On July 5, 2011, the unnamed comet appeared to interact with plasma and magnetic fields in its surroundings as it fell apart. Could a puny comet cause a magnetic instability that might propagate and blossom into a impressive CME? The question is not so crazy as it once seemed to be.
A coronagraph is a telescope that can see things very close to the Sun. It uses a disk to block the Sun's bright surface, revealing the faint solar corona, stars, etc.