CORONAGRAPH

telescope that produces an artificial total eclipse of the Sun inside the instrument so that the Sun's corona and prominences may be observed. It was invented in 1930 by the French astronomer Bernard Lyot and first used by him at the Pic du Midi Observatory in the Pyrenees. A round metal screen blocks the overwhelming brightness of the Sun's central disk, or photosphere. Other screens and diaphragms block reflections of the photospheric image. The coronagraph must be used at high altitudes and on very clear days, when the atmospheric diffusion of light is at a minimum; imperfect lenses or dust inside the instrument will scatter enough photospheric light to obscure the dim corona.