Corona

Corona is a layer of plasma (over heated gas) surrounding  the sun . Corona cannot be seen by the naked eye unless there is a total solar eclipse because the corona's glow is a million times lesser than the photosphere's but it can also be observed through a coronagraph or a coronameter which can block the light of the sun using an artificial disk so that the items surrounding the sun can be observed . Three types of corona have been observed using the coronagraph , they are :
1) The White Light Corona
2) The Emission Line Corona
3 The X-ray Corona