Coronagraph

Coronagraph, telescopic instrument, designed to observe the corona, the outer region of the Sun's atmosphere (see Sun). Before the invention of the coronagraph by the French astronomer Bernard Lyot in 1931, the corona could be observed or photographed only during total eclipses, since the luminosity of the corona is only one-millionth that of the Sun. Lyot employed an “occulting disc” to block out the Sun's image, in effect, producing an artificial eclipse. The coronagraph is usually mounted at a high altitude to avoid the scattering of light by particles and dust suspended in the atmosphere and includes a narrow-band polarizing filter to correct for chromatic aberration (see Optics).