coated in iridium. The Japanese X-ray observatory Suzuki uses a conical approximation of the Wolter Type I design. Its mirrors are coated in gold, and they are far thinner than the ones used in Chandra. This allows for denser nesting, so there are 700 mirrors instead of four. The result is a much higher collecting efficiency at a reduced weight. For comparable apertures and grazing angles, the primary advantage of Type II over Type I is that higher magnifications are attainable. This is because the second reflection is off the outside of a surface, which allows longer focal lengths. However, since off-axis images suffer much more severely from blurring in Type II configurations, the Wolter Type II is useful only as a narrow-field imager or as the optic for a dispersive spectrometer. The Wolter Type III has never been employed for X-ray astronomy (NASA Imagine the Universe!).

Named after Hans Wolter (1911-1978), a German physicist who designed the optical configuration.

A telescope designed to focus X-rays from astronomical objects. X-ray telescopes function from orbital satellites because X-rays are absorbed by the Earth's atmosphere. These telescopes require special techniques since the conventional methods used in optical and radio telescopes are not adequate. → grazing-incidence telescope; → Bragg angle.

→ X-ray; → telescope.

A → telescope that is mounted on a → vertical axis or moves only a small amount from the vertical. It is primarily used to determine positional measurement of stars moving near the → zenith. The advantage is that there is no → atmospheric refraction occurring at the zenith. If a star on one night passes through the center of eyepiece, one must observe it six month later, and see if the star has been offset by the center. A shift would mean a measure of parallax. See also: → zenithal well.

→ zenith; → telescope