convection: Convection is the process by which a liquid or a gas rises and falls because of a change in density brought on by heating and cooling. Heat moves from one place to another by the motion of a liquid or a gas. In one example, a pot of boiling water is very hot on the bottom and cooler at the water's surface. As the water bubbles and simmers, you can see it moving around. The water in the bottom of the pot is flowing to the top, and the water at the top flows to the bottom. This motion, caused by the circulating heat, is called convection. A similar phenomenon occurs in the interior of the Sun. Continuous currents of hot gas rise from the interior of the Sun, cool near the surface, and sink again.
