Coronal hole
Videos
A coronal hole is a region of the Sun's corona that appears dark in extreme-ultraviolet and soft-X-ray images because its plasma is cooler and more rarefied than the surrounding corona. Despite its na
When observed in extreme ultraviolet, coronal holes appear as relatively dark patches in the Sun's corona. Here, there is a big coronal hole in the northern hemisphere.
When the Sun's disk is obscured during a total solar eclipse or by a coronagraph (pictured), coronal structures not otherwise visible can be observed above the limb.
Space weather effects
Helmet streamer
Videos
Helmet streamers, also known as coronal streamers, are elongated cusp-like structures in the Sun's corona which are often visible in white-light coronagraphs and during solar eclipses. They are closed
Solar minimum
Solar maximum
Solar eclipse, Miles Landing 8 21 17