Television Telescope

an astronomical instrument in which images of celestial objects are formed by means of television technology. Television telescopes are used for observations in the ultraviolet, visible, and infrared regions of the spectrum. The first such instruments were used in 1952 for observations of the moon (Great Britain) and in 1954 for observations of Mars (USA). In the USSR the first observations of the moon with a television telescope were made in 1956 at the Pulkovo Observatory.

In a television telescope, an image of a celestial object or a portion of the sky is formed by an optical telescope and projected onto the photocathode of a television camera tube; storage tubes, such as image orthicons, vidicons, image isocons, and SEC camera tubes, are usually used for this purpose. The video signals produced by the tube pass through circuits for regulating the contrast and through video amplifiers and arrive at a kinescope. The image created on the kinescope screen can be photographed with a camera.

The television telescope has a number of advantages compared with an optical telescope. Specifically, the size, contrast, and brightness of the image produced are continuously variable, and the arrangement makes it possible to build up an image in the form of electrical charges accumulated on the target of the tube; the image may then be photographed. The electrical signals produced by a television telescope can be fed directly to a computer for automatic processing of the observation data; this eliminates laborious processes, such as chemical treatment of photographic films and film measurements. At the same time, the system has those disadvantages generally typical of television equipment: sensitivity is not uniform throughout the field, and distortions are present.

Television telescopes are used for photometric observations of stars. When used in conjunction with image-converter tubes, they make it possible to observe objects much fainter than those within reach of photographic techniques. They permit successful observations of low-contrast details in nebulae and on the surfaces of planets, especially cloud formations. They are also useful in studies of celestial bodies with rapidly varying magnitudes, such as observations of pulsars in the optical range, investigations of unstable stars, and searches for supernovae.

Television telescopes have also been used to observe poorly illuminated celestial objects, including artificial earth satellites and space probes. They are used for both astrophysical and astrometrical observations. In the latter case, the position of the celestial body under study is measured relative to reference stars that are visible on the kinescope screen and that have a position that is known from star catalogs.