Questions about telescope attachments designed to block the direct light from a star.
A coronograph is a device used in combination with a telescope, to block out direct light from a star. This makes it possible to see objects along a nearby line of sight, that would otherwise be hidden by the glare of the star.
The first coronograph was installed on a telescope at the Pic du Midi in France by its inventor, Bernard Lyot, in 1931. Coronographs were first invented to observe the corona (hence the name) of the Sun. Nowdays, they are also used to detect exoplanets.
Today, many space observatories, such as the HST and SOHO feature coronographs. These are much more efficient in outer-space than if the same instruments were installed on Earth, since atmospheric scattering causes glare in the images.