- Corona is the outermost layer of the Sun. - It experiences a very high temperature, about one million degrees Celcius. - It starts at about 2100 km above the photosphere. - Corona isn't visible from the earth (except during solar eclipse). - The corona does not have an upper limit. - Photosphere, the Chromosphere, the Transition Region, and the Corona are the outer layers of the sun. - Granules on the sun's photosphere are due to the convection currents of plasma within the Sun's convective zone.