Whats the difference between a “CME” and a “Halo CME” ?
The difference is primarily a matter of perspective. Coronal mass ejection (CME) is the name given to an ejection of a large amount of matter from the Sun’s outer atmosphere. These ejections typically comprise millions of tons of material in the form of charged particles, and can be seen because the material reflects sunlight. When one of these ejections is directed towards the Earth (or conversely, directly away from the Earth), it looks like a roughly circular “halo” surrounding the Sun. The “halo CMEs” then are those CMEs which are more likely to impact the Earth than those which are shot out at right angles to the Earth-Sun line.
