Gas in the corona is extremely hot at 1 million degrees K. Temperature in the Corona rises with altitude. The extreme high temperature of the Chromosphere and Corona is not well understood by laws of physics. It is one of the mysteries to be revealed in the nature. The outer Corona is so hot, that the sun cannot hold it in place. Rotation of the sun moves the sunspots.
Sunspots consists of dark center umbra and outer border penumbra.
Its size is 40 sec of arc, about twice the diameter of the earth. Usually appear in pairs or groups. Large group may have 100 sunspots lasting about two months when in its peak level of activity. Actual color would e brilliantly orange at temperature of 4240 K. Large difference in brightness is due to fourth power dependence on temperature. Zeeman in the solar spectrum provides quite a bit of information about the sunspot.