The mottled appearance of the solar photosphere, caused by convective cells, resembling granules, which rises from the interior of the Sun. Each granule has a mean size of about 1,000 km and an upward
velocity of about 0.5 km/sec. Granules are separated by intergranular walls about 400 K colder. They emerge from the fragments of the preceding granules and their lifetimes are about 20 minutes.
The inner part of the solar corona which extends to about two solar radii. It is due to the Thomson scattering of light from the photosphere by the free electrons in the corona. The K corona exhibits
a linearly polarized continuous spectrum. The high speeds of the scattering electrons (on the average 10,000 km s^-1 for a temperature of 2 million K) smear out the Fraunhofer lines except the H and K lines.
The Sun's magnetic field which is probably created by the differential rotation of the Sun together with the movement of charged particles in the convective zone. Understanding how the solar magnetic
field comes about is the fundamental problem of Solar Physics. The solar magnetic field is responsible for all solar magnetic phenomena, such as sunspots, solar flares, coronal mass ejections, and the solar wind. The solar magnetic fields are observed from the Zeeman broadening of spectral lines, polarization effects on radio emission, and from the channeling of charged particles into visible coronal streamers. The strength of Sun's average magnetic field is 1 gauss (twice the average field on the surface of Earth, around 0.5 gauss), and can be as strong as 4,000 Gauss in the neighborhood of a large sunspot.