The second physical process to consider is the transport of energy from the interior of the star to the edge. This situation is analogous to a pot of water on a stove, in which heat is deposited at the bottom by the stove burner, and is transported upward through the water to the surface where it can escape. In the case of a star, the temperature of the gas determines the density structure via the hydrostatic equilibrium condition, so understanding the transport is important. Radiation is the mechanism by which the Earth receives heat from the Sun, and its efficiency depends on the opacity of the material that the radiation must traverse. Opacity is a measure of the transparency of a gas, and it depends on the gas temperature, density, and elemental composition in a complicated way.
Convection is analogous to the turbulent motion in a pot of water as it boils.
In addition, convection can only operate if it transports more heat than radiation. The details of the efficiency of convection are not well understood, and they are probably the major source of uncertainty in the study of stellar structure and evolution. A third energy transport mechanism, conduction, is relatively unimportant in stellar interiors. Convection is likely to be important in determining other properties of the star. The existence of a hot corona may be associated with active convection in the outer layers, and the depth of the convective layer determines the extent to which material from the deep interior of the star is mixed into the outer layers.