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(kərō`nəgrăf'), device invented by the French astronomer B. Lyot (1931) for the purpose of observing the coronacorona,
luminous envelope surrounding the sun, outside the chromosphere. Its density is less than one billionth that of the earth's atmosphere. The corona is visible only at the time of totality during a total eclipse of the sun.
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 of the sun and solar prominences occurring in the chromospherechromosphere
[Gr.,=color sphere], layer of rarefied, transparent gases in the solar atmosphere; it measures 6,000 mi (9,700 km) in thickness and lies between the photosphere (the sun's visible surface) and the corona (its outer atmosphere).
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. Because of the intense light of the sun, the corona and chromosphere can ordinarily be seen only during a total eclipseeclipse
[Gr.,=failing], in astronomy, partial or total obscuring of one celestial body by the shadow of another. Best known are the lunar eclipses, which occur when the earth blocks the sun's light from the moon, and solar eclipses, occurring when the moon blocks the sun's light
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. The coronagraph consists of two refracting telescopes in tandem. A solid disk placed in front of the prime focus of the first telescope plays the part of the moon and eclipses the sun's image in the telescope so that only the outer layers of the sun's atmosphere are focused by the second telescope onto photographic film. A monochromatic filter is also used to improve optical clarity and remove chromatic aberration.


(kŏ-roh -nă-graf, -grahf) An optical instrument designed in 1930 by the French astronomer Bernard Lyot for observing the solar corona at times other than a total solar eclipse. In the coronagraph, the bright image of the Sun is artificially eclipsed by means of a blackened occulting disk set at the prime focus of the objective lens of a refracting telescope. A lens is used because the scattering of light from its surface is much less than is the case with a mirror. It is important to reduce scattering to a minimum if the faint light of the corona is to be recorded on the photographic plate or other detector. To reduce atmospheric scattering, high-altitude sites are used; coronagraphs have also been operated from satellites, rockets, and balloon platforms. A narrow-band interference filter is usually placed in front of the detector so that the emission lines of the E-corona can be studied.



a telescope used for observation of the corona of the sun. Since the light scattered from the sun’s photosphere in the earth’s atmosphere and in the telescope is hundreds of times brighter than the light of the sun’s corona, the latter was observed until the 1930’s only during total solar eclipses, when the photosphere is covered by the moon. The coronagraph used for such observations is a long-focus photo-graphic camera, usually mounted horizontally; the light to it is supplied by a coelostat. The standard coronagraph used in the USSR has an objective of 5-cm diameter and 500-cm focal length.

Observations of the corona of the uneclipsed sun became possible after the invention of a coronagraph by the French astronomer B. Lyot, by means of which he first observed the corona at the observatory at Pic-du-Midi (France) in 1931. The corona-graph used to observe the uneclipsed sun consists of a primary objective that forms an image of the sun on a metallic disk, which occults the light of the photosphere and thus produces an artificial eclipse. In order to eliminate the scattered light that appears around the edge of the primary objective as a result of diffraction, a lens is placed behind the metallic screen. This lens forms the image of the primary objective on a diaphragm, which has an opening too small to pass the image of the edges of the primary objective. A second objective forms the final image of the corona or prominences on a spectrograph slit or on a photographic plate. In the last case, the light passes through a monochromatic interference-polarization filter, which removes all rays except the spectral line of the corona or prominence being studied. The use during observations of special filters with a density that decreases from the center to the edges makes it possible to obtain images of the bright inner part and of the fainter outer part of the corona on the same photograph.

Coronagraphs provide best results when set up on mountains, where the atmospherically scattered light is significantly less. In the USSR the first observations of the corona of the uneclipsed sun were made at the Kislovodsk Mountain Astronomical Station in 1950, using a coronagraph with an objective of 20-cm diameter. The largest coronagraphs in the world, with objectives of 53-cm diameter, are located at this station and at the observatories near Irkutsk, in Abastumani, and in Alma-Ata.


Gnevyshev, M. N. Kislovodskaia gornaia astronomicheskaia stantsiia. Moscow-Leningrad, 1965.
Martynov, D. la. Kurs prakticheskoi astrofiziki, 2nd ed. Moscow, 1967.



An instrument for photographing the corona and prominences of the sun at times other than at solar eclipse.
References in periodicals archive ?
As a demonstration of this technique an exoplanet that was previously hidden in the glare of the light of the host star spilling past the coronagraph, was recently revealed in an 1998 Near Infrared Camera and Multi-Object Spectrometer (NICMOS) image.
Dorst gave the obligatory warning of the danger inherent in this challenging observation; 'observers should not risk their eyesight by pointing a telescope toward the Sun without adequate safety precautions and should recall that no telescope can be made to show the corona or prominences without a proper coronagraph or narrow-band filter.
The continuous operation of the LASCO coronagraph since 1996 has resulted in the longest and most complete database of CME properties ever assembled.
Large plates of the Sun were taken twice daily with the Photoheliograph and a continuous record of Solar surface activity was made on 35mm film with the Lyot Coronagraph.
A random graze of topics turns up scientific output of single-aperture imaging of exoplanets, tidal constraints on planetary habitability, resolved imaging of extra-solar photosynthesis patches with a laser-driven hypertelescope flotilla, how to consolidate efforts within the community and the related agencies, the extraterrestrial life debate in different cultures, and the ExtraSolar Planetary Imaging Coronagraph.
Search for brightness variations in FeXIV coronagraph observations of the quiescent solar corona.
3 in LASCO C2 coronagraph images, moving southward from directly underneath the occulter; the comet brightened and showed a nice tail before entering the C3 field of view, where it began to fade [IAUC 7694, 2001 Aug 28].
Exo-C's coronagraph is similar to what some ground-based planet-hunting telescopes use already.
Hours before ISON reached perihelion, stunning images taken by SOHO's Large Angle and Spectrometric Coronagraph (LASCO) showed the bright, elongated tail of the onrushing comet.
A coronagraph blocks out the glare of the central star so that the disk can be seen.
Tenders are invited for: Prototype compact wide angle coronagraph
Another group, led by Karl Stapelfeldt of NASA's Goddard Space Flight Center, is studying the alternative method known as a coronagraph, in which the occulting disk is inside the telescope.