Such instruments are commonly known as coronagraphs or coronameters , depending on design.
Streamers are again clearly visible.
This is a first indication that the global, large-scale structure of the corona evolves in a manner that is at least partially decoupled from the evolution of active regions. Note how coronal holes can also be seen in white light, as regions devoid of helmet streamers or other bright coronal structures. The fact that coronal holes look dark in white light indicates lower gas densities than in bright structures such as helmet streamers. Coronal holes look dark in X-rays in part because of the lesser densities, but also because less heating occurs there. This suggest that coronal holes are regions of open magnetic fieldlines, along which coronal gas can flow outward into interplanetary space in the form of the solar wind.