A) The corona is the outermost layer of the Sun's atmosphere.
The Sun is composed of several layers.
The sun's corona extends above the visible layers of the sun to about 1300 miles. It is only visible during an eclipse or through the use of a specialized telescope called a Coronagraph which creates an artificial eclipse by blocking out the bright surface of the sun itself.
The Photosphere, which extends from the Sun's surface to about 250 miles, is the layer upon which sunspots occur. Sunspots are caused by magnetic fluxuations that prevent the convection, or flow, of heat energy.
Most of the Sun's density is found in its inner Core.
