A coronagraph is a device attached to a telescope. This device is designed to block out the light made by star in order to see its corona as well as other stellar bodies that cannot be seen due to the light of the star. The coronagraph basically operates in the same principle as an eclipse.
During an eclipse the moon blocks the light of the sun allowing us only to see its corona. Also, in an eclipse we get to see stars that are usually blocked by the light of the sun. The coronagraph creates an eclipse within the telescope allowing the observer to see stars and other stellar bodies. The coronagraph was initially designed to observe the sun’s corona. However later developments to the device and deeper understanding of physics and astronomy expended the use of these devise to look for extra-solar planets among other things.
While initially the coronagraph was designed to observe our own sun, modern day coronagraphs are adapted for use on farther stars allowing scientists to see other stellar bodies or phenomenon that are covered by the star’s light. This device has allowed us to discover more about our universe. There are even satellite based telescopes equipped with coronagraphs.