Coronagraph

A coronagraph is an astronomical telescope specially designed to study the corona of a star.

The principle of the coronagraph is to obscure the star using a mask (a metal disk or cone) of the same apparent diameter as the image of the luminous central part of the star (the photosphere) provided by the observing instrument.

It was devised by Lyot in 1930 to study the solar corona outside of eclipses. The coronagraph is still used to observe both the Sun's environment and those of other stars, and in particular to look for traces of any planetary systems.